Question

Distinguish between an intrinsic and extrinsic semiconductor.

Answer 1

Hint: As a very first step, one could read the question well and hence note down the important points from it. Then recall what are intrinsic and extrinsic semiconductors and you could begin from the definition of the two terms. You could also distinguish between the two in other aspects. Also, give examples to both.

Complete step-by-step solution:
In the question, we are asked to distinguish between an intrinsic and extrinsic semiconductor and also draw their respective energy band diagrams.
(a) The semiconductors in which the addition of impurity into a pure semiconductor takes place is called an intrinsic semiconductor, whereas, extrinsic semiconductors are the ones where doping of impurity into a pure semiconductor takes place.
(b) In intrinsic semiconductors the number density of electrons and holes are the same, i.e., holes present in the valence bond are equal to the free electrons in the conduction band. Whereas, in extrinsic semiconductors, an unequal number of electrons and holes are present. Holes are present in excess in p-type semiconductors and electrons are present in excess in n-type semiconductors.
(c) Electric conductivity in intrinsic semiconductors is low when compared to extrinsic semiconductors.
(d) Electric conductivity in intrinsic semiconductors is a function of temperature and in addition to temperature the amount of impurity doped also affects the electrical conductivity in extrinsic semiconductors.

Note: Examples for intrinsic semiconductors are pure form of silicon and germanium and examples for extrinsic semiconductors are dopants like arsenic, antimony, phosphorus, aluminium, indium, etc added to pure form of silicon and aluminium. There are mainly two types of impurities: pentavalent impurity and trivalent impurity.