## Fermi level in semiconductors

The concept of Fermi Level:

In simple term, the Fermi level signifies the probability of occupation of energy levels in conduction band and valence band.

In extrinsic semiconductors, the number of electrons in the conduction band and the number of holes in the valence band are not equal.

## How full wave rectifier operates

Let us discuss today the operation of full wave rectifier:

In the full wave rectifier, two PN junction Diodes (say D1 and D2) a connected in the circuit. A load resistance (RL) is connected in the circuit across which the output is taken.

Let at any instant S1 is positive and S2 is negative. the diode (D1) is forward biased and diode (D2) is reversed biased so D1 will conduct but D2 will not. Continue reading “How full wave rectifier operates”

## Half wave rectifier operation

Rectifier:

A rectifier is a device that converts alternating current into direct current.

Half wave rectifier:

In this rectifier, the PN junction diode is connected to an input AC supply with the help of a primary coil, which will induce an emf in the secondary coil and ultimately the output is taken across the load resistance (RL).

Let at any instant S1 is positive and S2 is negative. Due to this polarity the junction diode is forward biased so it will start conducting and output is obtained. Continue reading “Half wave rectifier operation”

## How depletion layer or potential barrier is formed in the PN junction diode

In a PN junction diode holes are the majority carriers on P side whereas electrons are the majority carriers on n-side. The process of diffusion takes place due to which the majority carriers diffuse from one region to the other so the P-region becomes less positive and the n-region becomes less negative.

An imaginary battery is developed across the junction which prevents further movement of majority carriers and the voltage so developed is known as the potential barrier. The layer is known as the depletion layer. Continue reading “How depletion layer or potential barrier is formed in the PN junction diode”

## Difference between forward biasing and reverse biasing

To start the discussion of discussion of difference between forward biasing and reverse biasing, first of all let us discuss the meaning of PN junction diode and biasing:

The combination of the p-type material or semi-conductor with the n-type semi-conductor results in a PN junction Diode.

Biasing: The biasing of a diode means to make junction operative. In other words biasing means to connect an external to pn junction diode. The battery can be connected by two methods, one is known as forward biasing and second is known as reverse biasing. Let us discuss them one by one: Continue reading “Difference between forward biasing and reverse biasing”

## Derivation of expression for the conductivity of a Semi-Conductor

Last time we have discussed the conductivity of semiconductor. Let us today derive the expression the expression for conductivity of semiconductor.

In a Semi-Conductor of length (ℓ) and area of Cross-Section. Let ne and nh be the no. of electrons and holes with drift velocities Ve and Vh respectively.

So, the total current in the semi-conductor will be the sum of current due to electrons as well as holes,

i.e.        I = Ie + Ih                                                             (i) Continue reading “Derivation of expression for the conductivity of a Semi-Conductor”

## How conductivity of semiconductor is increased

The conductivity of semiconductor can be increased by the following methods:

1. By doping: The addition of impurity atoms to a pure-semi-conductor is known as doping. The doping is done to increase the conductivity of a pure semi-conductor. It must be noted that the impurity atom is about 1 in every 1010 atoms. Continue reading “How conductivity of semiconductor is increased”

## meaning of the term hole in a semi-conductor

Hole in a semiconductor:

In a semi-conductor the energy gap is of the order of 1eV. At OK, the semi-conductor behaves like an insulator but at room temp the electrons acquire sufficient energy to jump to the conductor band thereby creating a vacancy in the valence band.

This deficiency or vacancy of electron in the valence band is termed as a hole. It is equivalent to 1 unit of +Ve charge. To fill this vacancy, the nearly electrons present in the valence band jumps to that position. So another hole is created and thus it appears as if the holes are moving. So, in R semi-conductor, electrons move in the conduction band whereas holes in the valence band.

Why doping is done in semiconductors?

The addition of impurity atoms to a pure-semi-conductor is known as doping. The doping is done to increase the conductivity of a pure semi-conductor. It must be noted that the impurity atom is about 1 in every 1010 atoms.