Question

Problem #3: 3.6. A diode has wdo = 0.4 µm and φj = 0.85 V. (a) What reverse bias is required to triple the depletion-layer width? (b) What is the depletion region width if a reverse bias of 7 V is applied to the diode?

Answer 1

Answer:

a) 6.8 Volt

b) 1.21Цm

Explanation:

We are given from the question that

   The zero -bias depletion layer width($W_{do}$) is 0.4Цm

  The built in voltage φj  is 0.85V

Now to calculate the reverse voltage( $V_{R}$) that would be required  to triple the depletion - layer width.

  The depletion - layer width ($W_{d}$) of the diode has the formula

                          $W_{d} = W_{do} \sqrt{1 + \frac{V_{R} }{Qj} }$

    For three times of   $W_{d}$ we have

        $3W_{d} = W_{do} \sqrt{1 +\frac{V_{R} }{Qj} }$

         =>      $\frac{V_{R} }{Qj} = 3^{2} -1$

        => $V_{R} = 8Qj$

        Substituting value of φj

       We have

                         $V_{R} = 8(0.85V)$

                               =   6.8 V

The required bias voltage  $V_{R}$ is  6.8 V

   The solution for the b part of the question is uploaded on first image