Fermi Level in Semiconductor Materials

The Fermi level in a semiconductor is the probability that energy levels in a valence band and conduction band in the atoms are occupied. At absolute zero temperature, a semiconductor acts as a perfect insulator. As the temperature increases, free electrons are made available.  An intrinsic semiconductor is a pure crystal with no impurities or defect atoms. In an intrinsic semiconductor, the probability of occupation of energy levels in either the conduction band or the valence band are equal. The Fermi level of an intrinsic semiconductor lies between the valence band and the conduction band. This area between both bands is known as the forbidden band.

fermi

Where KB is the Boltzmann constant (1.3806503 × 10-23 m2 kg s-2 K-1), T is the absolute temperature of the intrinsic semiconductor, Nv is the density of states in the valence band, the hole concentration in the valence band is:

hole

Where Nc is the density of states in the conduction band, the electron concentration in the conduction band is calculated:

electron

The Fermi level for an intrinsic semiconductor is given as the average of the conduction band level and the valence band level.

fermilev

 

Electron Doping

A intrinsic semiconductor may be altered by adding controlled amounts of specific atoms, called dopants to the crystal. This alters the number of electrons in the conduction bands or electron holes in the valence bands.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s