The material used most often in LEDs is gallium arsenide, though there are many variations on this basic compound, such as aluminum gallium arsenide or aluminum gallium indium phosphide.

What semiconductor material is used in the construction of LED Mcq?

LED MCQ – Objective Question Answer for LED Quiz – Download Now! An LED has lower output power, _ switching speed and _ spectral width than the LASER as an optical source.

1. slower, higher
2. faster, higher
3. faster, lower
4. slower, lower

Option 1 : slower, higher An LED is a junction diode made from semiconductor compound gallium arsenide phosphide. LEDs used as optical fiber transmitters emit infrared radiation at a wavelength of about 850 nm (0.85 µm). Laser is derived from Light Amplification by the Stimulated Emission of Radiation.

• • Collimated (meaning all parts travel in one and same direction)
• An LED has lower output power, slower switching speed and higher spectral width than the Laser as an optical source.

specification	Light Emitting Diode	Laser Diode
Working operation	It emits light by spontaneous emission.	It emits light by stimulated emission.
Output power	Emitted light power is relatively low, Linearly proportional to drive current	Output power is high (Few mW to GW), Proportional to current above the threshold
Spectral width	Wider, 25 to 100 nm (10 to 50 THz)	Narrower, -5 to 5 nm (
Speed	Slower	Faster
Coupled power	Moderate	High

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students The semiconductor material NOT used in LED is:

1. silicon carbide
2. GaAsP
3. GaAs
4. Si

1. Generally, optical devices are fabricated using direct bandgap semiconductors like GaAs and normal PN diode is fabricated by using Si,
2. The most basic material for the fabrication of an LED is GaAs (Gallium Arsenide).
3. Using GaAs as basic material, GaAs produces LEDs of different colors. This is as shown:

Semiconductor material	Wavelength	Colour
GaAs	850 – 940 nm	Infra-red
GaAsP	630 – 660 nm	Red
GaAsP	605 – 620 nm	Amber
GaAsP:N	585 – 595 nm	Yellow
AlGaP	550 – 570 nm	Green
SiC	430 – 505 nm	Blue
GaInN	450 nm	White

Si is not an LED material. India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students Study the given figures. Identify the elements from 1 to 4 and select the option that shows their correct names

1. 1: Zener diode, 2: Photo diode, 3: LED diode, 4: Junction diode
2. 1: LED diode, 2: Junction diode, 3: Zener diode, 4: Photo diode
3. 1: Photo diode, 2: LED diode, 3: Junction diode, 4: Zener diode
4. 1: Junction diode, 2: Zener diode, 3: Photo diode, 4: LED diode

Option 4 : 1: Junction diode, 2: Zener diode, 3: Photo diode, 4: LED diode PN Junction Diode :

• A unilateral device is a device that conducts only in one direction.
• p-n junction diodes conduct only when the p region is connected to higher voltage and the n region is connected to lower voltage.
• When reverse biased, it acts as an open circuit.
• The symbol for a diode is as shown:

Zener diodes

• Zener diodes are normal PN junction diodes operating in a reverse-biased condition,
• Working of the Zener diode is similar to a PN junction diode in the forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold/breakdown voltage.
• Zener diodes also called avalanche diodes or Breakdown diodes are the heavily doped P – N junction diodes
• It is operated in a breakdown region,

The symbolic representation of the Zener diode is as shown:

• Photo-diode :
• 1) It is a light-sensing device that is used to sense the intensity of light
• 2) Some of the examples are the smoke detector, a receiver in tv for converting remote signals, etc.
• The symbolic representation of the Photodiode is as shown:

1. A light-emitting diode (LED ):
2. The device which is used to produce the different intensity of light and different color depending upon the types of mater used in making it is called LED.
3. The symbolic representation of the LED is as shown:

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students What is the typical range of the forward voltage of an LED?

1. 5-12 V
2. 1.7-3.3 V
3. 5-12 mV
4. 1.7-3.3 mV

• Explanation:
• LED (light emitting diode):
• The LED (light emitting diode) is a PN junction device which emits light when a current pass through it in the forward direction.
• Materials used:
• Semiconductor materials used for manufacture of LED are gallium arsenide phosphide (GaAsP) which emits red or yellow light or gallium arsenide (GaAs) which gives green or red-light emission.
• Applications:

LEDs are used extensively in segmental and dot matrix displays of numeric and alpha numeric characteristics. Several LEDs are used in series to form one segment while a single LED may be used as a decimal point. Advantages: Size: LEDs are miniature in size and they can be stacked together to form numeric and alpha numeric displays in high density matrix.

• Controlling the output: The light output from an LED is a function of the current flowing through it.
• Therefore, intensity of light emitted from LEDs can be smoothly controlled.
• Efficiency: LEDs have high efficiency as emitters of electromagnetic radiation.
• Power consumption: They require moderate power for their operation.

A typical voltage drop of 1.7 V to 3.3 V and a current of 20 mA is required for full brightness. Therefore, LEDs are useful where miniaturization of DC power is important. Hence option (2) is the correct answer. India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students In LED, light is emitted because:

1. Light falls on LED
2. Recombination of charges takes place
3. PN junction emits light when heated
4. IR light falls on LED
5. none of the above

Option 2 : Recombination of charges takes place

1. In LED, light is emitted due to Recombination of charges takes place.
2. Explanation:
3. LED (light-emitting diode):
4. Basic LED diode is represented as:

• ​ When the diode is forward biased, an electric current starts to flow.
• The majority and minority charge carriers of the P side and N side combine with each other and neutralize the charge carriers in the depletion region.
• This migration releases photon which gives energy in the form of monochromatic light.
• The color of the light emitted has a particular wavelength related to the bandgap energy of semiconductor material as:

E = \(\frac \)

• The selection of emission of color from the LED is fairly limited due to the nature of the semiconductor used.
• Commonly available colors of LED are red, green, blue, yellow, amber and white.

• It is a PN junction device that emits light when a current pass through it in the forward direction, i.e. when LED is forward biased, it emits light.
• When an electron from n-type semiconductor of the diode moves to p-type semiconductor under the influence of an externally applied electric field, it emits a photon with energy equivalent to the energy bandgap of the p-n junction.
• Light-Emitting Diode (LED) : In an LED, this energy lies in the visible region of electromagnetic radiation, and the photon released is perceived as light.
• An LED in this way converts electrical energy into light energy and light is an example of electromagnetic radiation.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students What does LED stand for?

1. Light Emitting Display
2. Low Energy Display
3. Light Emitting Diode
4. Light Emitting Detector

Option 3 : Light Emitting Diode LED stands for Light Emitting Diode. LED (light-emitting diode):

• The LED (light-emitting diode) is a PN junction device that emits light when a current pass through it in the forward direction, i.e. when LED is forward biased, it emits light.
• In an LED, this energy lies in the visible region of electromagnetic radiation, and the photon released is perceived as light.
• An LED in this way converts electrical energy into light energy.
• In reverse biased mode, it works like a normal diode and does not emit light.

• It is an optical semiconductor device that emits light when voltage is applied means it converts electrical energy into light energy.
• When Light Emitting Diode (LED) is forward biased, the free electrons from the n-side and the holes from the p-side are pushed towards the junction.
• Light-emitting diodes emit either visible light or invisible infrared light when forward biased.
• The LEDs which emit invisible infrared light are used for remote controls.
• LEDs that can emit red, yellow, orange, green, and blue light are available for commercial use.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students The value of current limiting resistor for a stack of 4 LED’s connected in series will be _ if the LED’s are 3 V, 3 mA and DC source is 15 V.

• Given:
• Source voltage = 15 V
• Voltage of LED = 3 V
• Current of LED = 3 mA
• Now,
• The given circuit can be drawn as
• The current through the LED circuit must be 3 mA and the voltage drop across them is 3 V each.
• Therefore, by applying KVL, we get,
• 15 – R (3 mA) – 3 – 3 – 3 – 3 = 0
• \(R = \frac } ~k } = 1~k }\)

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students An LED made using GaP emits radiation in _.

1. Visible region
2. Ultraviolet region
3. Infrared region
4. Green radiation

Option 4 : Green radiation

1. LED (light-emitting diode) :
2. The LED (light-emitting diode) is a PN junction device that emits light when a current passes through it in the forward direction.
3. Materials used :
4. Semiconductor materials used for the manufacture of LED are gallium arsenide phosphide (GaAsP) which emits red or yellow light or gallium arsenide (GaAs) which gives green or red-light emission.

Semiconductor material	Wavelength	Colour
GaAs	850 – 940 nm	Infra-red
GaAsP	630 – 660 nm	Red
GaAsP	605 – 620 nm	Amber
GaAsP:N	585 – 595 nm	Yellow
GaP	500 – 570 nm	Green
SiC	430 – 505 nm	Blue
GaInN	450 nm	White
AlGaN	< 400	Ultraviolet

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students

• Study the given figures.
• Identify the elements from 1 to 4 and select the option that shows their correct names

1. 1: Zener diode, 2: Photo diode, 3: LED diode, 4: Junction diode
2. 1: LED diode, 2: Junction diode, 3: Zener diode, 4: Photo diode
3. 1: Photo diode, 2: LED diode, 3: Junction diode, 4: Zener diode
4. 1: Junction diode, 2: Zener diode, 3: Photo diode, 4: LED diode

Option 4 : 1: Junction diode, 2: Zener diode, 3: Photo diode, 4: LED diode PN Junction Diode :

• A unilateral device is a device that conducts only in one direction.
• p-n junction diodes conduct only when the p region is connected to higher voltage and the n region is connected to lower voltage.
• When reverse biased, it acts as an open circuit.
• The symbol for a diode is as shown:

Zener diodes

• Zener diodes are normal PN junction diodes operating in a reverse-biased condition,
• Working of the Zener diode is similar to a PN junction diode in the forward biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its threshold/breakdown voltage.
• Zener diodes also called avalanche diodes or Breakdown diodes are the heavily doped P – N junction diodes
• It is operated in a breakdown region,

1. The symbolic representation of the Zener diode is as shown:
3. Photo-diode :
4. 1) It is a light-sensing device that is used to sense the intensity of light
5. 2) Some of the examples are the smoke detector, a receiver in tv for converting remote signals, etc.
6. The symbolic representation of the Photodiode is as shown:
8. A light-emitting diode (LED ):
9. The device which is used to produce the different intensity of light and different color depending upon the types of mater used in making it is called LED.
10. The symbolic representation of the LED is as shown:

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students The efficiency of an LED for generating light is directly proportional to the

1. applied voltage
2. current injected
3. temperature
4. level of doping.

Option 2 : current injected

• The efficiency of LEDs will be determined by the radiate recombination rate
• Temperature influence the output power of an LED through its effects on the internal quantum efficiency of the device.
• The internal quantum efficiency of LEDs decreasing exponentially with increasing temperature.
• The efficiency of LED is directly proportional to the current injected.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students What is the use of an LED driver?

1. It converts DC to AC
2. It converts AC to DC
3. It converts AC to AC
4. It converts DC to DC

Option 2 : It converts AC to DC An LED driver is a self-contained power supply that regulates the power required for an LED or array of LEDs.

• Constant current LED drivers are designed for a designated range of output voltages and a fixed output current (mA). LEDs that are rated to operate on a constant current driver require a designated supply of current usually specified in milliamps (mA) or amps (A).
• Constant voltage LED drivers are used for LEDs that require one stable voltage and have a current that is already regulated either via simple resistors or an internal constant current driver.

• The output of LED is either constant voltage or constant current (DC).
• LED drivers applications:
• 1) The change in forward voltage of LED with the change in temperature can cause the LED to burn out, this is also known as Thermal Runaway,
• 2) LED drivers prevents damage to LEDs as the constant current LED driver compensates for the changes in the forward voltage while delivering a constant current to the LED.
• 3) Thus LED drivers, convert higher voltage, alternating current to low voltage, direct current, and
• 4) It keeps the voltage or current flowing through the circuit at its rated level.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students In LED, light is emitted because:

1. Light falls on LED
2. Recombination of charges takes place
3. PN junction emits light when heated
4. IR light falls on LED

Option 2 : Recombination of charges takes place

1. In LED, light is emitted due to Recombination of charges takes place.
2. Explanation:
3. LED (light-emitting diode):
4. Basic LED diode is represented as:

• ​ When the diode is forward biased, an electric current starts to flow.
• The majority and minority charge carriers of the P side and N side combine with each other and neutralize the charge carriers in the depletion region.
• This migration releases photon which gives energy in the form of monochromatic light.
• The color of the light emitted has a particular wavelength related to the bandgap energy of semiconductor material as:

E = \(\frac \)

• The selection of emission of color from the LED is fairly limited due to the nature of the semiconductor used.
• Commonly available colors of LED are red, green, blue, yellow, amber and white.

• It is a PN junction device that emits light when a current pass through it in the forward direction, i.e. when LED is forward biased, it emits light.
• When an electron from n-type semiconductor of the diode moves to p-type semiconductor under the influence of an externally applied electric field, it emits a photon with energy equivalent to the energy bandgap of the p-n junction.
• Light-Emitting Diode (LED) : In an LED, this energy lies in the visible region of electromagnetic radiation, and the photon released is perceived as light.
• An LED in this way converts electrical energy into light energy and light is an example of electromagnetic radiation.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students What is the typical range of the forward voltage of an LED?

1. 5-12 V
2. 1.7-3.3 V
3. 5-12 mV
4. 1.7-3.3 mV

• Explanation:
• LED (light emitting diode):
• The LED (light emitting diode) is a PN junction device which emits light when a current pass through it in the forward direction.
• Materials used:
• Semiconductor materials used for manufacture of LED are gallium arsenide phosphide (GaAsP) which emits red or yellow light or gallium arsenide (GaAs) which gives green or red-light emission.
• Applications:

LEDs are used extensively in segmental and dot matrix displays of numeric and alpha numeric characteristics. Several LEDs are used in series to form one segment while a single LED may be used as a decimal point. Advantages: Size: LEDs are miniature in size and they can be stacked together to form numeric and alpha numeric displays in high density matrix.

• Controlling the output: The light output from an LED is a function of the current flowing through it.
• Therefore, intensity of light emitted from LEDs can be smoothly controlled.
• Efficiency: LEDs have high efficiency as emitters of electromagnetic radiation.
• Power consumption: They require moderate power for their operation.

A typical voltage drop of 1.7 V to 3.3 V and a current of 20 mA is required for full brightness. Therefore, LEDs are useful where miniaturization of DC power is important. Hence option (2) is the correct answer. India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students Examples of an active display and a passive display respectively are

1. LCD and Gas discharge plasma
2. LED and LCD
3. Gas discharge plasma and LED
4. Electrophoretic Image display and LED

Electronic visual display :

• An electronic visual display, informally a screen, is a display device for the presentation of images, text, or video transmitted electronically, without producing a permanent record.
• Electronic visual displays include television sets, computer monitors, and digital signage,

The electronic visual display is classified into three types:

• Analog or Digital
• Active displays
• Passive displays

Active displays :

• If the visual information is presented by emitting light then that is called “Active displays”.
• A special feature for front panel receiver displays that generates animated patterns for both segmented and dot-matrix LCDs that proceed the sequential display of information such as a clock, CD titles
• Examples: CRT, LED’s, VFD, SED

Passive displays : If the visual information is presented by modulating light then that is called “Passive displays”. Examples: Liquid Crystal Displays, Digital Micromirror Device (DMD), Interferometric modulator(IMOD). India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students Which of the following LED colours is NOT present in an LED TV panel?

1. 1) A LED display is a flat panel display that uses an array of light-emitting diodes as pixels for a video display.
2. 2) LED displays can offer higher contrast ratios than a projector and are thus an alternative to traditional projection screens.
3. 3) LED display consists of a matrix of red, green, and blue diodes.
4. ∴ Option 2 is the correct choice.

India’s #1 Learning Platform Start Complete Exam Preparation Daily Live MasterClasses Practice Question Bank Mock Tests & Quizzes Trusted by 3.4 Crore+ Students : LED MCQ – Objective Question Answer for LED Quiz – Download Now!

What semiconductor is used in LEDs?

What is an LED? In the simplest terms, a light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it. Light is produced when the particles that carry the current (known as electrons and holes) combine together within the semiconductor material.

• Since light is generated within the solid semiconductor material, LEDs are described as solid-state devices.
• The term solid-state lighting, which also encompasses organic LEDs (OLEDs), distinguishes this lighting technology from other sources that use heated filaments (incandescent and tungsten halogen lamps) or gas discharge (fluorescent lamps).

Different colors Inside the semiconductor material of the LED, the electrons and holes are contained within energy bands. The separation of the bands (i.e. the bandgap) determines the energy of the photons (light particles) that are emitted by the LED.

1. The photon energy determines the wavelength of the emitted light, and hence its color.
2. Different semiconductor materials with different bandgaps produce different colors of light.
3. The precise wavelength (color) can be tuned by altering the composition of the light-emitting, or active, region.
4. LEDs are comprised of compound semiconductor materials, which are made up of elements from group III and group V of the periodic table (these are known as III-V materials).

Examples of III-V materials commonly used to make LEDs are gallium arsenide (GaAs) and gallium phosphide (GaP). Until the mid-90s LEDs had a limited range of colors, and in particular commercial blue and white LEDs did not exist. The development of LEDs based on the gallium nitride (GaN) material system completed the palette of colors and opened up many new applications.

Indium gallium nitride (InGaN): blue, green and ultraviolet high-brightness LEDs Aluminum gallium indium phosphide (AlGaInP): yellow, orange and red high-brightness LEDs Aluminum gallium arsenide (AlGaAs): red and infrared LEDs Gallium phosphide (GaP): yellow and green LEDs

: What is an LED?

Why is compound semiconductor used in the making of an LED?

1 Compound Semiconductors for Microsystems – Compound semiconductor microsystems have become an emerging technology because of their unique intrinsic properties, which offer a number of materials-based advantages for optoelectronic and sensing applications.

The intrinsic properties of these materials such as direct or indirect band gap, variation of band gap (from zero via narrow to wide), piezoelectricity, piezoresistivity, variable thermal conductivity, higher saturation velocity of electrons, operation at high temperature and high frequencies make them superior to the well-developed silicon technology.

The zincblende structure of most common compound semiconductors allows piezoelectricity, which leads to interesting sensing applications. The compound semiconductor materials allow monolithic integration of optoelectronic devices such as lasers, light-emitting diode (LEDs), and photodiodes with micromechanical structures.

1. This enables light generation, transmission, modulation, and detection on a single chip.
2. Furthermore, epitaxially grown single-crystalline compound semiconductor layers give rise to well-controlled mechanical characteristics.
3. The epitaxial advantage also facilitates the growth of monolithic multilayers with ternary and quaternary alloys, enabling precise lattice matching.

This introduces a wide variety of heterostructure-based physical effects for microsystems. The monolithic multilayers can be selectively etched to release the mechanical structures, as the compound semiconductors are very rich in chemistry. Micromachining on compound semiconductors has been successfully applied to fabricate cantilevers, membranes, waveguide switches, radio frequency (RF) inductors, microbolometers, micromotors, wavelength-tunable microcavity devices such as optical filters, optical amplifiers, vertical cavity surface-emitting lasers (VCSELs), LEDs, and photodiodes.

• Diverse nature of compound semiconductors provides numerous possibilities to design various material compositions.
• However, compounds from group III–V (gallium arsenide (GaAs)-, indium phosphide (InP)-, and nitride-based materials) and compounds from group IV (SiGe and SiC materials) have been used for microsystems due to their material properties, which is required for the present technological advances.

The structural and mechanical properties of these materials are listed in Table 1, Dielectric material-based micromechanical structures with group II–VI compound semiconductors have also been investigated for (hybrid) microsystems by Keating et al, (2006),

	GaAs	InP	GaN	Si 1− x Ge x	3C-SiC
Crystal structure	Zincblende	Zincblende	Zincblende/wurtzite	Diamond (random alloy)	Zincblende
Lattice constant (Å)	5.6533	5.8687	4.52/a-3.189 c-5.18	(5.431+0.20 x +0.027 x 2 )	4.3596
Density (g m −3 )	5.317	4.81	6.15	(2.329+3.493 x −0.499 x 2 )	3.21
Melting point (°C)	1240	1060	2500	Solidus	2830
				1412−738 x +263 x 2
Specific heat (J g −1 °C −1 )	0.33	0.31	0.49	0.4075 at x =0.75	0.69
				0.505 at x =0.50
				0.6025 at x =0.25
Thermal conductivity (W cm −1 °C −1 )	0.55	0.68	1.3	(0.046+0.084 x )	3.6
Thermal expansion coefficient (10 −6 °C −1 )	5.73	4.6	α ∥ =α a =5.59/α ort =α c =3.17	2.6+2.55 x ( x <0.85)	3.8
				7.53−0.89 x ( x >0.85)
Debye temperature (K)	360	425	600	640−226 x	1200
Elastic constants (10 11 dyn cm −2 )
C 11	11.90	10.11	29.3/39.0	16.58−3.73 x	35.23
C 12	5.38	5.61	15.9/14.5	6.39−1.56 x	14.04
C 44	5.96	4.56	15.5/10.5	7.96−1.28 x	23.29
Young’s modulus (Y o ) 10 11 dyn cm −2	8.59	6.11	18.1	13.02−28.1 x	74.8
Piezoelectric constant (C m −2 )	e 14 =−0.16	e 14 =−0.035	e 14 =0.4/ e 15 =−0.30/ e 31 =−0.33/ e 33 =0.65	e 14 =−0.0114 at x =0.2	e 15 =0.08 e 33 =0.20

GaAs-based materials are most extensively studied for optoelectromechanical devices in compound semiconductors as is silicon in semiconductors. The GaAs-based materials are promising for the fabrication of integrated sensors because of their direct band gap, high piezoelectricity, piezoresistivity, and thermoelectricity properties, which are used as a light source and detectors, dynamic and static pressure and temperature sensors, respectively ( Hjort et al,, 1994b ). These materials also take advantage of GaAs/aluminum gallium arsenide (AlGaAs) material systems, which can be monolithically grown with lattice matching, and either one of them can be selectively etched to create microstructures. The possibility of semi-insulating GaAs material facilitates easy separation of the individual devices of a circuit, which enables high-speed performance of field-effect transistors (FETs) and MEMS for the development of monolithic microwave-integrated circuit (IC) on a single chip. Thermal conductivity of GaAs is three times lower than that of silicon and thus has a better prospect of meeting the requirement for maximum thermal resistance. In GaAs, the physical mechanisms that change the resistance due to an applied stress are different from that of silicon. AlGaAs is a very interesting semiconductor with piezoelectric properties for force and resonant sensors, with high Seebeck coefficients for infrared thermopile sensors, and with a wide energy gap, when compared to silicon and GaAs, for high-temperature sensors ( Dehé et al,, 1995 ). Thus, excellent bolometric infrared sensors have been realized using suspended AlGaAs membranes. Recently, strain-driven, self-assembled 3D micro/nanostructures have also been fabricated on GaAs-based materials ( Prinz et al,, 2001 ). Because of all these features, GaAs-based materials meet the special requirements of integrated microoptoelectromechanical systems (MOEMS) for various applications. Micromachining on InP closely resembles the techniques used for GaAs. Many of the properties of InP are similar to GaAs in terms of crystal structure and mechanical properties ( Greek et al,, 1999; Pruessner et al,, 2003 ). However, the band gap of InP-based materials make them the promising candidate for light source of optical fiber communication systems because of low loss and low dispersion at 1.3 and 1.5 µm wavelengths. Micromachined InP/air gap distributed Bragg reflector (DBR)-based tunable vertical cavity devices such as filters, VCSELs, and photodiodes are attracting much interest because of their unique features of a wide continuous wavelength tuning and 2D array integration, thus making it possible to realize dense wavelength division multiplexing (DWDM) systems on InP. Recently, some efforts have been directed toward employing wider band gap compound semiconductor materials such as gallium nitride (GaN; Davies et al,, 2004 ; Strittmatter et al,, 2001 ; Yang et al,, 2006 ) and SiC ( Mehregany and Zorman, 2004 ) for microsystems owing to their excellent electrical and mechanical properties with regard to chemical inertness and their high-temperature stability, which make them a suitable choice for MEMS applications in harsh environments. Polysilicon is widely used for surface-micromachined MEMS structures with silicon IC compatibility, which needs high-temperature processing (>800°C). An alternative low-temperature processing material is poly-SiGe. Micromachined bolometers and thermopiles with superior thermoelectric properties have been fabricated using poly-SiGe by Dong et al, (2003), Freestanding SiGe micro/nanostructures such as tubes, helical coils, and bridges have also been fabricated on SiGe ( Prinz et al,, 2001 ). Microsystems have been successfully implemented on compound semiconductors; however, there is a skepticism with regard to the mechanical strength of some of the III–V compound semiconductors such as GaAs- and InP-based materials for microstructures. However, measured fracture properties of GaAs are shown to be sufficiently enough, with an average fracture strength of 2.7 GPa, which is at least three times as high as that of most construction steels ( Hjort et al,, 1994a ). Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128035818092353

Which semiconductor is used in LED Class 12?

Hint: A light emitting diode is a semiconductor device which propagates or throws light around, for the device to throw light around current must flow through it. Earlier the LED’s could only produce red colour but nowadays they can produce a variety of colours.

Complete step by step solution: LED works on the principle of a Quantum Theory. The quantum theory states that when the energy of electrons which are present in the semiconductor decreases from the higher level to a lower level, it emits energy which is in the form of photons. The larger the gap the more energy the photons will have.

The recombination of the electrons shows that they move from conduction band to valence band and emits an energy which is electromagnetic in nature and is in the form of photons. The preferred semiconductors that are used in making the LED are Gallium Arsenide, Gallium phosphide or the combination of the two Gallium arsenide phosphide.

1. The different materials of the semiconductors and doped with different impurities results in different colours from LED.
2. LED’s are highly energy efficient and use 90% less energy than the lower power incandescent bulbs.
3. It dramatically decreases power costs and also the LED’s are more luminous than the bulbs because most of the power of the bulb goes waste as heat.

Note: LEDs are one of the most ubiquitous products today thanks to their power efficiency, cost reduction, easy maintenance etc. It was only recently that the elusive blue LED was made. Scientists have developed a technique for producing multiple colours from a single LED.

Which of the following material is used to make LED Mcq?

Answer (Detailed Solution Below) – Option 2 : Gallium arsenide phosphide Free 10 Questions 20 Marks 12 Mins The LED (light-emitting diode) is a PN junction device that emits light when a current passes through it in the forward direction. Materials used : Semiconductor materials used for the manufacture of LED are gallium arsenide phosphide (GaAsP) which emits red or yellow light or gallium arsenide (GaAs) which gives green or red-light emission.

Applications : LEDs are used extensively in segmental and dot matrix displays of numeric and alphanumeric characteristics. Several LEDs are used in series to form one segment while a single LED may be used as a decimal point. Advantages : Size: LEDs are miniature in size and they can be stacked together to form numeric and alphanumeric displays in a high-density matrix.

Controlling the output: The light output from an LED is a function of the current flowing through it. Therefore, the intensity of light emitted from LEDs can be smoothly controlled. Efficiency: LEDs have high efficiency as emitters of electromagnetic radiation.

1. Available colors: LEDs are available in different colors like red, green, yellow, and amber.
2. Switching time: The switching time of both ON and OFF is less than 1 ns and therefore they are very useful where the dynamic operation of a large number of arrays is involved.
3. Economical and Reliable: LEDs are manufactured with the same type of technology as is used for transistors and ICs and therefore they are economical and have a high degree of reliability.

Operating temperature: LEDs are rugged and can, therefore, withstand shocks and vibrations. They can be operated over a wide range of temperature 0 to 70°. Last updated on Dec 5, 2022 UPSC IES 2021 Reserve List Released.28 candidates have been recommended in this list to fill up the vacancies.

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Is silicon used in LED?

Answer (Detailed Solution Below) – Option 1 : An indirect band gap semiconductor Free ST 1: Basic Electrical Engineering 20 Questions 20 Marks 20 Mins Explanation: LED (light-emitting diode): Basic LED diode is represented as:

• The selection of emission of color from the LED is fairly limited due to the nature of the semiconductor used.
• Commonly available colors of LED are red, green, blue, yellow, amber, and white.

• Light Emitting Diode (LED) works on the principle of Electroluminescence.
• It is the conversion of electrical energy into light energy,
• In LED, most of the light is concentrated near the junction because charge carriers will be very close and less than the diffusion length.
• LEDs are generally fabricated with Direct Band Gap (DBG) semiconductors like GaAs, GaAsP, GaP.

Direct Band Gap (DBG) Semiconductors: The semiconductor in which the top of the valence band and the bottom of the conduction band occur at the same value of momentum. Since Silicon is an Indirect Band Gap semiconductor so electron cannot fall directly to the valence band but must undergo a momentum change as well as a change in energy. So, energy is released as heat along with the light. Hence, silicon is not suitable for the fabrication of LEDs. Important Points Band Gap : The minimum energy difference between the top of the valence band and the bottom of the conduction band is known as the bandgap. Indirect Band Gap Semiconductor : In the (IBG) semiconductor, the maximum energy of the valence band occurs at a different value of momentum to the minimum in the conduction band energy.

Examples: Silicon and Germanium. Note : Modern LEDs can be fabricated with some of the IBG semiconductors but under controlled doping. Latest UPMRC Station Controller Updates Last updated on Sep 26, 2022 The Uttar Pradesh Metro Rail Corporation (UPMRC) released UPMRC Station Controller Psycho Aptitude Test Admit Card on 15th June 2021.

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Why silicon is used in LED?

Silicon’s dark secret – Light-emitting diodes are as cheap as chips, but they aren’t made from silicon. Why? Because silicon doesn’t like to emit light. Semiconductors at a general level are all the same. Electrons can exist in the valence band, where they are stuck bound to a local atom, or they can be in the conduction band, where they are free to move around.

1. For an electron to go from the valence to the conduction band, it needs to acquire energy greater than the energy difference between the valence and conduction bands.
2. When an electron drops from the conduction band to the valence band, it must lose that energy.
3. In a light-emitting diode, electrons drop out of the conduction band by losing energy in the form of light.

And, importantly, they can do this in a single step. In silicon, electrons have to emit a photon and a sound vibration (a phonon) at the same time to reach the valence band. Instead, the electron typically finds a way to lose the energy without emitting a photon, so no light comes out.

Is silicon suitable for LEDs?

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Why silicon and germanium can be used in LED?

Light Emitting Diode Structure LEDs are p-n junction devices constructed of gallium arsenide (GaAs), gallium arsenide phosphide (GaAsP), or gallium phosphide (GaP). Silicon and germanium are not suitable because those junctions produce heat and no appreciable IR or visible light.

Which semiconductor is not used in LED?

Because the energy released by combination of holes and electrons in elemental semiconductors does not lie in the visible spectrum, elemental semiconductor cannot be used to make visible LED’s.

Why silicon and germanium Cannot be used in LED fabrication?

Answer : As energy band gap E for both Si and Ge is less than 18 eV, they will emit only infrared radiation.

Are LEDs made of semiconductors?

A light-emitting diode (LED) is a semiconductor device that emits light when a forward voltage is applied to it. The fact that certain semiconductors emit light has been observed by a number of semiconductor researchers from early on. After it was successfully demonstrated in 1960 that ruby could be used as a source of laser, inspired researchers sought to produce laser beams using the electroluminescence effect of semiconductors.

• At the time, compound semiconductors based on gallium arsenide (GaAs) and other materials were attracting greater attention than silicon-based semiconductors.
• Since GaAs is superior to silicon in terms of electric properties at high frequencies, it was considered to be suitable for laser applications, too.

After a fierce competition among researchers, three American teams separately conducted successful experiments on LEDs in 1962.

Why gallium arsenide is used in LED?

GaAs devices generate less noise than most other types of semiconductor components. This is important in weak-signal amplification. Gallium arsenide is used in the manufacture of light-emitting diode s (LEDs), which are found in optical communications and control systems.

What type of material first used a LED light?

LEDs and OLEDs S mall lights with big potential: light emitting diodes & organic light emitting diodes Commercial History (1960s – Today) Introduction: The LED is a light source which uses semiconductors and electroluminescence to create light. There are two major kinds of light emitting diodes: LED and OLED,

• The LED is different than EL lamp in that it uses a small semiconductor crystal with reflectors and other parts to make the light brighter and focused into a single point.
• The OLED is very similar to the EL lamp in design, using a flat sandwich of materials.
• It is different than the LED and EL lamp in that it uses organic (carbon) molecules in the layer that emits light.

All credits and sources are located at the bottom of each lighting page

Our video on LEDs and OLEDs, click the bracket icon on the lower right to expand size: LEDs Currently the LED lamp is popular due to it’s efficiency and many believe it is a ‘new’ technology. The LED as we know it has been around for over 50 years. The recent development of white LEDs is what has brought it into the public eye as a replacement for other white light sources.

Large LED array designed for use as a street lamp. A massive aluminum heat sink is needed with the high wattage LEDs

Advantages: -Energy efficient source of light for short distances and small areas. The typical LED requires only 30-60 milliwatts to operate -Durable and shockproof unlike glass bulb lamp types -Directional nature is useful for some applications like reducing stray light pollution on streetlights Disadvantages: -May be unreliable in outside applications with great variations in summer/winter temperatures, more work is being done now to solve this problem -Semiconductors are sensitive to being damaged by heat, so large heat sinks must be employed to keep powerful arrays cool, sometimes a fan is required. This adds to cost and a fan greatly reduces the energy efficient advantage of LEDs, it is also prone to failure which leads to unit failure -Circuit board solder and thin copper connections crack when flexed and cause sections of arrays to go out -Rare earth metals used in LEDs are subject to price control monopolies by certain nations -Reduced lumen output over time

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LED Statistics *Lumens per watt: 28 – 150 (depends on environment) *Lamp life: 25,000 – 100,000 hours *CRI (White LEDs) – 70 *Color Temperature (White LEDs) – 2540 – 10,000K *Available in 0.01 – 3 W Left: White LEDs became an affordable commercial product in the 2000s

1. HOW THEY WORK LEDs create light by electroluminescence in a semiconductor material, Electroluminescence is the phenomenon of a material emitting light when electric current or an electric field is passed through it – this happens when electrons are sent through the material and fill electron holes.

1. An electron hole exists where an atom lacks electrons (negatively charged) and therefore has a positive charge.
2. Semiconductor materials like germanium or silicon can be “doped” to create and control the number of electron holes.
3. Doping is the adding of other elements to the semiconductor material to change its properties.

By doping a semiconductor you can make two separate types of semiconductors in the same crystal. The boundary between the two types is called a p-n junction. The junction only allows current to pass through it one way, this is why they are used as diodes. Above: A 5 Watt LED, one of the most powerful LEDs available. Above: A laser also creates light, but through a different construction. Read more about semiconductor devices used in electronics here. To understand p-n junctions and semiconductors better you will need to invest a good amount of time in a lecture, it is not a simple phenomena and far too lengthy to cover here. See a 59 minute introduction lecture to solid state (semiconductors) here, Phosphors are used to help filter the light output of the LED. They create a more pure “harsh” color. Engineers had to figure out how to control the angle the light escapes the semiconductor, this “light cone” is very narrow. They figured out how to make light refract or bounce off all surfaces of the semiconductor crystal to intensify the light output. Above: various colors of LEDs on display at the Edison Tech Center. The metal tabs on the sides of each help distribute the heat away from the LED. Photo: Whelan Communications, Peter Heppner at the MTV music awards, Bucharest, Romania Above: A “Jumbotron” or full color LED display. This type of display is only usable for large area applications and decorative backgrounds in small spaces. The human eye can only effectively perceive the image at more than 6 meters distance. Above: Two different types of LEDs, both in a strip mount configuration 2. INVENTORS AND DEVELOPMENTS

The First LED: Above: this experiment of a tunnel diode atop a GaAs semi-insulating substrate convinced Pittman and Biard that there must be light emission going on, and resulted in further experimentation.

The early years of the 1960s consisted of a ‘race’ in the field of semiconductors. Gallium arsenide and germanium were some of the first semiconductors uses before silicon became the preferred material in the industry. Engineers were experimenting with p/n junctions, These devices were being developed as diodes since they can pass current in one direction by not the other. GE, Bell Labs,Lincoln Labs, RCA research labs, and Texas Instruments worked to develop semiconductors for power control and laser technology. It was in this race that the LED was ‘discovered’ in the Fall of 1961 by James R. Biard and Gary Pittman. Gary had been working in the related field of solar cells since 1958. In their efforts to try to make an X-band GaAs varactor diode they created tunnel diodes (which had been developed first at Esaki). They placed the tunnel diode on a GaAs substrate and discovered that there must be light production going on during forward bias operation. Using an infrared detector just brought in from Japan they tested it and discovered that the devices lit up brightly! Soon after this others made discoveries in the field, however TI was the first to get a patent and sell the first LED for $130 each. The SNX-100 was the first LED sold (summer of 1962). The LEDs were first used with IBM computers to replace tungsten bulbs that controlled punch card readers (infrared light was sent through the holes, or blocked by the card). Today there is a myriad of applications for the LED. The First LED patent ( click to enlarge ) You can clearly see the p/n junction in the patent drawing. The p/n junction is a single crystal with two types of semiconductors created by doping.

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Above: 1958: Walter T. Matzen (top) and Bob Biard (bottom) worked on parametric amplifiers, this helped lay groundwork for the LED. Later Gary Pittman and Mr. Biard worked on varactor diodes which led to the LED as we know it. Read the full story of their work with this PDF here. * 1972: Herbert P. Maruska & Jacques Pankove developed the violet LED which set the stage for development of a bright blue LED in 1993 Photos: Randy Lamb, UC Santa Barbara / Semicon West 2012 / PD-USGOV / Bob Biard

	1907 – H.J. Round discovered electroluminescence when using silicon carbide and a cats whisker. Oleg Losev independently discovered the phenomena the same year. London, United Kingdom
	1920s – Oleg V. Losev studied the phenomena of light emitting diodes in radio sets. His first work on ‘LEDs’ involved a report on light emission from SiC. In 1927 he published a detailed report but his work was not well known until the 1950s when his papers resurfaced. Saint Petersburg, Russia
	1961 – James R. Biard. “Bob” Biard and Gary Pittman developed the Infrared LED at Texas instruments. This was the first modern LED. It was discovered by ‘accident’ while TI tried to make an X-band GaAs varactor diode. The discovery was made during a test of a tunnel diode using a zinc diffused area of a GaAs (Gallium Arsenide) semi-insulating substrate. Dallas, Texas Photo: Robert Biard
	1961 – Gary Pittman worked together with James R. Biard. He had started working in 1958 with semiconductor GaAs for the creation of early solar cells. He discovered and developed the infrared LED with James R. Biard. Dallas, Texas
	1962 – Nick Holonyack Jr. develops the red LED, the first LED of visible light. He used GaAsP (Gallium Arsenide Phosphide) on a GaAs substrate. General Electric. Syracuse, New York Photo: PD-USGOV
	1972 – M. George Craford creates the first yellow LED at Monsanto using GaAsP. He also develops a brighter red LED. St. Louis, Missouri Photo: Semicon West 2012
	1972 – Herbert Maruska and Jacques Pankove develop the violet LED using Mg-doped GaN films, The violet LED is the foundation for the true blue LED developed later. RCA Labs, New Jersey
	1979 – Shuji Nakamura develops the world’s first bright blue LED using GaN (Gallium nitride). It wouldn’t be until the 1990s that the blue LED would become low cost for commercial production. Tokushima, Japan Photo: Randy Lamb, UC Santa Barbara
	1976 – Thomas P. Pearsall develops special high brightness LEDs for fiber optic use. This improves communications technology worldwide. Paris, France Photo: T.P. Pearsall

OLED: Organic Light Emitting Diodes What is an OLED? The Organic LED is made of a layer of organic electroluminescent material with p/n junction sandwiched between to electrodes. At least one of the electrodes is transparent so the photons can escape.

1. Similar to an EL lamp, current is passed through a semiconductor (like the phosphor in an EL lamp), however the difference is that an OLED uses a p/n junction were there is a recombination of p and n carriers.
2. EL (TDFEL, TFEL, powder EL) technology only uses a material excited by current to make light.

The semiconductor in an OLED is organic which means it contains carbon. The OLED uses one of two kinds of compounds: polymers or ‘small molecule’, Read more about how it works below. Uses: Lamps – short distance indoor lamps (produces a diffused light) Displays – small: phones and media devices and large: televisions, computer monitors Advantages: -The units are lighter than traditional LEDs and can be made thinner as well -OLEDs can provide a more energy efficient alternative to LCD computer and television monitors -Can be used in a myriad of new applications in which lighting technology has never been used before Disadvantages: -The cost of OLEDs is still high and each unit produces less lumens than a normal LED -The technology is still under development so the life of the OLED is being researched as new materials are used and tested each year.

OLED Statistics *Lumens per watt: up to 50 in lamps (as of 2/2012) *Lamp life: still under research *CRI (White OLEDs) – still under research *Color Temperature (White LEDs) – various whites are in development *Available wattage: N/A

Patent by OLED co-inventor Stephen Van Slyke Displays (computer monitors, televisions, mobile phone screens): The OLED display is made by using multiple layer construction along with transistors which control whether each pixel is on or off. This is very similar to EL displays.

• The OLED display has the potential to be more efficient and thinner than the LCD.
• One advantage is that does not need a cold cathode fluorescent backlight like an LCD.
• The lack of a backlight means it can better display blacks (the back light always seeps through in black areas of the screen).
• The OLED display can also provide better contrast ratios than an LCD,

The OLED display may also be made into a thin flexible material which could roll up like a newspaper. Currently the OLED is not as bright as EL or LCD displays it works better in areas with less ambient light. That may change as engineers work to increase luminosity. The diagram above is a simple modern OLED. There are a many new ways to construct the OLED using a variety of layer configurations. Displays will have additional layers such as an active matrix TFT (thin film transistor) which control pixel regions. How the OLED Works: Layers: Early OLEDs had one layer of organic material between two electrodes.

1. Modern OLEDs are bi-layer, they have an emissive layer and conductive layer sandwiched between two electrodes (see diagram above).1.
2. Electric current passes from the cathode to the anode.
3. It passes through two layers of organic molecules.2.
4. The first layer the electrons pass into what is called the emissive layer,

Electrons leave the conductive layer making ‘holes’ (positive charge). Meanwhile in the emissive layer there are excessive electrons (negative). The ‘holes’ jump to the emissive layer along the border of the two layers where they recombine with electrons (this place is the p/n junction). Photo: Wikipedia: Tobias G. Types of OLEDs: LEC – Electrochemical Cell – this has ions added to the OLED PMOLED – Passive-matrix OLED – the first display technology, developed in the mid 90s AMOLED – Active-matrix OLED – used in displays, it has a switch built into it in the form of a thin film transistor backplane.

The transistor allows the unit to be switched on and off. PLED – polymer LED Polymer LEDs use a plastic to emit light. They have the properties of semiconductors yet are versatile and low cost to produce. The layers that emit light are similar to an ink and will be very cheap to manufacture once stable compounds and processes are developed.

Deeper understanding of these improvements requires a basic background in chemistry and physics, you also can read more detail here, The Future: OLEDs will allow for thinner TV and computer displays, transparent “heads up” displays, flexible displays, flat roll-on surface lights on the sides of buildings or vehicles, changing camouflage displays for military vehicles, new photovoltaic applications, and much more. OLED Inventors and Developments:

	1979, 1987 – Ching Tang discovers that he can create light by sending current through a carbon material. Steven Van Slyke and Tang built the first OLED at Kodak in 1987. Later he works on an OLED displays. His first light was a bright green light at 10 volts. Ching Tang continues to work on OLEDs at the University of Rochester. Rochester, New York Photo: University of Rochester
	1979, 1987 – Steven Van Slyke worked with Ching Tang on the first OLEDs at Kodak. Kodak becomes a patent holder of SMOLED (small-molecule OLED) technology. SMOLED requires depositing organic molecules in a vacuum. This is a very expensive process at the time. Rochester, New York Photo: Steven Van Slyke
	1988 – Chihaya Adachi invented electron transport materials and constructed a double heterostructure OLED which has been widely used in present OLEDs. Since 1988, his research has been focusing on material development and device physics. Recently he invented 3rd generation light emitting materials, TADF, enabling efficient EL. Read from his papers Fukuoka, Japan Photo: Chihaya Adachi
	1988 – Tetsuo Tsutsui contributed much to the development of high-performance OLEDs through the proposals of design concept on multilayer OLEDs in 1988, the concept of carier balance in 1992, and the usage of the optical microcavity effect in 1993. Testuo Tsutsui with Prof. Shogo Saito made many contributions to the commercialization of small-size OLED displays by Pioneer, TDK and Sanyo Electric in Japan. Fukuoka, Japan Photo: Prof. Tetsuo Tsutsui
	1990 – Jeremy Burroughes along with Richard Friend and Donal Bradley discover polymer based OLEDs, this reduced cost of production to marketable levels. PLED (polymer LED) technology competes with SMOLED for the future of OLEDs. Cambridge University Cavendish Laboratory.

Which metal is used in LED?

Abstract – The use of light-emitting diodes (LEDs) is expanding because of environmental issues and the efficiency and cost savings achieved compared with use of traditional incandescent lighting. The longer life and reduced power consumption of some LEDs have led to annual energy savings, reduced maintenance costs, and lower emissions of carbon dioxide, sulfur dioxide, and nitrogen oxides from powerplants because of the resulting decrease in energy consumption required for lighting applications when LEDs are used to replace less-energy-efficient sources.

• Metals such as arsenic, gallium, indium, and the rare-earth elements (REEs) cerium, europium, gadolinium, lanthanum, terbium, and yttrium are important mineral materials used in LED semiconductor technology.
• Most of the world’s supply of these materials is produced as byproducts from the production of aluminum, copper, lead, and zinc.

Most of the rare earths required for LED production in 2011 came from China, and most LED production facilities were located in Asia. The LED manufacturing process is complex and is undergoing much change with the growth of the industry and the changes in demand patterns of associated commodities.

In many respects, the continued growth of the LED industry, particularly in the general lighting sector, is tied to its ability to increase LED efficiency and color uniformity while decreasing the costs of producing, purchasing, and operating LEDs. Research is supported by governments of China, the European Union, Japan, the Republic of Korea, and the United States.

Because of the volume of ongoing research in this sector, it is likely that the material requirements of future LEDs may be quite different than LEDs currently (2011) in use as industry attempts to cut costs by reducing material requirements of expensive heavy rare-earth phosphors and increasing the sizes of wafers for economies of scale.

• Improved LED performance will allow customers to reduce the number of LEDs in automotive, electronic, and lighting applications, which could reduce the overall demand for material components.
• Non-Chinese sources for rare earths are being developed, and some of these new sources are likely to be operational in time to meet increasing demand for rare earths from the LED sector.

Because most LED component production and manufacturing occurs in Asia and many LED producers have established supply contracts with Chinese producers of rare earths, a significant amount of the metallic gallium, indium, and the rare earths used for LED production will likely continue to come from Chinese sources at least for the next 5 years; however, a greater amount of these materials are now being processed in Japan, the Republic of Korea, and Taiwan.

• As non-Chinese sources of rare earths come into production, these new mines are likely to be sources of light REEs, but China will likely remain the leading source of supply for the heavy REEs suitable for use as LED dopants and phosphors at least for the next few years.
• Increased research in the development of phosphors that use smaller amounts of or different REEs is intended to reduce dependence on rare earths from China.

Supply disruption of rare earths and other specialty metals could take place if China’s specialty metal exports are redirected to domestic markets. The cost of recovery is high and the lifespan for LEDs is comparatively long; thus, the LED waste volume was low in 2010, and few LEDs were recycled.

The minute metal content of LEDs leads to a high cost for recovery, so recycling of LEDs outside of electronic waste is unlikely in the near term, although some LED producers are evaluating recycling options. Recycling of metals from LEDs in electronic waste is possible if the costs of recovering metals are justified by demand and metal prices.

First posted November 26, 2012

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Wilburn, D.R., 2012, Byproduct metals and rare-earth elements used in the production of light-emitting diodes—Overview of principal sources of supply and material requirements for selected markets: U.S. Geological Survey Scientific Investigations Report 2012–5215, 15 p., available only at http://pubs.usgs.gov/sir/2012/5215/. Sources and Supplies of Selected Mineral Commodities Used in Light-Emitting Diodes

Which of the following material is most suitable for making LEDs?

Some metals that are used in L.E.D are arsenic, indium as well as gallium. The compound that is used for making LED is Gallium arsenide phosphide ( GaAs 1 – x P x ).

What is the raw material of LED?

Jameson Simpson Mounting and Slicing To start the process, a tiny piece of silicon carbide (SiC), called a seed, is mounted in a crucible that is also filled with SiC. Heat is applied in a furnace and the SiC turns into a vapor that deposits on the seed to form a large crystal called an ingot. Jameson Simpson Polishing Each wafer is buffed into a smooth finish and the surface is washed and dried in preparation for LED fabrication. Washing can also happen after elements are baked onto (see step three) depending on the type of LEDs being produced. Jameson Simpson Depositing and Dicing Indium, gallium, and nitrogen are baked onto the wafer to form the active layer of the future LED. The wafer is transferred to another machine where it is diced into as many as 100,000 tiny LED chips. When voltage is applied to a chip, electrons and holes form and recombine in the active layer to produce light, generally blue or green in color. Jameson Simpson Binning Each LED chip on a wafer is lit to check for brightness and color point. They are then sorted into bins. Each bin is a sheet of sticky film onto which the sorted chips are organized into neat rows. The bins then are manually inspected again for quality control. Jameson Simpson Finishing The LED chip then is glued onto a package where phosphor is added. Some of the blue light generated by the LED chip is converted by the phosphor to other colors such as red and yellow. These new colors combine with the remaining blue light to create white light.

What type of semiconductor is used in LED electronic circuits Mcq?

Here are 1000 MCQs on Electronic Devices and Circuits (Chapterwise),1. Which of the following is not an electronic device? a) A mobile b) A computer c) A magnifying glass d) A keyboard View Answer Answer: c Explanation: A mobile, a computer and a keyboard are electronics devices because they are controlled by the flow of electrons for information processing. A magnifying glass is a non-electronic device.2. Which of the following is not a physical component of an electronic circuit? a) Capacitor b) Inductor c) Diode d) Temperature View Answer Answer: d Explanation: Capacitors, inductors, and diodes are the physical components of electronic circuits because they affect the flow of electrons or current in the circuit.3. Which of the following is not a property of semiconductors used in electronic devices? a) They excite electrons b) They don’t emit light c) They have high thermal conductivity d) They have variable electrical conductivity View Answer Answer: b Explanation: Semiconductors excite electrons. They have variable electrical conductivity and high thermal conductivity. Some compound semiconductors also emit light which is popularly known as light-emitting diodes.4. Which of the following is the correct relationship between temperature (T) and mobility (u) of electrons in electronic circuits? a) u ∝ T -3/2 b) u ∝ T -1/2 c) u ∝ T d) u ∝ T -1 View Answer Answer: a Explanation: When temperature increases then the frequency of the lattice point increases and as a result collisions of electrons increases. Hence, mobility decreases. The correct relation is u ∝ T -3/2,5. What is the effect of temperature on the recombination rate of electrons in electronic circuits? a) Recombination rate increases with increase in the temperature b) Recombination rate decreases with increase in the temperature c) Recombination rate is independent of temperature c) Recombination of electrons doesn’t occur in semiconductors View Answer Answer: b Explanation: Recombination rate decreases when temperature increases because the electrons that are going to combine with holes in the valence bond are re-excited.6. Which of the following is correct about semiconductors in electronic devices? a) Elemental semiconductors have direct band gap b) Compound semiconductors have indirect band gap c) Extrinsic semiconductors are injected with impurities d) Doping is done in Intrinsic semiconductors View Answer Answer: c Explanation: Elemental semiconductors have indirect band gap. Compound semiconductors have direct band gap. Doping is done with impurities in extrinsic semiconductors, not in intrinsic semiconductors.7. Which of the following technique can’t be used for generating electron-hole pairs in electronic devices? a) Thermal excitation b) Impact ionization c) Photo excitation d) Impurity injection View Answer Answer: d Explanation: Electron-hole pairs can be generated by increasing temperature or ionization or photo excitation. Impurity injection is done for doping of semiconductors. This process doesn’t generate electron-hole pairs.8. Which of the following is not correct about semiconductors in electronic devices? a) Electrons are present below Fermi level in a semiconductor b) Degenerated semiconductors behave like a conductor c) Fermi level is independent of temperature and doping d) Pentavalent atoms are used in an n-type extrinsic semiconductor View Answer Answer: c Explanation: Fermi level is the highest level of electrons at 0K. Below Fermi level, all levels are filled with electrons. Fermi level depends on the temperature and the doping of the semiconductor.9. Which of the following equation represents mass action law for semiconductors in electronic circuits? a) n × p = n i 2 b) n × p = n i c) n × p = n i 3 d) n × p = n i 1/2 View Answer Answer: a Explanation: Mass action law states that at a constant temperature, the product of the concentration of electrons and the concentration of holes is maintained constant in any type of semiconductor.10. Which of the following is correct about Hall Effect in electronic circuits? a) Hall voltage is very weak in metals as compared to semiconductors b) Hall voltage is directly proportional to the charge density c) Hall voltage is inversely proportional to the intensity of the magnetic field d) Intrinsic semiconductor has a positive temperature coefficient of hall constant View Answer Answer: a Explanation: Metals have an ocean of electrons. So, there is very little difference between positive and negative charges in metals. Thus, Hall voltage is very weak in metals as compared to semiconductors.11. Which of the following is not correct about a step-graded junction in electronic devices? a) Diodes with step-graded junctions are slower than a normal diode b) They are designed with abrupt junction c) They are either p + – n or p – n + junction d) Depletion layer penetrates more into the lightly doped region View Answer Answer: a Explanation: Step-graded junctions are designed with abrupt junctions. They are either p + – n or p – n + junction and diodes with step-graded junctions are faster than the normal diodes.12. Which of the following is correct about photo diode electronic devices? a) P-N junction is connected in reverse bias. b) Electron-hole pairs are generated by impurity injection in depletion layer c) It is a photovoltaic cell d) No external voltage is applied View Answer Answer: a Explanation: Photo diode is a photoconductive cell. External voltage is applied and P-N junction is connected in reverse bias. Electron-hole pairs are generated by photons in the depletion layer.13. Which of the following is wrong about solar cell electronic devices? a) Solar cell responsivity is directly proportional to the wavelength of light b) It produces dark current c) It is a photovoltaic cell d) No external voltage is applied View Answer Answer: b Explanation: Solar cell is a photovoltaic cell. No external voltage is applied and solar cell responsivity is directly proportional to the wavelength of the incident light. It doesn’t produce dark current.14. What type of semiconductor is used in LED electronic circuits? a) Intrinsic semiconductor b) Compound semiconductor c) Degenerated semiconductor d) Compensated semiconductor View Answer Answer: b Explanation: LEDs need compound type semiconductors because they have direct band gap. In direct band gap, photons are easily generated when electrons release energy during recombination.15. Which of the following semiconductor is mostly used to construct electronic circuits? a) Silicon b) Germanium c) Selenium d) Tin View Answer Answer: a Explanation: Silicon is mostly used to construct electronic circuits because silicon has a much higher PIV (Peak Inverse Voltage) than the other semiconductors. It is also very cheap.16. Which of the following is correct about NMOS electronic circuits? a) It has N-substrate b) For inversion positive voltage is applied to the gate terminal c) For accumulation positive voltage is applied to the gate terminal d) NMOS has holes as the majority of carriers View Answer Answer: b Explanation: NMOS has P-substrate and it has electrons as the majority carriers. For accumulation negative voltage is applied to the gate terminal and for inversion positive voltage is applied to the gate terminal.17. Which of the following is wrong about threshold voltage (V T ) in a MOSFET electronic circuit? a) If V T is less, channel form quickly for conductivity b) V T can be reduced by reducing oxide layer thickness c) V T is independent of ion implementation d) V T can be reduced by reducing substrate doping View Answer Answer: c Explanation: V T can be reduced by suitable ion implementation. Like in NMOS, positive donor ions are implemented to reduce repulsion to the electrons present in the channel.18. Which of the following is the correct relationship between trans-conductance (G m ) and drain to source current (I DS ) in an NMOS electronic circuit? a) G m ∝ I DS -3/2 b) G m ∝ I DS -1/2 c) G m ∝ I DS d) G m ∝ I DS 1/2 View Answer Answer: d Explanation: Trans-conductance in NMOS is defined as the change in the drain to source current with respect to the gate to source voltage. The correct relation is G m ∝ I DS 1/2,19. In which of the following region does BJT act as the amplifier electronic device? a) Cut-off b) Saturation c) Active d) Reverse saturation View Answer Answer: In the active region, the emitter-base junction is forward biased, the collector-base junction is reversed biased. This is the operating mode when amplification of signals occurs in BJT.20. Which type of semiconductor is used in Tunnel Diode? a) Compound semiconductor b) Elemental semiconductor c) Degenerated semiconductor d) Extrinsic semiconductor View Answer Answer: c Explanation: Degenerative N-type and degenerative p-type semiconductors are used in tunnel diodes. Tunnel diodes are used in microwave electronic devices and circuits.21. Which of the following is false about Fermi-Dirac distribution function f(E) used to understand semiconductors in electronic circuits? a) f(E) is the probability of finding an electron in an energy level E b) When the temperature decreases f(E) also increases c) f(E) doesn’t give the number of electrons in a given energy level d) f(E) doesn’t give the number of energy levels with electrons View Answer Answer: b Explanation: Fermi-Dirac distribution function f(E) is the probability of finding an electron in an energy level E. When temperature increases f(E) also increases.22. An electronic circuit wire of conductivity 5.8 × 10 7 mho-m is subjected to an electric field of 40 mV/m. What will be its current density? a) 2.32 × 10 6 A/m 2 b) 1.16 × 10 6 A/m 2 c) 4.64 × 10 6 A/m 2 d) 4.30 × 10 6 A/m 2 View Answer Answer: a Explanation: The current density (J) is the product of conductivity and electric field. The conductivity is 5.8 × 10 7 mho-m and the electric field is 40 mV/m. So, J = 5.8 × 10 7 × 40 × 10 -3 = 2.32 × 10 6 A/m 2,23. Mass action law is not valid for which type of semiconductors in electronic devices? a) Compound b) Elemental c) Degenerative d) Compensated View Answer Answer: c Explanation: Mass action law is related to the concentration of electrons and holes in a semiconductor. Degenerative type semiconductors show similar behavior to metal. So, Mass action law is not valid for them.24. Which of the following is the correct expression of current in an intrinsic semiconductor electronic circuit? a) I Total = I e + I h b) I Total = I e – I h c) I Total = I e + 2I h d) I Total = 2I e + I h View Answer Answer: a Explanation: When electric field is applied to an intrinsic semiconductor, electrons and holes move in the opposite direction. So, the total current will be the sum of the current due to electrons and holes.25. When an electronic circuit is in equilibrium then which of the following equation is valid? a) J drift + J diffusion = 1 b) J drift + J diffusion = 0 c) J drift + J diffusion = -1 d) J drift + J diffusion = 2 View Answer Answer: b Explanation: When an electronic circuit is in equilibrium then the net current density becomes 0. Current density occurs due to the drift and diffusion of ions. So, J drift + J diffusion = 0.26. Which of the following is wrong about P-N junction diodes used in electronic devices? a) They have three modes of operations b) They have dynamic resistance at low-frequency AC voltage c) They have diffusion capacitance at high-frequency AC voltage d) They can act as ON-OFF switches View Answer Answer: a Explanation: P-N junction diodes have two modes of operations i.e. forward and reverse bias. Forward bias is called ON switch and reverse bias is called OFF switch.27. What is the conductivity of an extrinsic type semiconductor electronic device at 0K? a) maximum b) zero c) can’t be determined d) minimum View Answer Answer: b Explanation: At T = 0K, conductivity will be zero because donar level ionization is zero, so no free electron is there in the conduction band. Conductivity is measured when free electrons are present in the conduction band for conduction.28. What is the conductivity of an extrinsic type semiconductor electronic device at 300K? a) Maximum b) Zero c) Can’t be determined d) Minimum View Answer Answer: a Explanation: At 300k, conductivity is maximum because of complete ionization of dopant levels which causes more free electrons conductivity in the conduction band.29. Which of the following effects is responsible for violating the mass action law in degenerative type semiconductor electronic devices? a) Thermal effect b) Bandgap narrowing effect c) Lattice vibration effect d) Electronic drift effect View Answer Answer: b Explanation: With a very high amount of doping in degenerative type semiconductors, atoms come closer. For this reason, the interatomic interaction cannot be neglected. So, the effective band gap becomes narrow.30. Which of the following diode is used in ultra-high speed switching electronic circuits? a) Zener diode b) Varactor diode c) Tunnel diode d) Schottky diode View Answer Answer: c Explanation: Due to tunneling, a large number of electrons penetrate through the junction, so a large amount of current is produced. And as we are considering a special diode, we can control its I-V characteristics to improve the switching speed.31. Which of the following diode is used in adjustable band pass filter electronic circuits? a) Zener diode b) Varactor diode c) Tunnel diode d) Schottky diode View Answer Answer: b Explanation: Band pass filter depends upon the value of the resistance and capacitance. In varactor diode, we can obtain capacitance by varying the input voltage. As capacitance becomes adjustable, it can be considered as an adjustable band pass filter.32. Forbidden Energy gap (E G ) of a semiconductor in electronic devices depends on which of the following factors? a) Interatomic distance b) Material constant c) Electron affinity d) Recombination and Generation View Answer Answer: a Explanation: Forbidden energy gap (E G ) of a semiconductor is directly proportional to the bond strength. And bond strength depends on the interatomic distance.33. Which of the following is the correct order of turn-off times? a) MOSFET < BJT < IGBT < SCR b) MOSFET < IGBT < BJT < SCR c) SCR < BJT < IGBT < MOSFET d) BJT < MOSFET < IGBT < SCR View Answer Answer: a Explanation: Electronic devices like MOSFET have the lowest turn-off times (nanoseconds). BJT has turn-off times in between nanoseconds to microseconds. IGBT and SCR have turn-off times of about 1 and 5 microseconds respectively.34. Which of the following is correct relation for saturation region in a NMOS electronic circuit? a) V DS >= V G + V T b) V DS >= V G – V T c) V DS <= V G – V T d) V DS >= V G ± V T View Answer Answer: b Explanation: For the saturation region, the drain to source voltage is greater than or equal to the difference between the gate voltage and the thermal voltage. So, V DS >= V G – V T,35. Which of the following type of transistor is preferred in digital and analog electronic circuits? a) BJT b) JFET c) MOSFET d) FET View Answer Answer: c Explanation: MOSFET is preferred in digital and analog electronic circuits because it is faster than all other transistors. Also, it has a very high input impedance.36. Which of the following is true about the depletion layer channel in an NMOS electronic circuit? a) Inverted change in the channel increases from source to drain b) Inverted charge remain constant c) Inverted change in the channel decreases from source to drain d) Potential in the channel decreases from source to drain View Answer Answer: c Explanation: When the depletion layer starts moving into the channel, due to the reverse bias of drain and substrate voltage, the inverted charge in the channel decreases from source to drain.37. Which of the following is true about Zener diode? a) It is lightly doped b) It is mostly used in voltage regulator electronic circuits c) It is used in forward bias d) It has avalanche breakdown View Answer Answer: b Explanation: Zener diode is a heavily doped diode. It is used in reverse bias. It has Zener breakdown. It is used in voltage regulators because it passes an excess amount of current in breakdown mode by maintaining constant voltage across the load.38. In which region does BJT act as the OFF switch in electronic circuits? a) Cut-off b) Saturation c) Active d) Reverse saturation View Answer Answer: b Explanation: In the saturation region, the emitter-base junction is forward biased, the collector-base junction is also forward biased. This is the operating mode when no current flows through BJT.

What is the semiconductor diode used as Mcq?

Physics Questions and Answers – Semiconductor Diode This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Semiconductor Diode”.1. Why is there a sudden increase in current in Zener diode? a) Due to the rupture of ionic bonds b) Due to rupture of covalent bonds c) Due to viscosity d) Due to potential difference View Answer Answer: b Explanation: The sudden increase in current in a Zener diode is due to the rupture of the many covalent bonds present.

• Therefore, the Zener diode should be connected in reverse bias.2.
• What is the semiconductor diode used as? a) Oscillator b) Amplifier c) Rectifier d) Modulator View Answer Answer: c Explanation: Semiconductor diode can be used as a rectifier.
• The function of a rectifier is that it converts an alternating current into direct current by allowing the current to pass through in one direction.3.

What is an oscillator? a) An amplifier with a large gain b) An amplifier with negative feedback c) An amplifier with positive feedback d) An amplifier with no feedback View Answer Answer: c Explanation: An oscillator is considered as an amplifier with positive feedback.

• It converts direct current from a power supply to an alternating current signal.
• It produces an alternating waveform without any input.4.
• What is rectification? a) Process of conversion of ac into dc b) Process of conversion of low ac into high ac c) Process of conversion of dc into ac d) Process of conversion of low dc into high dc View Answer Answer: a Explanation: Rectification is the process of conversion of alternating current into direct current.

The conversion first powers to alternating current then use a transformer to change the voltage, and finally rectifies power back to direct current.5. What is a Zener diode used as? a) Oscillator b) Regulator c) Rectifier d) Filter View Answer Answer: b Explanation: Zener diode can be used as a voltage regulator.

1. They can also be used as shunt regulators to regulate the voltage across small circuits.
2. Zener diodes are always operated in a reverse-biased condition.
3. Check this: | 6.
4. Forward biasing of p-n junction offers infinite resistance.
5. A) True b) False View Answer Answer: b Explanation: No, this is a false statement.

Forward biasing of p-n junction offers low resistance. In the case of an ideal p-n junction, the resistance offered is zero. So, forward biasing does not offer any resistance.7. When a junction diode is reverse biased, what causes current across the junction? a) Diffusion of charges b) Nature of material c) Drift of charges d) Both drift and diffusion of charges View Answer Answer: c Explanation: The reverse current is mainly due to the drift of charges.

It is due to the carriers like holes and free electrons passing through a square centimeter area that is perpendicular to the direction of flow.8. Identify the condition for a transistor to act as an amplifier. a) The emitter-base junction is forward biased and the base-collector junction is reverse biased b) No bias voltage is required c) Both junctions are forward biased d) Both junctions are reverse biased View Answer Answer: a Explanation: In order to use a transistor as an amplifier the emitter-base junction is set up as forward biased and the base-collector junction is set up as reverse biased.

This is the criteria for making a transistor function as an amplifier.9. What can a p-n junction diode be used as? a) Condenser b) Regulator c) Amplifier d) Rectifier View Answer Answer: d Explanation: A junction diode can be used as a rectifier. The rectifier converts alternating current into direct current.

1. During the positive half cycle, the diode is forward biased and allows electric current through it.10.
2. What is a transistor made up of? a) Chip b) Insulator c) Semiconductor d) Metal View Answer Answer: c Explanation: A transistor is a semiconductor device.
3. Transistors can work either as an amplifier or as a switch.

It is used to amplify or switch electronic signals. A transistor is a solid-state device made up of silicon and germanium. Sanfoundry Global Education & Learning Series – Physics – Class 12, To practice all areas of Physics,, Next Steps:

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Are LEDs made of semiconductors?

A light-emitting diode (LED) is a semiconductor device that emits light when a forward voltage is applied to it. The fact that certain semiconductors emit light has been observed by a number of semiconductor researchers from early on. After it was successfully demonstrated in 1960 that ruby could be used as a source of laser, inspired researchers sought to produce laser beams using the electroluminescence effect of semiconductors.

At the time, compound semiconductors based on gallium arsenide (GaAs) and other materials were attracting greater attention than silicon-based semiconductors. Since GaAs is superior to silicon in terms of electric properties at high frequencies, it was considered to be suitable for laser applications, too.

After a fierce competition among researchers, three American teams separately conducted successful experiments on LEDs in 1962.

Which of the following materials can be used to produce infrared LED Mcq?

Gallium Arsenide is used for making infrared LED. Hence, option 2 is correct.