Question

Compared to p-n junction with N_A = N_D = 10¹⁴/cm³, which one of the following statements is TRUE for a p-n junction with N_A = N_D=10²⁰/cm³?
1. Reverse breakdown voltage is lower and depletion capacitance is lower
2. Reverse breakdown voltage is higher and depletion capacitance is lower
3. Reverse breakdown voltage is lower and depletion capacitance is higher
4. Reverse breakdown voltage is higher and depletion capacitance is higher

Answer 1

Correct Answer - Option 3 : Reverse breakdown voltage is lower and depletion capacitance is higher

Concept:

Depletion capacitance\(.{C_d} = A\sqrt {\frac{{q\epsilon{_s}}}{{2{V_{bi}}}}\frac{{{N_A}.{N_D}}}{{{N_A} + {N_D}}}} \),

\( =A \sqrt {\frac{{q\epsilon{_s}}}{{2{V_{bi}}}}\frac{N}{2}} \)  (Assuming N_A = N_D = N)

∴ C_d∝ N

And breakdown voltage decreases as doping increases.

So, the junction with N_A = N_D = 10²⁰ cm^-3 has, lower reverse breakdown voltage and higher depletion capacitance as compared to the one with NA = ND = 1014/cm3