A p-n-p transistor is a type of bipolar junction transistor (BJT) that consists of three layers of semiconductor materials. The layers are composed of two p-type (positive) regions sandwiching one n-type (negative) region. This arrangement gives the transistor its name, "p-n-p," indicating the order of the layers.
The p-n-p transistor has three terminals: the emitter (E), the base (B), and the collector (C). The emitter is made of heavily doped p-type material and is the source of majority carriers (holes) in the transistor. The collector is made of moderately doped p-type material and is responsible for collecting these majority carriers. Between the emitter and collector lies the base, which is made of n-type material. The base controls the flow of majority carriers from the emitter to the collector.
By applying a small forward bias voltage to the base-emitter junction, the p-n-p transistor can be operated in an active region. This allows controlled amplification of electrical signals. The majority carriers injected from the emitter to the base combine with the minority carriers (electrons) in the base, resulting in a current flow from the emitter to the collector. The collector current is typically many times larger than the base current, providing amplification.
P-n-p transistors are commonly used in electronic circuits for amplification, switching, and other functions. They are essential components in various electronic devices, such as audio amplifiers, voltage regulators, and logic gates.
The term "p-n-p transistor" is derived from the etymology of its components and their functionality.
The "p" and "n" in the term refer to the two types of semiconductors used in the transistor: "p-type" and "n-type" semiconductors. "P-type" semiconductors are doped with impurities that create positively charged "holes" where an electron is missing, while "n-type" semiconductors are doped with impurities that introduce extra electrons.
The term "transistor" is a combination of "transfer" and "resistor", indicating its function of transferring an electrical signal across a device. It is essentially a semiconductor device that can amplify or switch electronic signals and electrical power.