# Semiconductor Physics (Things you should know)

1. Resistance of a pure semiconductor is millions and millions of times greater then that of a good conductor like copper.
2 Charge carriers in semiconductors are electrons(-e) and holes(p having charge equal to +e).
3 Pure semiconductor known as intrinsic semiconductor contains equal number of both holes and electrons.
4 Drift velocity of electrons is greater then that of holes.
5 Taking both charge carriers in semiconductor into account current is given as I=neA(vn+vp) where n is number of holes and electrons, vn is the drift velocity of electrons and vp is drift velocity of holes and A is the cross-sectional area.
6 Electrical resistance of pure semiconducter decreases with increase in temperature.
7 Semiconductors can be doped with a tiny amount of impurity such as one part in a million to form an impure or extrinsic semiconductor.
8 p-type semiconductor is a type of ectrinsic semiconductor formed when pure semiconductor is doped with trivalent element (for ex- indium). It has large majority of holes and small minority of electrons. Thus majority charge carriers in a p-type semiconductor are holes.
9 n-type semiconductor is a type of ectrinsic semiconductor formed when pure semiconductor is doped with pentavalent element (for ex- phosphorus). It has large majority of electrons and small minority of holes. Thus majority charge carriers in a p-type semiconductor are electrons.
10 Junction diode is a simplest kind of semiconductor device. It has a pn junction and consists of a p-type crystal and n-type crystal and is formed by growing n-type semiconductor over p-type semiconductor. Junction diodes are used as rectifiers.
11 Bipolar junction transistor is a three terminal device. There are two type of transistors npn and pnp transistor. Three terminals of the transistor are joined to base, emitter and collector of the transistor.
12 With Common emitter transistor, the base current Ib is the input current and the