Match items in List-I with items in List-II most suitable.

List-I	List-II
a. LED	1. Heavy doping
b. Avalanche Photodiode	2. Coherent radiation
c. Tunnel diode	3. Spontaneous emission
d. LASER	4. Current gain

A. Metals B. Semiconductors C. Insulators D. All of the above

A. Drift of holes B. Diffusion of holes C. Drift of electrons D. Diffusion of electrons

A. Both A and R are true and R is correct explanation of A B. Both A and R are true but R is not a correct explanation of A C. A is true but R is false D. A is false but R is true

A. Forward bias voltage B. Potential barrier C. Rate of thermal generation of electron hole pairs D. None of the above