Question

When a p-n junction is reverse-biased, the current becomes almost constant at 25 μA. When it is forward-biased at 200 mV, a current of 75 μA is obtained. Find the magnitude of diffusion current when the diode is

(a) unbiased, (b) reverse-biased at 200 mV and (c) forward-biased at 200 mV.

Answer 1

i₁ = 25 μA, V = 200 mV, i₂ = 75 μA

a) When in unbiased condition drift current = diffusion current

 Diffusion current = 25 μA.

b) On reverse biasing the diffusion current becomes ‘O’.

c) On forward biasing the actual current be x.

x – Drift current = Forward biasing current

=> x – 25 μA = 75 μA

=> x = (75 + 25) μA = 100 μA.