Energy Band Theory, Intrinsic And Extrinsic SemiConductor (Board Level)

1.

A semiconductor has the electron concentration 0.45 × 10¹² m^–3 and hole concentration 5 × 10²⁰ m^–3. Find its conductivity. Given: electron mobility = 0.135 m²V^–1s^–1 and hole mobility = 0.048 m²v^–1s^–1; e = 1.6 × 10^–19 coulomb.

(a) 1.548 \displaystyle \Omega m^–1

(b) 1.224 \displaystyle \Omega m^–1

(c) 3.845 \displaystyle \Omega m^–1

(d) 0.456 \displaystyle \Omega m^–1

Ans (c)

2.

When the voltage drop across a p–n junction diode is increased from 0.70V to 0.71 V, the change in the diode current is 10 mA. What is the dynamic resistance of the hole?

(a) 27 \displaystyle \Omega

(b) 20 \displaystyle \Omega

(c) 4 \displaystyle \Omega

(d) 1 \displaystyle \Omega

Ans (d)

3.

In a p type semiconductor the acceptor level is situated 57 meV above the valence band. The maximum wavelength of light required to produce a hole will be

(a) 57 × 10^–3Å                                

(b) 11.61 × 10^–33 watt                 

(c) 57 Å    

(d) 217100 Å.

Ans  (d)

4.

The band of maximum energy in which electrons are present is called

(a) valence band                         

(b) forbidden band                    

(c) conduction band                   

(d) fermi band.

Ans  (a)

5.

The relation between the number of free electrons in semiconductors (n) and its temperature (T) is

(a) n \displaystyle \propto T                           

(b) n\propto \sqrt{T}                                        

(c) n \displaystyle \propto T^3/2                       

(d) n \displaystyle \propto T².

Ans  (c)

6.

The electron mobility in an n type germanium is 3900 cm²/V-s and its conductivity is 6.24 mho cm^–1, then the impurity concentration will be

(a) 10¹⁶/cm³                         

(b) 10¹⁵/cm³                                  

(c) 10¹³/cm                           

(d) 10¹²/cm³.

Ans (a)

7.

Polymers are the substance which are

(a) amorphous in nature                  

(b) semi-solids

(c) crystalline in nature                                                

(d) none of these.

Ans (d)

8.

In which case is the junction diode forward biased