Applications of semiconductor

LIGHT-EMITTING DIODE

• LED is specially prepared pn junction diode which operated in forward bias.

• Under forward bias conditions, it can emit radiation by electro luminescence in the UV,visible or infrared regions of the electromagnetic spectrum (beacause of recombination of electrons and holes)

• The quanta of light energy released is approximately proportional to the band gap of the semiconductor (energy gap > 1.8 eV.)

• The IV characteristics of an LED is dependent on the color that is chosen some of them are shown in the below table

Document

Color	Wavelength [nm]	Voltage drop [ΔV]	Semiconductor material
Infrared	λ > 760	ΔV < 1.63	Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)
Red	610 < λ < 760	1.63 < ΔV < 2.03	Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Orange	590 < λ < 610	2.03 < ΔV < 2.10	Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Yellow	570 < λ < 590	2.10 < ΔV < 2.18	Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Green	500 < λ < 570	1.9^[70] < ΔV < 4.0	Traditional green: Gallium(III) phosphide (GaP) Aluminium gallium indium phosphide (AlGaInP) Aluminium gallium phosphide (AlGaP) Pure green: Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN)
Blue	450 < λ < 500	2.48 < ΔV < 3.7	Zinc selenide (ZnSe) Indium gallium nitride (InGaN) Silicon carbide (SiC) as substrate Silicon
Violet	400 < λ < 450	2.76 < ΔV < 4.0	Indium gallium nitride (InGaN)
Purple	Multiple types	2.48 < ΔV < 3.7	Dual blue/red LEDs, blue with red phosphor, or white with purple plastic
Ultraviolet	λ < 400	3.1 < ΔV < 4.4	Diamond (235 nm)^[71] Boron nitride (215 nm) ^[72]^[73] Aluminium nitride (AlN) (210 nm)^[74] Aluminium gallium nitride (AlGaN) Aluminium gallium indium nitride (AlGaInN)—down to 210 nm ^[75]
Pink	Multiple types	ΔV ~ 3.3^[76]	Blue with one or two phosphor layers: yellow with red, orange or pink phosphor added afterwards, or white phosphors with pink pigment or dye over top.^[77]
White	Broad spectrum	ΔV = 3.5	Blue/UV diode with yellow phosphor

• LED Activation chart for different colours

	Voltage	Amperes
Red	1.882	0.0021
Green	1.89	0.0021
Yellow	1.819	0.0021
Blue	2.64	0.0021

Applications of LED

1. LED used in burglar alarms.

2. Seven-segment display of LED used as an Indicator

3. LED used in ON-OFF switch.

Advantages of LED’s

1. Very low voltage and current are enough to drive the LED. (Voltage range- 1 to 2 volts.)

2. The response time is very less- only about 10 nanoseconds.

3. The device does not need any heating and warm up time.

4. Miniature in size and hence light weight.

5. An LED has a life span of more than 20 years.

Disadvantages of LED’s

1. A slight excess in voltage or current can damage the device.

2. The device is known to have a much wider bandwidth compared to the laser.