To obtain electrons as majority charge carriers in a semiconductor, the impurity mixed is 
(1) Monovalent         

(2) Divalent

(3) Trivalent               

(4) Pentavalent

 In a P-type semiconductor, germanium is doped with

(1) Boron                     

(2) Gallium

(3) Aluminium             

(4) All of these

In a P-type semiconductor

(1) Current is mainly carried by holes

(2) Current is mainly carried by electrons

(3) The material is always positively charged

(4) Doping is done by pentavalent material

If ${\mathrm{n}}_{\mathrm{e}}$ and ${\mathrm{n}}_{\mathrm{h}}$ are the number of electrons and holes in a semiconductor heavily doped with phosphorus, then

(1) ${\mathrm{n}}_{\mathrm{e}}$>> ${\mathrm{n}}_{\mathrm{h}}$               

(2)  ${\mathrm{n}}_{\mathrm{e}}$<< ${\mathrm{n}}_{\mathrm{h}}$  

(3) ${\mathrm{n}}_{\mathrm{e}}$$\le$${\mathrm{n}}_{\mathrm{h}}$                 

(4) ${\mathrm{n}}_{\mathrm{e}}$ = ${\mathrm{n}}_{\mathrm{h}}$  

GaAs is 

(1) Element semiconductor

(2) Alloy semiconductor

(3) Bad conductor

(4) Metallic semiconductor

For germanium crystal, the forbidden energy gap in joules is

(1) $1.12\times {10}^{-19}$        

(2) $1.76\times {10}^{-19}$

(3)  $1.6\times {10}^{-19}$         

(4) Zero

At ordinary temperatures, the electrical conductivity of semi conductors in  mho/meter is in the range 
(1)${10}^{-3}$ to ${10}^{-4}$            

(2)${10}^6$ to ${10}^9$

(3) ${10}^{-6}$ to  ${10}^{-10}$         

(4) ${10}^{-10}$ to ${10}^{-16}$

Energy bands in solids are a consequence of

1. Ohm’s Law

2. Pauli’s exclusion principle

3. Bohr’s theory

4. Heisenberg’s uncertainty principle

A pure semiconductor behaves slightly as a conductor at

(1) Room temperature             

(2) Low temperature

(3) High temperature               

(4) Both (b) and (c)