Drift Current and Diffusion Current :

There are two mechanisms in which electrons and holes move through a semiconductor. One of these is termed as drift and other is diffusion. When the movement of charge carries is under the influence of an applied electric field, the resultant current is termed as drift current. A second type of current, called the diffusion current, also exists in a semiconductor. The diffusion of charge carriers is as a result of a gradient of carrier concentration. In this case concentrations of charge carriers tend to distribute themselves uniformly throughout the semiconductor crystal. This movement continues until all the carries are evenly distribute themselves uniformly throughout the semiconductor crystal. This movement continues until all the carriers are evenly distributed throughout the material. The type of movement of charge carriers is called the diffusion current. Both drift and diffusion occur simultaneously in a semiconductor device.