Question

The ratio of electron and hole currents in a semiconductor is $7/4$ and the ratio of drift velocities of electrons and holes is $5/4$, then the ratio of concentrations of electrons and holes will be

• A. $5/7$
• B. $7/5$
• C. $25/49$
• D. $49/25$

Answer 1

Answer: (B)

$7/5$

$I=nAev$${}_d$ or $I$$\propto$ $nv$${}_d$

$\therefore \frac{I_e}{I_h}=\frac{n_e{v}_e}{n_h{v}_h}or\frac{n_e}{n_h}$

$=\frac{I_e}{I_h}\times \frac{v_h}{v_e}$

$=\frac{7}{4}\times \frac{4}{5}=\frac{7}{5}$