Q3. Draw energy level diagram for an

a) unbiased p-n junction diode

b) forward biased p-n junction diode and explain how the barrier potential changes.

(a) Energy level diagram for unbiased p-n junction diode is as follows-

(b) Energy level diagram for forward biased p-n junction diode is as follows-

When the junction is unbiased, negative charge resides in p-side and positive charge resides in n-side. But when forward biased is applied, positive charge from p-side enters into n-side and negative charge from n-side enters into p-side. Thus, charge densities of both types reduce and hence, potential barrier reduces.