What experience shows that the resistivity of a semiconductor decreases with increasing temperature?

Let’s assemble an electrical circuit from a current source, a galvanometer, a germanium semiconductor on the panel and a key. Having closed the circuit, we will not notice the deviation of the galvanometer needle, that is, there are no free charge carriers in the circuit. If we heat a germanium semiconductor over the flame of an alcohol lamp (the flame should not touch the device), we will see that the galvanometer needle will deviate. Consequently, an electric current is generated in the circuit. From experience, we can conclude that the resistivity of a semiconductor decreases with increasing temperature.

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