Some Basic Definitions related to P-N junction diode

Some basic definition :

Drift Current: The steady flow of electrons caused by the applied electric field constitutes the drift current. Because of the applied electric field electrons gain energy and move towards the positive terminal. They have many collisions, because of which they get accelerated and gain certain component of velocity.

Diffusion Current: the diffusion of charge carriers as a result of difference in the carrier concentration from one region to another constitutes the current called as diffusion current. This movement continues till all the carriers are evenly distributed throughout the material.

Breakdown Voltage: under normal reverse voltage , a very small reverse current flows through the P-N junction. However when this voltage is increased there comes a stage at which the junction breaks down with the sudden rise in current. This voltage is called breakdown voltage.

Knee Voltage: The forward voltage at which the current starts increasing rapidly is called as knee voltage. It is also known as cut-in voltage. Its value for silicon is 0.7 and that for germanium is 0.3.

Maximum forward current: It’s the highest instantaneous forward current that a P-N junction can conduct without damage to the junction.

Peak Inverse Voltage: Maximum reverse voltage that can be applied to the junction without it getting damage.

Diode current Equation:

ID=I0(e VD/ηVT -1),

Where,

ID = diode current (positive for FB and negative for RB flowing from p to n side)

I0 = Reverse saturation current

VD = Applied diode voltage (positive for FB and Negative for reverse bias)

VT = volt equivalent of temperature= T/11600,

At room temperature its value is 26 mV.

The factor η is considered to neglect the effect of carrier generation and recombination in the depletion region. Still it is considered for silicon.

Thus η=2 for silicon and η= 1 for germanium.