What is p n p transister

A PNP transistor is obtained by sandwiching a thin block of N-type semiconductor in between two blocks of P-type semiconductor. A thin block of P-type semiconductor sandwiched in between two blocks of N-type semiconductor forms a NPN transistor. The three sections of the transistor are emitter (E), base (B) and collector (C).

The emitter region is heavily doped and its size is moderate. The emitter supplies a large number of majority carriers for the current flow. The base region is very thin and lightly doped. Base region is in between the emitter and collector region. The collector region is moderately doped and larger in size than the emitter. The collector collects the majority carriers supplied by the emitter. The emitter and collector regions cannot be interchanged.
When a transistor is connected in a circuit, the base-emitter junction is always forward biased and the base-collector junction is always reverse biased.

In the given PNP transistor circuit, the emtter-base junction is forward biased and hence, large number of holes flow from the emitter region to the base region. This causes the emitter current (IE). When the holes diffuse into the base region, only a few holes combine with electrons. The base region is very thin and lightly doped and has a low number density of electrons. Thus, a very small current flows through the base region called the base current (IB). The remaining holes reach the collector under the influence of the negative collector voltage. This produces a current in the collector region called the collector current (IC).