Question

If the relative permittivity of a diode remains constant, its area is doubled and its doping concentration is quadrupled. What is its new diffusion capacitance, of originally it was CD?

(a) 4CD

(b) 2CD

(c) 3CD

(d) CD

I have been asked this question in homework.

Asked question is from Diffusion Capacitance in division Diode Circuit of Analog Circuits

Answer 1

The correct answer is (a) 4CD

For explanation I would say: CD = \(\frac{εA}{W}\) ∝ A.\(\sqrt{Doping}\)

CD‘ = \(\frac{ε2A}{W}\) ∝ 2A.2 2A.\(\sqrt{4Doping}\) = 4 CD

CD‘ = 4CD.