Explain the terms ‘depletion layer’ and ‘potential barrier’ in a p-n junction diode. How are the 
(a) width of depletion layer, and
(b) value of potential barrier affected when the p-n junction is forward biased ?

The small region in the vicinity of the junction which is depleted of free charge carrier and has only immobile ions is called depletion region/ layer.
The accumulation of negative charges in p - region and positive charges in n- region set up a potential difference across the junction, which acts as a barrier and is called barrier potential.
In forward bias (a) width of depletion layer decreases (b) value of potential decreases