Question

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

• A. $4\mu m$
• B. $12\mu m$
• C. $4.9\mu m$
• D. $8\mu m$

Answer 1

The correct option is A $4\mu m$

Ans : (a)

Junction potential = Built in potential + reverse bias voltage
$V_j=V_0+V_R$
Now for abrupt pn-junction depletion width
$W\propto V_j^{1/2}$
$W=K{V}_j^{1/2}$
$2\mu m=K(0.8+1.2{)}^{1/2}$......(i)
$x=K(0.8+7.2{)}^{1/2}$..............(ii)

From (i) & (ii) $x=4\mu m$