Name: Energy Band Gap
Uploaded: 2019-07-19
Duration: 5 min 21 s
Description: We know that certain materials conduct electricity whereas some don’t. Has it got anything to do with their energy bandgap? Let’s find out in this video.

Question

Describe the construction of

p n p

and

n p n

transistor with diagrams and explain their schematic symbols.

Accepted Answer

Construction Of P-N-P Transistor

P-type semiconductors, which represent the emitter and collector, are doped heavily than N-type semiconductors, which represent the base. Hence, the depletion region at both junctions penetrates towards the N-type layer.

In P-N-P transistors, in this type of transistor, majority charge carriers are holes, and minority charge carriers are electrons. The emitter emits holes and is collected at the collector.

In a P-N-P transistor, the base current which enters into the collector is amplified. The flow of current is typically controlled by the base. Current flows in the opposite direction in the base. In a P-N-P transistor, the emitter emits “holes”, and these holes are collected by the collector.

The base region features many free electrons. But, the width of the middle layer is very small and is lightly doped. So significantly less free electrons are present in the base region.

Schematic Symbol : P-N-P transistors representation is as shown in the figure below.

This bipolar P-N-P junction transistor is formed with three layers of semiconductor material, with two P-type regions and one N-type region. It includes three terminals:

Emitter

Collector

Base

Emitter – emitter part in a transistor lets it supply majority charge carriers. The emitter is always forward biased with respect to the base. Hence, the majority of charge carriers are supplied to the base. The emitter of a transistor is heavily doped and moderate.

Collector – the majority of the charge carrier supplied by the emitter is collected by the collector. The collector-base junction is always reverse biased. The collector area is moderately doped and has the capacity to collect the charge carrier supplied by the emitter.

Base – The centre section of the transistor is known as the base. The base forms two circuits, the input circuit with the emitter and the output circuit with the collector. The emitter-base is forward biased and offers low resistance to the circuit. The collector-base junction is in reverse bias and offers higher resistance to the circuit. The base of a transistor is lightly doped and very thin, due to which it offers the majority charge carrier to the base.

Depletion region –The depletion region are formed at the emitter-base junction and the base-collector junction.

Construction Of N-P-N Transistor

The N-P-N transistor is made of semiconductor materials like silicon or germanium. When a p-type semiconductor material is fused between two n-type semiconductor materials, an N-P-N transistor is formed.

The N-P-N transistor features three terminals: emitter, base and collector. This transistor features two diodes that are connected back to back. The diode seen between the emitter-base terminal is referred to as the emitter-base diode. The diode between collector and base terminal is known as collector-base diodes. The emitter is moderately doped, the base is lightly doped, and the collector is comparatively more doped.

Schematic Symbol : The N-P-N transistor consists of two n-type semiconductors that sandwich a p-type semiconductor. Here, electrons are the majority charge carriers, while holes are the minority charge carriers. The N-P-N transistor is represented, as shown below.

In the above figure, we can see an arrow pointing outwards from the emitter terminal. This indicates the direction of the flow of current through the device.

Describe the construction of $p n p$ and $n p n$ transistor with diagrams and explain their schematic symbols.

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