A $p^{+} n$ junction has a built-in potential of $0.8 \mathrm{~V}$. The depletion layer width at a reverse bias of $1.2 \mathrm{~V}$ is $2 \; \mu \mathrm{m}$. For a reverse bias of $7.2 \mathrm{~V},$ the depletion layer width will be
- $4 \; \mu \mathrm{m}$
- $4.9 \; \mu \mathrm{m}$
- $8 \; \mu \mathrm{m}$
- $12 \; \mu \mathrm{m}$