Intrinsic and Extrinsic Semiconductors p type n type - UNSOLVED PRACTICE SET

Q7. What is an intrinsic semiconductor? Why is its conductivity very low at room temperature?

Q8. Distinguish between p-type and n-type semiconductors in terms of:

(a) Type of dopant added

(b) Majority charge carriers

(c) Position of Fermi level

Q9. Why does the conductivity of an extrinsic semiconductor depend on temperature differently in different temperature ranges?

Q10. Explain why a p-type semiconductor is electrically neutral overall, even though it has excess holes.

Q11. What happens to the Fermi level when a semiconductor is doped with:

(a) A pentavalent impurity?

(b) A trivalent impurity?

Q12. Why is germanium preferred over silicon for some high-frequency applications, despite silicon being cheaper and more abundant?

Q13. Explain the process of doping in semiconductors. Describe how n-type and p-type semiconductors are produced and discuss the energy band diagrams for both.

Q14. Derive the expression for the intrinsic carrier concentration in a semiconductor. Explain how doping increases the conductivity of a semiconductor by many orders of magnitude.

Q15. Discuss the variation of Fermi level with temperature in intrinsic and extrinsic semiconductors. Draw diagrams showing the position of the Fermi level in n-type and p-type semiconductors at different temperatures.

Q16. The intrinsic carrier concentration of silicon at 300 K is 1.5 × 10¹⁶ m⁻³. The silicon sample is doped with phosphorus to a concentration of 10²² m⁻³.

(a) Calculate the electron concentration in the doped semiconductor at 300 K.

(b) Calculate the hole concentration using the mass action law (n × p = n_i²).

(c) Calculate the ratio of electron concentration to hole concentration.

(d) Identify whether the semiconductor is n-type or p-type.

Q17. A silicon sample is doped with boron at a concentration of 5 × 10²¹ m⁻³. The intrinsic carrier concentration at 300 K is 1.5 × 10¹⁶ m⁻³.

(a) Calculate the hole concentration in the doped semiconductor.

(b) Calculate the electron concentration.

(c) If the mobility of holes is 0.05 m²/V·s and that of electrons is 0.13 m²/V·s, calculate the conductivity of the sample.

(d) Compare this conductivity with the intrinsic conductivity of silicon.

Q18. In your school electronics club, students are learning about semiconductor fabrication.

(a) A student has a pure silicon wafer. At room temperature, it has an intrinsic carrier concentration of 1.5 × 10¹⁰ cm⁻³. Calculate the total number of charge carriers in a 1 cm³ sample.

(b) The student then diffuses phosphorus (a pentavalent atom) into the silicon at a concentration of 10¹⁶ cm⁻³. Calculate the new electron and hole concentrations at room temperature.

(c) The student measures the resistivity of the doped sample as 0.5 Ω·cm. Calculate the conductivity and verify it using the carrier concentrations and mobilities (μ_n = 1350 cm²/V·s).

(d) A classmate suggests that adding more dopant always increases conductivity. Discuss whether this is true and what happens at very high doping concentrations (degenerate semiconductors).

(e) In India, semiconductor manufacturing is growing under the 'India Semiconductor Mission.' Explain why controlling the doping concentration precisely (to within parts per billion) is crucial for making reliable transistors and chips.