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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 14 SEMICONDUCTORS

Types of substances on the basis of conductivity

Metals on the basis of conductivity

Semiconductors on the basis of conductivity

Insulators on the basis of conductivity

Energy bands in solids

Valence band

Conduction band

Forbidden band

Types of substances on the basis of energy bands

Metals on the basis of energy bands

Insulators on the basis of energy bands

Semiconductors on the basis of energy bands

Types of semiconductors

Elemental semiconductors

Compound semiconductors

Types of semiconductors based on purity

Intrinsic semiconductors

Effect of temperature on conductivity of semiconductors

Extrinsic semiconductor

n-type semiconductor

p-type semiconductor

Conductivity of extrinsic semiconductor

p-n junction

Diffusion of charge

Diffusion current

Depletion region

Drift of charge carriers

Drift current

Potential barrier across p-n junction

Semiconductor diode

Forward bias of p-n junction

Reverse bias of p-n junction

V-I characteristics of a diode

Threshold voltage or cut-in voltage

Dynamic resistance of diode

Application of junction diode as a rectifier

Half wave rectifier

Full-wave rectifier

Centre-tap transformer

Electric filter

Role of capacitor in the filter

Some special type of diodes

Zener diode

Zener diode as voltage regulator

Photodiode

Light emitting diodes (LED)

Photovoltaic devices (Solar cells)

Junction transistor

n-p-n transistor

p-n-p transistor

Transistor emitter

Transistor base

Transistor collector

Transistor in saturation region

Transistor in cut-off region

Transistor in active region

Basic transistor circuit configurations and transistor characteristics

Transistor in common base configuration

Transistor in common emitter configuration

Common emitter transistor characteristics

Input resistance of transistor

Output resistance of transistor

Current amplification factor

Transistor as a device

Transistor as a switch - base-biased CE configuration

Transistor as an amplifier

Amplification of dc voltage

Amplification of ac signal

Feedback amplifier

Transistor oscillator

Working of feedback amplifier

Tank circuit

Digital electronics

Analog signal

Digital signal

Logic gates

NOT gate

OR gate

AND gate

NAND gate

NOR gate

Integrated circuits

Linear or analogue ICs

Digital ICs

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 14 SEMICONDUCTORS

p-n junction

An arrangement, consisting of a p-type semiconductor brought into a close contact with n-type semiconductor, is called a p -n junction.

Diffusion of charge and diffusion current

During the formation of p-n junction, and due to the concentration gradient across p-, and n- sides, holes diffuse from p-side to n-side (p→n) and electrons diffuse from n-side to p-side (n→p) and a diffusion current is setup across the junction.

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p-n junction formation

Depletion region

Due to diffusion of holes p→n and electrons n→p, a –ve region is created on p-side and a +ve region is created on n-side.

This space-charge region on either side of the junction together is known as depletion region and net charge in this region is 0.

Due to the positive space-charge region on n-side of the junction and negative space charge region on p-side of the junction, an electric field directed from positive charge towards negative charge develops. Due to this field, an electron on p-side of the junction moves to n-side and a hole on n-side of the junction moves to p-side.

Drift of charge carriers and drift current

The motion of charge carriers due to the electric field is called drift and current is called drift current.

Initially, diffusion current is large and drift current is small. As the diffusion process continues, the space-charge regions on either side of the junction extend, thus increasing the electric field strength and hence drift current. This process continues until the diffusion current equals the drift current and p-n junction is formed. In a p-n junction under equilibrium there is no net current.

The loss of electrons from the n-region and the gain of electrons by the p-region; causes a difference of potential across the junction of the two regions. The polarity of this potential is such as to oppose further flow of carriers so that a condition of equilibrium exists.

Potential barrier across a p-n junction

The potential difference across the depletion layer is called potential barrier (Vo).

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