Question

True or False Then provide a brief justification for your answer .

1 Indirect semiconductors are best suited for optoelectronic applications (LED, lasers). True or False and Reason :

2 Silicon has four electrons in the outer shell . True or False and Reason :

3 There is strong electric field in the neutral region of a p-n diode . True or False and Reason :

4 Conductivity of n-doped semiconductors decreases at very low temperatures due to low impurity scattering.. True or False and Reason :

5 Diffusion current dominates current flow in ideal pn diode.. True or False and Reason :

6 Efficient LED use semiconductor materials with short electron life-time.. True or False and Reason :

7 At temperature T=0 K, number of free electrons in semiconductor is zero. . True or False and Reason :

8 The junction capacitance in pn diode increases as the doping levels of P and N regions are increased.. True or False and Reason :

9 Zener diodes have highly doped N- and P-regions.. True or False and Reason :

10 A solar module efficiency is lower than the efficiency of individual solar cells in the module. True or False and Reason :

11 Breakdown in reverse biased Zener diode is due to avalanche multiplication. True or False and Reason :

12 Absorption of photons with energy less than energy gap in solar cells leads to more efficient solar cells. True or False and Reason :

13 An LED emits light when electrons and holes recombine. True or False and Reason :

14 A photon with energy less than energy gap of a semiconductor is transmitted through the semiconductor. True or False and Reason :

Answer 1

1. False. Reason: They have small absorption coefficient.
2. True. Reason: The atomic number of silicon is 14. So the first two electrons occupy first shell, the next eight occupy second shell and the remaining four are in the outer shell which form valence electrons.
3. True. Reason: The neutral region called depletion region is devoid of any moving charges but has majority charge carriers (holes and electrons) on either side. So this gives rise to strong electric field.
4. False. Reason: Impurity scattering increases with decreasing temperature and mobility of electrons decreases . So reduced conductivity at low temperatures is not due to reduced impurity scattering but due to reduced mobility.