Electric current in semiconductors

The electric current in semiconductors is the directed motion of holes and electrons, which is affected by the electric field.

As a result of the experiments, it was noted that the electric current in semiconductors is not accompanied by the transfer of matter - no chemical changes occur in them. Thus, electrons can be regarded as current carriers in semiconductors.

The ability of a material to form an electric current in it can be determined by the specific electrical conductivity. In this indicator, conductors occupy an intermediate position between conductors and dielectrics. Semiconductors are different types of minerals, some metals, metal sulphides, etc. The electric current in semiconductors arises because of the concentration of free electrons that can be directed in the substance. Comparing metals and conductors, it can be noted that there is a difference between the temperature effect on their conductivity. Increasing the temperature leads to a decrease in the conductivity of metals. In semiconductors, the conductivity index increases. If the temperature in the semiconductor increases, the motion of free electrons will be more chaotic. This is due to an increase in the number of collisions. However, in semiconductors, compared with metals, the free electron concentration index is significantly increased. These factors have the opposite effect on the conductivity: the more collisions, the lower the conductivity, the higher the concentration, the higher it is. In metals, there is no relationship between the temperature and the concentration of free electrons, so that with the change in conductivity with increasing temperature, only the possibility of an ordered displacement of free electrons is reduced. As for semiconductors, the effect of increasing concentration is higher. Thus, the greater the temperature, the greater the conductivity.

There is a relationship between the motion of charge carriers and the notion of electric current in semiconductors. In semiconductors, the appearance of charge carriers is characterized by various factors, among which the most important are the temperature and purity of the material. By purity, semiconductors are divided into impurity and intrinsic.

As for its own conductor, the influence of impurities at a certain temperature can not be considered significant for them. Since the width of the forbidden band is small in semiconductors, in the intrinsic semiconductor, when the temperature reaches absolute zero, the valence band completely fills up with electrons. But the conduction band is completely free: it does not have electrical conductivity, and it functions as an ideal dielectric. At other temperatures, there is a possibility that, for thermal fluctuations, certain electrons can overcome the potential barrier and find themselves in the conduction band.

The Thomson effect

The principle of the thermoelectric effect of Thomson: when an electric current is passed in semiconductors along which there is a temperature gradient, in them, in addition to Joule heat, additional heat will be released or absorbed, depending on the direction in which the current flows.

Insufficiently uniform heating of a sample having a homogeneous structure affects its properties, as a result of which the substance becomes inhomogeneous. Thus, the Thomson phenomenon is a specific phenomenon of Pellet. The only difference is that the different non-chemical composition of the sample, and the non-ordinary nature of the temperature causes this heterogeneity.