About Semiconductors & Types

A semiconductor material has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Semiconductors are the foundation of modern electronics. Semiconducting materials exist in two types - elemental materials and compound materials.
      Generally we have different types of semiconductors based on properties in that
                         1. intrinsic semiconductor
                         2. Extrinsic semiconductor

Intrinsic semiconductors :
             An intrinsic semiconductor material is also called as undoped semiconductor or i-type semiconductor, is chemically very pure and possesses poor conductivity. It has equal numbers of negative carriers (electrons) and positive carriers (holes). A silicon crystal is different from an insulator because at any temperature above absolute zero temperature, there is a finite probability that an electron in the lattice will be knocked loose from its position, leaving behind an electron deficiency called a "hole".
                 by we applying external energy (voltage,temperature) both the electrons and the holes can contribute small current flow.

In Single Word : pure semiconductor

Extrinsic Semiconductor :

             Where as an extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping, which alters the electrical properties of the semiconductor and improves its conductivity. Introducing impurities into the semiconductor materials (doping process) can control their conductivity.