Thu February 21, 2013 By:

why barrier height is reduced in forward biasing and it is increased while reverse biased please explain

Expert Reply
Fri February 22, 2013

Suppose a voltage V is applied, so thatn-side is negative and p-side is positive. The applied voltage V is opposite to the junction barrier potential. This leads to the barrier potential becomingand hence the energy barrier across the junction decreases. More majority carriers are now allowed to flow across the junction, and the junction width decreases. Since the bias polarity assists flow of current due to majority carriers, this configuration is called the 'forward bias configuration'. The current flow is due to majority carriers, and is large, of the order of milli Amperes. 
Behaviour under Reverse Bias: In this configuration, the voltage on the n-side is positive and that on the p-side is negative. This increases the junction potential to. As a result, the junction width will increase. The higher junction potential restricts the flow of majority carriers to a much larger extent. However, this will assist the flow of minority carriers, so the reverse bias current will be due to minority carriers only. Since the number of minority carriers is very small, this current will be of order.

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