119. Thermistors and photo resistances

Thermistors.

In semiconductors, electrical resistance is highly dependent on temperature. This property is used to measure temperature by the value of electrical current in a semiconductor circuit. These devices are called thermistors.

Photoresistances.

The electrical conductivity of semiconductors does not only increase when heated. The conductivity of semiconductors also increases when they are illuminated by light. You can notice that when a semiconductor is illuminated, the electric current in the circuit increases markedly. This indicates an increase in the conductivity (decrease in resistance) of semiconductors under the influence of light. This effect is not related to heating, as it can also be observed at a constant temperature. Electrical conductivity increases due to broken bonds and the formation of free electrons and holes caused by the light energy falling on the semiconductor. This phenomenon is called the photoelectric effect.

Devices that use the photoelectric effect in semiconductors are called photoresistance. Small sizes and high sensitivity of photoresistances allow to use them in the most various areas of technology.