Question

LASER action is found in _________ semiconductor.

• A. direct bond gap
• B. indirect bond gap
• C. germanium
• D. silicon

Answer 1

The correct option is A direct bond gap

Direct band gap: If the crystal momentum of electrons and holes is the same in both conduction band and valence band an electron can directly emit by photon.

Indirect band gap: a photon cannot be emitted because the electron must pass through intermediate state and transfer momentum to crystallice. Whereas in germanium, silicon which are intrinsic semiconductor, no electron – hole recombination take place so no laser action can be achieved