Question

An abrupt pn junction at T=300K and at zero bias has fermi-level in n-side is 5 kT above the intrinsic fermi-level, then the value of dopant concentration will be
$\text{Assume}{n}_i=1.5\times {10}^{10}c{m}^{-3}$

• A. $3.25\times {10}^{14}{\text{cm}}^{-3}$
• B. $1.5\times {10}^{12}{\text{cm}}^{-3}$
• C. $2.23\times {10}^{12}{\text{cm}}^{-3}$
• D. $1.72\times {10}^{14}{\text{cm}}^{-3}$

Answer 1

The correct option is C $2.23\times {10}^{12}{\text{cm}}^{-3}$

Ans : (c)

$\text{Given,}{E}_{Fn}-E_{Fi}=5kT$
$\text{but,}{E}_{Fn}-E_{Fi}=KT\text{In}\left[\frac{N_d}{n_i}\right]$
$5KT=KT\text{In}\left[\frac{N_d}{n_i}\right]$
$5=\text{In}\left[\frac{N_d}{1.5\times {10}^{10}}\right]$
$\therefore N_d=2.23\times {10}^{12}{\text{cm}}^{-3}$