Define the following terms with reference to semiconductors devices.(i) Intrinsic semiconductor(ii) Extrinsic semiconductors(iii) Diffusion current(iv) Drift current

(i) Intrinsic Semiconductor: An intrinsic semiconductor is a pure semiconductor without any significant dopant species present. The number of charge carriers is therefore determined by the properties of the material itself instead of the amount of impurities. In intrinsic semiconductors, the number of excited electrons and the number of holes are equal: n = p. Silicon and germanium are examples of intrinsic semiconductors.

(ii) Extrinsic Semiconductors: Extrinsic semiconductors are doped semiconductors. Doping is the process of adding impurity to the semiconductor to increase the number of free charge carriers. When the doping material is added, it takes away electrons from the semiconductor or it provides extra holes. Depending on the type of impurity added, extrinsic semiconductors can be classified as n-type (negative type) or p-type (positive type).

(iii) Diffusion Current: Diffusion current in a semiconductor is the current due to the movement of charge carriers from a region of higher concentration to a region of lower concentration. This is caused by the concentration gradient. In a semiconductor, the diffusion current is due to the movement of holes and electrons.

(iv) Drift Current: Drift current is the electric current, or movement of charge carriers, which is due to the applied electric field. When an electric field is applied, the electrons and holes move, constituting a current. The direction of the current is opposite to the direction of the electron's motion. The drift current is directly proportional to the electric field.