Answer:
A transistor is a three-terminal device consisting of 3 layers of semiconductor material. Two of them are one type of semiconductor and the third, a different type. For example, a PNP transistor consists of 2 layers of P-type semiconductor and a layer of N-type semiconductor between them. We can also have the NPN type transistor which has 2 layers of N-type semiconductor and a layer of P-type semiconductor between them. The three terminals are respectively referred to as emitter, base and collector. Transistors are widely used electronic components that perform the function of a switch or an amplifier.
The semiconductor material used in transistors is generally silicon, germanium or gallium arsenide. Impurities are added to them in order to create electrically positive (P) or electrically negative (N) behavior. When these layers are joined together the contact potential creates a potential barrier across the PN or NP junction. This potential barrier maintains electrons on the N side and holes on the P side.
NPN stands for negative positive negative PNP stands for positive negative positive. GALLIUM ARSENIDE is only used on LEDS manufacturing not transistors
ANSWER: NPN negative positive negative SUBSTRATE PNP is opposite of NPN