Structure and Action of Transistor: A transistor is a three-terminal semiconductor device that is used to amplify or switch electronic signals. It is made up of two junctions between two differently doped regions of a semiconductor material, typically silicon. The two most common types of transistors are bipolar junction transistors (BJTs) and field-effect transistors (FETs).

Structure and Action of Transistor

Bipolar Junction Transistor (BJT): A BJT consists of three layers of semiconductor material: a p-type layer sandwiched between two n-type layers (NPN transistor) or an n-type layer sandwiched between two p-type layers (PNP transistor). The layers are arranged in a sandwich-like structure with two junctions: a base-emitter junction and a base-collector junction.

The base-emitter junction is forward-biased, meaning that a small current flows from the emitter to the base. This causes a larger current to flow from the collector to the emitter, which is controlled by the current flowing into the base. The transistor is used as an amplifier when a small signal voltage is applied to the base, causing a larger output voltage to appear across the collector-emitter junction.

When the base-emitter junction is reverse-biased, the transistor is in its off state and no current flows through the collector-emitter junction. When the base-emitter junction is forward-biased, the transistor is in its on state and current flows from the collector to the emitter.

Field-Effect Transistor (FET): A FET consists of a semiconductor channel between two heavily doped regions called the source and drain. The channel is covered by a gate electrode that is separated from the channel by a thin insulating layer, usually made of silicon dioxide.

The gate electrode is used to control the flow of current through the channel by applying a voltage to the gate. When a positive voltage is applied to the gate, an electric field is created that attracts electrons to the surface of the channel, creating a conductive path between the source and drain. This is called the enhancement mode.

In the depletion mode, the channel is already conductive due to the presence of dopants, and the gate voltage is used to control the width of the conductive region. When a negative voltage is applied to the gate, the electric field created by the gate repels electrons from the surface of the channel, creating a depletion region that reduces the width of the conductive path.

Overall, both BJTs and FETs use the principle of controlling the flow of current through a semiconductor material to amplify or switch electronic signals. The specific mechanism of current control differs between the two types of transistors, but they share a common structure of a semiconductor channel with at least one junction or electrode that controls the current flow.

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By Team Learning Mantras