Question

The temperature coefficient of resistance of a semiconductor is

Answer 1

Coefficients approaching zero can be obtained by alloying certain metals. A negative coefficient for a material means that its resistance decreases with an increase in temperature. Semiconductormaterials (carbon, silicon, germanium) typically have negative temperature coefficients of resistance.

Answer 2

In metal if temperature is increased, the random motion of charged particles increases which result to more collisions. More collision resist smooth flow of electrons through the metal, hence the resistance of the metal increases with the increase in temperature. So, temperature coefficient of resistance is considered as positive for metal.

But in case of semiconductor , the number of free electrons increases with increase in temperature. Because at higher temperature, due to sufficient heat energy supplied to the crystal, more numbers of covalent bonds are broken and hence more free electrons are created.

That means if temperature increases, more number of electrons comes to the conduction bands from valance band by crossing the forbidden energy gap. As the number of free electrons increases, the resistance of this type of non-metallic substance decreases with increase of temperature.

Hence temperature coefficient of resistance is negative for semiconductors.