Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 05

Years: MAY 2012

1. It is formed when a layer of material with particular band gap energy is sandwiched with a layer of material having higher band gap energy. This is called double hetrojunction because there are two hetrojunction placed on each side of the active material.

2. The device shown consists of a P-type GaAs layer sandwiched between a P-type AlGaAs and n-type AlGaAs Layer.

3. When a forward bias is applied electrons from the n-type layer are injected through the p-n junction into the p-type GaAs Layer where they become minority carriers.

4. These minority carriers diffuse away from the junction, recombining with majority carriers as they do.

1. Photons are therefore produced with energy corresponding to the bandgap energy of the p-type GaAs layer.

2. The injected electrons are inhibited from diffusing into the p-type AlGaAs layer because of the potential barrier presented by the p-p hetrojunction.

3. Therefore the DH structure provides the most efficient incoherent sources for application.

Limitations of Double hetrojunction LED:

1. It comes from the very small potential barrier that an electron, in the conduction band, encounters when it reaches the p-side of the junction.

2. They are only usable at low temperatures.