The three different layers of a transistor are made of a different semiconductor material. Two out of three are doped in to give n-type or p-type, and one remaining layer is opposite of the other two layers. The layers are arranged in such a way that two similar layer sandwich the layer of opposite type. This gives two types of arrangement of layers in transistors namely P-N-P type and N-P-N type.
The names for these three different layers are given below-
- Emitter: It emits the charge carriers.
- Collector: It collects the charge carriers.
- Base: it is the region between emitter and collector.
In PNP transistors the sequence of doped regions is-
- p-region collector
- n-region base
- p-region emitter
In NPN transistor the sequence of doped regions is-
- n-region collector
- p-region base
- n-region emitter