An electric current in semiconductors is the directional movement of holes and electrons, which is influenced by an 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 - they do not undergo any chemical changes. Thus, electrons can be considered current carriers in semiconductors.
The ability of a material to form an electric current in it can be determined by electrical conductivity. According to this indicator, conductors occupy an intermediate position between conductors and dielectrics. Semiconductors are various types of minerals, some metals, metal sulfides, etc. The electric current in semiconductors arises due to the concentration of free electrons that can move in a directional direction in matter. Comparing metals and conductors, it can be noted that there is a difference between the temperature effect on their conductivity. An increase in temperature leads to a decrease in the conductivity of metals. In semiconductors, the conductivity index increases. If the temperature in a semiconductor increases, then the motion of free electrons will be more chaotic. This is due to an increase in the number of collisions. However, in semiconductors, in comparison with metals, the concentration of free electrons increases significantly. These factors have the opposite effect on conductivity: the more collisions, the less conductivity, the higher the concentration, the higher it is. In metals there is no relationship between temperature and the concentration of free electrons, so that with a change in conductivity with increasing temperature, the possibility of an ordered movement of free electrons only decreases. For semiconductors, the effect of increasing concentration is higher. Thus, the more the temperature rises, the greater the conductivity.
There is a relationship between the movement of charge carriers and such a concept as electric current in semiconductors. In semiconductors, the appearance of charge carriers is characterized by various factors, among which the temperature and purity of the material are especially important. By purity, semiconductors are divided into impurity and intrinsic.
As for its own conductor, the effect of impurities at a certain temperature cannot be considered significant for them. Since the band gap in semiconductors is small, in the semiconductor proper, when the temperature reaches absolute zero, the valence band is completely filled with electrons. But the conduction band is completely free: there is no electrical conductivity in it, and it functions as an ideal dielectric. At other temperatures, there is a possibility that, with thermal fluctuations, certain electrons can overcome the potential barrier and end up in the conduction band.
Thomson effect
The principle of the Thomson thermoelectric effect: when electric current is passed in semiconductors along which there is a temperature gradient, in addition to the Joule heat, additional heat will be released or absorbed depending on the direction the current will flow.
Insufficiently uniform heating of a sample having a uniform structure affects its properties, as a result of which the substance becomes inhomogeneous. Thus, the Thomson phenomenon is a specific Pelté phenomenon. The only difference is that the different, not the chemical composition of the sample, but the eccentricity of the temperature causes this heterogeneity.