Question
Thu November 10, 2011 By:

How is it so that the resistivity of a semiconducter decreases with the increase in temperature whereas the resistivity of a metal increases with the increase in temperature? Regards, Sharmistha Panda

Expert Reply
Fri November 11, 2011
Conductivity of a material depends directly both on the number n of free electrons per unit
volume and on the average time ? between collisions. As we increase temperature, average speed of the electrons, which act as the carriers of current, increases resulting in more frequent collisions. The average time of collisions ?, thus decreases with temperature which decreases conductivity of metals. In semiconductors the number of free electrons increases with increasing tempreture,thus increasing conductivity
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