Drift Current

Drift Current

• When a voltage is applied to a semiconductor, the free electrons try to move in a straight line towards the positive terminal of the battery. The electrons, moving towards positive terminal collide with the atoms of semiconductor and connecting wires, along its way. Each time the electron strikes an atom, it rebounds in a random direction. But still the applied voltage make the electrons drift towards the positive terminal. This drift causes current to flow in a semiconductor, under the influence of the applied voltage. This current produced due to drifting of free electrons is called drift current and the velocity with which electrons drift is called drift velocity. Thus drift current means the flow of current due to bouncing of electrons from one atom to another, travelling from negative terminal to positive terminal of the applied voltage.

Key Point : The direction of conventional current is always opposite to the direction of drifting electrons.

• This is shown in the Fig. 1.2.1.

• The conventional current direction is always from positive terminal to the negative terminal of the battery. But the operating principle of many semiconductor devices is generally explained considering the direction of flow of electrons rather than the conventional current.

Review Question

1. What is drift current ?