An?intrinsic semiconductor?is an undoped semiconductor. This means that holes in the valence band are vacancies created by electrons that have been thermally excited to the conduction band, as opposed to doped?semiconductors?where holes or electrons are supplied by a ?foreign? atom acting as an impurity.

Doping?is the process of adding impurities to intrinsic semiconductors?to alter their properties. Normally Trivalent and Pentavalent elements are used to dope Silicon and Germanium. When a intrinsic semiconductor?is?doped?with Trivalent impurity it becomes a P-Type?semiconductor.

Motion of hole is a convenient way of describing the actual motion of bound electrons

This?current?is called the diffusion?current. The drift?current?and the diffusion current?make up the?total current?in the conductor. The change in the concentration of the carrier particles develops a gradient. Due to this gradient, an electric field is produced in the?semiconductor.