Question

How does the energy gap of an intrinsic semiconductor effectively change when doped with a (a) trivalent impurity, and (b) pentavalent impurity ? Justify your answer in each case.

Assertion (A) : In a semiconductor, the electrons in the conduction band have lesser energy than those in the valence band. Reason (R) : Donor energy level is just above the valence band in a semiconductor.

Suppose a pure Si crystal has 5 × 10²⁸ atoms m⁻³. It is doped by 1 ppm concentration of boron. Calculate the concentration of holes and electrons, given that nᵢ = 1·5 × 10¹⁶ m⁻³. Is the doped crystal n-type or p-type ?

Draw the circuit diagrams for obtaining the V – I characteristics of a p-n junction diode. Explain briefly the salient features of the V – I characteristics in (i) forward biasing, and (ii) reverse biasing.