Question

Pure silicon at 300 K has equal electron (n$_e$) and hole (n$_h$) concentration of $1.5 \times 10^{16} m^{-3}$. Doping by indium increases $n_h$ to $4.5 \times 10^{22}m^{-3}$ The $n_e $ in the doped silicon is

• A. $9 \times 10^5$
• B. $5 \times 10^9$
• C. $2.25 \times 10^{11}$
• D. $3 \times 10^{19}$

Answer 1

Answer: (B)

In an extrinsic semiconductor
$ \, \, \, \, \, \, \, n_en_h =(n_i)^2$
$n_e \times 4.5 \times 10^{22} =(1.5 \times 10^{16})^2 $
$ \, \, \, \, \, \, \, \, n_e =\frac{2.25 \times 10^{32}}{4.5 \times 10^{22}}$
$ \, \, \, \, \, \, \, \, n_e =5 \times 10^9$