An electric field is applied to a semiconductor. Let the number of charge carries be n and the average drift speed by v. If the temperature is increased,
(a) both n and v will increase
(b) n will increase but v will decrease
(c) v will increase but n will decrease
(d) both n and v will decrease.

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Solution

(b) n will increase but v will decrease

As we increase the temperature, additional electron‒hole pairs are created in a semiconductor. As a result, the number of charge carriers increases.
Now, drift velocity $(v_{d})$ is given by
$v_{d} = \frac{- e E τ}{m}$
As the temperature increases, the relaxation time of charge carriers $(τ)$ decreases. As a result, v_d decreases.

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