PN Junction Diode and its Characteristics
P-N junction diode is the most fundamental and the simplest electronics device. When one side of an intrinsic semiconductor is doped with acceptor i.e, one side is made p-type by doping with n-type material, a p-n junction diode is formed. This is a two terminal device. It appeared in 1950’s.
P-N junction can be step graded or linearly graded. In step graded the concentration of dopants both, in n-side and in p-side are constant up to the junction. But in linearly graded junction, the doping concentration varies almost linearly with the distance from the junction. When the P-N diode is in unbiased condition that is no voltage is applied across it, electrons will defuse through the junction to p-side and holes will defuse through the junction to n-side and they combine with each other.
Thus the acceptor atom near the p-side and donor atom near n-side are left unutilized. An electron field is generated by these uncovered charges. This opposes further diffusion of carriers. So, no movement of region is known as space charge or depletion region.
P-N Junction Diode CharacteristicsLet's a voltage V is applied across a p-n junction and total current I, flows through the junction. It is given as. Here, IS = reverse saturation current e = charge of electron ɳ = emission co-efficient KB = Boltzmann constant T = temperature
The current voltage characteristics plot is given below. The current voltage characteristics. When, V is positive the junction is forward biased and when V is negative, the junction is reversing biased. When V is negative and less than VTH, the current is very small. But when V exceeds VTH, the current suddenly becomes very high. The voltage VTH is known as threshold or cut in voltage. For Silicon diode VTH = 0.6 V.
At a reverse voltage corresponding to the point P, there is abrupt increment in reverse current. The PQ portion of the characteristics is known as breakdown region.