Question

a. Explain what is meant by the barrier potential and how it is formed before any bias is applied. [3 marks] b. When the diode is forward biased: i. What happens to the barrier potential? [1 mark] ii. What happens to the depletion region? [1 mark] iii. Indicate on your diagram the directions in which the holes and electrons move. [2 marks] c. Explain what is meant by the forward voltage drop of a diode. [2 marks] d. When the diode is reverse biased: i. What happens to the depletion region? [1 mark] ii. What causes the reverse bias leakage current? [2 marks]

Answer 1

(a) The potential barrier is the barrier in which the charge requires additional force for crossing the region.

How It gets established --

(b) after forward biase

after biasing-

(c)

When any device conducting in forward bias then practically there is a voltage drop across the device is called as forward voltage drop of that device.

Ideally this forward voltage drop assumed to be zero but practically very small voltage drop is there. for eg. 0.7V for Si.

(d)

It is seen that in a reverse-biased diode, some current flows through the depletion region. This current is called leakage current. Leakage current is dependent on minority current carriers. As we know that the minority carriers are electrons in the P type material and holes in the N type material.