# Define Intrinsic semiconductor? Effect of Temperature – Direct & Indirect band gap

## Intrinsic semiconductor

An intrinsic or pure semiconductor also called an undoped semiconductor. It is a pure semiconductor without any doping species present. So the number of charge carriers is therefore determined by the properties of the material itself, instead of the number of impurities.

In intrinsic semiconductors the number of holes and excited electrons are equal.

The semiconductor remains intrinsic after doping, only if it is doped with both donors and acceptors equally. In this case, the numbers of electrons are equal to the numbers of holes, and the semiconductor remains intrinsic, though doped. The electrical conductivity of an intrinsic semiconductor can be due to the excited state of electrons.

In intrinsic semiconductors, the number of holes in the valence band is equal to the number of electrons in the conduction band.

### Indirect band gap

An indirect band gap in the intrinsic semiconductor is one in which the maximum energy of the valence band occurs at a different k (k-space wave vector) than the minimum energy of the conduction band. Examples include silicon and germanium.

### Direct band gap

A direct band gap in the intrinsic semiconductor is one where the maximum energy of the valence band is equal to the minimum energy of the conduction band. Examples include gallium arsenide.

### Effect of Temperature on Intrinsic Semiconductor

A silicon crystal is differing from the insulator because at the temperature that is above the absolute zero. There is a non-zero probability that an electron will be knocked loose from its position, leaving behind an electron deficiency called a “hole”. Small current flow if a voltage is applied then both the electron and the hole can contribute to producing the current.

The conductivity of a semiconductor can be explained in terms of the band theory of solids. The band model of a semiconductor suggests that there is a finite possibility that electrons can reach the conduction band and contribute to electrical conduction at ordinary temperatures. On the basis of the energy band energy level, the intrinsic semiconductor at absolute zero temperature is shown below by figure.

In intrinsic semiconductor the valence band is completely filled and the conduction band is completely empty.

When the temperature increases and some heat energy are supplied to the semiconductor, some of the valence electrons are jumped to conduction band leaving behind holes in the valence band as shown below.

The electrons reaching at the conduction band move freely throughout the medium. The holes also free to move anywhere that created in the crystal. This behavior of the semiconductor shows the negative temperature coefficient of resistance. This means that when the temperature increases, the conductivity increases and resistivity of the material decreases. Electrons and holes Above absolute zero temperatures, the intrinsic semiconductor such as silicon, there will be some electrons that are excited and jump from band gap into the conduction band.

That can support the charge flowing. When the electron in pure silicon crosses the band gap or energy level, it leaves behind an electron vacancy or “hole” in the regular silicon lattice. When external voltage is applied, both the electron and the hole can easily move across the material. In an N-type semiconductor, the doping contributes extra electrons that dramatically increasing the conductivity of the material.

In a P-type semiconductor, the doping produces extra vacancies or holes, which also increase the conductivity. It is, however, the behavior of the P-N junction which is the key to the different variety of solid-state electronic devices.

### Semiconductor current

The current which will flow consists of both electron and holes in an intrinsic semiconductor. That is, the electrons which have been free from their lattice positions into the conduction band can move freely through the material. In addition, other electrons can exist between lattice positions to fill the vacancies left by the free electrons.

This additional process is called holes conduction because it is as if the holes are migrating across the material in the direction opposite to the free electron movement. This current is highly dependent on temperature.