Question

what is isoelectronic impurity and its role in laser device?

Do optical devices are fabricated with only direct band gap? why

what is double hetro junction laser? draw band diagram

what is the role of reflective index in laser device material ? explain with graphs?

Answer 1

1.An isoelectronic impurity is one having the same outer electron configuration as the atom of the host crystal which it replaces. Examples are germanium in silicon, or arsenic in gallium phosphide.

It's role in laser devices is technique for increasing the efficiencyis to introduceisoelectronic impurities such as Ntoms and devices based on this laser devices

2.

It can be explained based on the energy and momentum conservation required in the electron-photon interaction. The direct bandgap semiconductor, which has a vertically aligned conduction and valence band, (a). Absorption of a photon is obtained if an empty state in the conduction band is available for which the energy and momentum equals that of an electron in the valence band plus that of the incident photon. Photons have little momentum relative of their energy since they travel at the speed of light. The electron therefore makes an almost vertical transition on the E-k diagram.

For an indirect bandgap semiconductor, the conduction band is not vertically aligned to the valence band (b). Therefore a simply interaction of an incident photon with an electron in the valence band will not provide the correct energy and momentum corresponding to that of an empty state in the conduction band. As a result absorption of light requires the help of another particle, namely a photon 3.A double heterostructure is formed when two semiconductor materials are grown into a "sandwich". One material is used for the outer layers, and another of smaller band gap is used for the inner layer. In this example, there are two AlGaAs-GaAs junctions, one at each side of the inner layer. 4.