Question

$A$ certain $p -n$ junction, having a depletion region of width $20 \mu$ m, was found to have a breakdown voltage of $100\, V.$ If the width of the depletion region is reduced to $1\, \mu$ m during its production, then it can be used as a zener diode for voltage regulation of

• A. 5 V
• B. 10 V
• C. 7.5 V
• D. 2000 V

Answer 1

Answer: (B)

Breakdown occurs for a semiconductor at a particular value of field which is independent of amount of doping concentration.
Hence, breakdown field is same for both cases.
Now using, $E=\frac{dV}{dR},$we have
$\frac{V_{1}}{d_{1}}=\frac{V_{2}}{d_{2}}$
$\Rightarrow \frac{100}{20} =\frac{V_{2}}{1}$
$\Rightarrow V_{2}=5\,V $