Semiconductor: Important Part B Questions

Electron Devices

Chapter 1: Semiconductor

Important Part B Questions 

1. Explain the classification of materials based on energy band diagram.

2. Explain the concept of hole current.

3. Explain intrinsic semiconductor.

4. Explain generation of electron‒hole pairs in an intrinsic semiconductor.

5. Explain how conduction takes place in an intrinsic semiconductor.

6. Describe the generation and recombination of charge carriers in intrinsic semiconductors.

7. Define mobility of a charged particle and state its units.

8. Derive the general expression for drift current density and conductivity of a material.

9. The resistance per unit length of a piece of copper wire with circular cross section with diameter of 1.03 mm is 2.5×10^‒4Ω/cm. Concentration of free electrons is 8.4×10²⁸ per m³. The current density is 2.1× 10⁶ A/m². Calculate current flowing, conductivity, velocity of free electrons and mobility.

[Ans. : 1.749 mA, 4.8×10⁷(Ω‒m)^‒1, 1.56×10^-4 m/s, 3.567 × 10^‒3 m² N‒sec]

10. Obtain the expression for conductivity of semiconductor.

11. What is intrinsic concentration? Obtain the expression of conductivity of intrinsic semiconductor.

12. A bar of intrinsic Silicon has a cross‒sectional area of 2.5 × 10^-4 m². The electron density is 1.5 × 10¹⁶ per m³. How long the bar be in order that current in the bar will be 1.2 mA when 9 volts are applied across it? Assume: μ_n = 0.14 m²/V‒sec, μ_p = 0.05 m²/V‒sec.

[Answer: 0.856 mm]

13. Define an extrinsic semiconductor.

14. What is doping? Explain trivalent and pentavalent dopants with suitable examples.

15. Explain the formation of n‒type material and conduction in n‒type material.

16. Explain the following:

i) Formation of p‒type semiconductor.

ii) Conduction in p‒type material.

17. Draw a diagram to illustrate drift current and diffusion current in a semiconductor material. Briefly explain.

18. Obtain the expression for drift current density and conductivity of a semiconductor.

19. Obtain the expressions for conductivity of n‒type and p‒type materials.

20. Consider silicon at room temperature of 27 °C. Assuming μ_n = 1350 cm³/V‒s and μ_P=0.048m²/V‒s, find conductivity if silicon is doped with

a) N_D = 5×10¹⁶/cm³,

b) N_A=5×10¹⁶/cm³

[Ans.: 10.8 (Ω‒cm)^‒1, 3.84 (Ω‒cm)^‒1]

21. State and explain the law of mass action.

22. Explain the carrier concentrations in extrinsic semiconductors.

23. Explain the equation of charge neutrality.

24. What is diffusion current? Derive the expressions for the diffusion current densities.

25. Explain Einstein's relationship and voltage equivalent of temperature.

26. Define mean life time and diffusion length for the charge carriers.

27. State and explain the continuity equation.

28. Derive the expression for the potential difference existing in a continuously graded semiconductor.

29. Explain the law of junction. Hence prove the law of mass action from it.