The doping concentrations on the $p$-side and $n$-side of a silicon diode are $1\times 10^{16}\:cm^{-3}$ and $1\times 10^{17}\:cm^{-3},$ respectively. A forward bias of $0.3\:V$ is applied to the diode. At $T = 300\:K,$ the intrinsic carrier concentration of silicon $n_{i} = 1.5\times 10^{10}\:cm^{-3}$ and $\dfrac{kT}{q} = 26\:mV.$ The electron concentration at the edge of the depletion region on the $p$-side is
1.  $2.3\times 10^{9}\:cm^{-3}$
2. $1\times 10^{16}\:cm^{-3}$
3. $1\times 10^{17}\:cm^{-3}$
4. $2.25\times 10^{6}\:cm^{-3}$