Research Paper on Diode

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Light Emitting Diodes (LEDs)

ELE 432 Assignment # 3 Vijay Kumar Peddinti

Light Emitting Diodes Principle Synopsis: To explain the theory and the underlying principle behind the functioning of an LED Brief History: • The first known report of a light-emitting solid-state diode was made in 1907 by the British experimenter H. J. Round.

(material.eng.usm.my/stafhome/zainovia/EBB424e/LED1.ppt)

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In the mid 1920s, Russian Oleg Vladimirovich Losev independently created the first LED, although his research was ignored at that time. In 1955, Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys. Experimenters at Texas Instruments, Bob Biard and
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In these materials, additional dopants(impurities) are added which form very shallow donor states. These donor states capture the free electrons locally; provides the necessary momentum shift for recombination. These donor states serve as the recombination centers. This is called Indirect (non-radiative) Recombination. Figure3 shows the E-k plot of an indirect band gap material and an example of how Nitrogen serves as a recombination center in GaAsP. In this case it creates a donor state, when SiC is doped with Al, it recombination takes place through an acceptor level.

The indirect recombination should satisfy both conservation energy, and momentum. Thus besides a photon emission, phonon(See Appendix 3) emission or absorption has to take place. GaP is an example of an indirect band-gap material.

Figure 3: Indirect Bandgap and NonRadiative recombination

The wavelength of the light emitted, and hence the color, depends on the band gap energy of the materials forming the p-n junction. The emitted photon energy is approximately equal to the band gap energy of the semiconductor. The following equation relates the wavelength and the energy band gap. hν = Eg hc/λ = Eg λ = hc/ Eg Where h is Plank’s constant, c is the speed of the light and Eg is the energy band gap Thus, a semiconductor with a 2 eV band-gap emits light at about 620 nm, in the red. A 3 eV band-gap material would emit at 414 nm, in the violet.
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