Question

Consider two almost similar diodes, whose diffusion capacitances are C1 and C2, and doping concentrations of 1020 /cubic centimeter and 1016/cubic centimeter. Find \(\frac{C1}{C2}\).

(a) 100

(b) 0.01

(c) 10000

(d) 0.0001

This question was addressed to me in class test.

This interesting question is from Diffusion Capacitance topic in section Diode Circuit of Analog Circuits

Answer 1

The correct answer is (b) 0.01

Best explanation: C ∝ \(\frac{1}{\sqrt{Doping}}\)

\(\frac{C1}{C2} = \sqrt{\frac{10^{16}}{10^{20}}} = \sqrt{\frac{1}{10^4}} = \frac{1}{100}\)

\(\frac{C1}{C2}\) = 0.01.