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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-type semiconductor

This is obtained when Si or Ge is doped with a trivalent impurity like Al, B, In, etc. The dopant has one valence electron less than Si or Ge. This atom can form covalent bonds with neighbouring three Si atoms but does not have any electron to offer to the fourth Si atom. So the bond between the fourth neighbour and the trivalent atom has a vacancy or hole.

Since the neighbouring Si atom in the lattice needs an electron in place of a hole, an electron in the outer orbit of an atom in the neighbourhood may jump to fill this vacancy, leaving a vacancy or hole at its own site and the moves increasing the conductivity.

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The trivalent foreign atom becomes effectively negatively charged when it shares fourth electron with neighbouring Si atom. Therefore, the dopant atom of p-type material can be treated as core of one negative charge along with its associated hole.

These holes are in addition to the intrinsically generated holes while the source of conduction electrons is only intrinsic generation. Thus, for such a material, the holes are the majority carriers and electrons are minority carriers.

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