SOLUTION

• The materials which have resistivities lying between those of an insulator and a conductor are known as semiconductors.
• At absolute zero. pure and perfect crystals of the semiconductors are non-conducting, their resistivity approaching the resistivity of an insulator.
• They can be made conducting by adding impurities, and due to thermal, agitation, lattice defects, etc.
• The resistivity of a semiconductor depends upon the temperature and it decreases with the rising temperature; consequently, a semiconductor crystal becomes conducting even at room temperature.
• At room temperature, their resistivity lies in the range 10² to 10⁹ ohm-cm and is thus intermediate between the resistivity of a good conductor (10^-6 ohm-cm) and an insulator (10¹⁴ to 10²² ohm-cm).
• At very low temperatures a semiconductor behaves as an insulator.