Question

If the ratio of the concentration of electrons and that of holes in a semiconductor is $7 / 5$ and the ratio of their currents is $7 / 4$ , then the ratio of their drift velocities is

• A. $4 / 7$
• B. $5 / 8$
• C. $4 / 5$
• D. $5 / 4$

Answer 1

Answer: (D)

Drift velocity $v_{\text{d}}=\frac{I}{\textit{nAe}}$
$\frac{\left(v_{d}\right)_{electron}}{\left(v_{d}\right)_{hole}}=\left(\frac{I_{e}}{I_{h}}\right)\left(\frac{n_{h}}{n_{e}}\right)=\frac{7}{4}\times \frac{5}{7}=\frac{5}{4}$
Hence, the ratio of their drift velocities is $\frac{5}{4}$