Extrinsic Semiconductor

Extrinsic Semiconductor

• As pure intrinsic semiconductor has poor conductivity some impurity is added to it to increase the conductivity such impurity is purposely added to make the material suitable for manufacturing of the semiconductor devices. Such impure semiconductor is called an extrinsic semiconductor.

Doping and Dopants

• The process of adding other material to an intrinsic semiconductor, to improve its conductivity is called doping.

• The impurity added is called dopant and the resulting doped semiconductor material is called extrinsic semiconductor.

• There are two types of impurities used to obtain two different types of extrinsic semiconductors called p type and n type.

• The impurity having five valence electrons is called pentavalent impurity. When this is added, its each atom donates one free electron and such doping is called donor doping. The examples of pentavalent impurity are arsenic, bismuth, phosphorous etc. This creates n‒type extrinsic semiconductor.

• The impurity which has three valence electrons is called trivalent impurity. When this is added, its each atom creates one hole which is ready to accept an electron. Hence this is called acceptor doping. The examples of trivalent impurity are gallium, indium and boron. This creates p‒type extrinsic semiconductor.

Review Questions

1. Define an extrinsic semiconductor.

2. What is doping? Explain trivalent and pentavalent dopants with suitable examples.