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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


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




Elemental semiconductors: Si and Ge

Compound semiconductors:


Intrinsic semiconductor

A semiconductor in its pure state is called intrinsic semiconductor.

In its crystalline structure, every Si or Ge atom tends to share one of its four valence electrons with each of its four nearest neighbour atoms, and also to take share of one electron from each such neighbour.

Effect of temperature on conductivity of semiconductors

As the temperature increases, more thermal energy becomes available to these electrons and some of these electrons may break away (becoming free electrons contributing to conduction).

The thermal energy ionises only a few atoms in the crystalline lattice and creates a vacancy in the bond. The neighbourhood, from which the free electron (with charge –q) has come out leaves a vacancy with an effective charge (+q ). This vacancy with the effective positive electronic charge is called a hole.




An intrinsic semiconductor will behave like an insulator at T = 0 K.

At higher temperatures (T > 0K), some electrons are excited and move from the valence band to the conduction band.


In intrinsic semiconductors, the number of free electrons, ne is equal to the number of holes, nh. That is,

ne = nh= ni 

Where, ni is called intrinsic carrier concentration.

Both electrons and holes move to conduct.

Also, I = Ie + Ih, where Ie is the current due to movement of free electrons and Ih is the current due to movement of holes.

Extrinsic semiconductor

A semiconductor doped with suitable impurity, is called extrinsic semiconductor. The deliberate addition of a desirable impurity is called doping and the impurity atoms are called dopants.

On the basis of doped impurity extrinsic semiconductors are of two types, i.e., m-type and p-type.