Question:

(a) (i) Describe the difference between intrinsic and extrinsic semiconductors.

(ii)Is it possible for compound semiconductors to exhibit intrinsic behaviour? Describe your answer.

(iii) Brie?y describe electron and hole motions in a p-n junction for forward and reverse biases; then explain how these lead to recti?cation.

(iv) How would you expect increasing temperature to in?uence the operation of p-n junction recti?ers and transistors? Describe.

(b) The room temperature electrical conductivity of intrinsic silicon is 4 x 10^-4 (Ωm)^-1. An extrinsic n-type silicon material is desired having a room-temperature conductivity of 150 (Ωm)^-1.

(i) Specify from the periodic table on page 9, a donor impurity type that will render Silicon n-type.

(ii) Evaluate the number of free electrons per unit volume of Silicon. Assume that the electron and hole mobilities are the same as for the intrinsic material (0.14 m²/V-s) and that at room temperature the impurities are exhausted.

(iii) Calculate the number of Si atoms per cubic meter, Nsi.

(iv) Calculate the concentration of donor impurities in atom percent (Cd) to yield these electrical characteristics.

(atomic weight of Si=28.09 g/mol, Avogadro's number NA= 6.023x10²³ atoms/mol, electronic charge ?e?= 1.6x10^-19C )