Question

An electric field is applied to a semiconductor. Let the number of charge carries be $n$ and the average drift speed by $v_d$. If the temperature is increased, then

• A. both $n$ and $v_d$ will increase.
• B. $n$ will increase, but $v_d$ will decrease.
• C. $v_d$ will increase, but $n$ will decrease.
• D. both $n$ and $v_d$ will decrease.

Answer 1

The correct option is B $n$ will increase, but $v_d$ will decrease.

As we increase the temperature, additional electron-hole pairs are created in the semiconductor.

As a result, the number of charge carriers $\left(n\right)$ increases.

Now, drift velocity $\left(v_d\right)$ is given by

$v_d=\frac{eE\tau }{m}$

As $\text{temperature}\uparrow \text{relaxation time}\left(\tau \right)\downarrow \therefore v_d\uparrow$

Hence, option $\left(B\right)$ is correct.