Question

In an unbiased $p - n$ junction, holes diffuse from the p- region because:
(A) Free electron in the $n$ -region attract them
(B) They move across the potential difference
(C) Hole concentration in $p$ -region is more as compared to n-region
(D) All of the above

Answer 1

Hint : First of all we have to study the properties of $p - n$ junction to answer this type of question. Properties of holes and electrons in $p - n$ junction will help us to find out the exact solution. These properties will tell us briefly about biasing and unbiasing of $p - n$ junction.

Complete Step By Step Answer:
Let us go through some important properties of $p - n$ junction.
When a small amount of pentavalent impurity is added to a pure semiconductor then this semiconductor is known as $n$ type semiconductor. Similarly, when a small amount of trivalent impurity is added to a pure semiconductor then this new form is called as $p$ type semiconductor.
When $p$ type semiconductor is joined perfectly with $n$ type semiconductor then this contact surface between them is known as $p - n$ junction.
$p$ -region contains holes i.e. positive charged particles and $n$ -region contains electrons which are negatively charged. The free electrons near the junction in the $n$ -region begin to diffuse across the junction into the $p$ -region and combine with holes near the junction. The result is that the $n$ region loses electrons as they diffuse into the junction.
There are two types of biasing in $p - n$ junction one is forward biasing and the other is reverse biasing. But here the condition is given that there is unbiased $p - n$ junction that means there is neither forward biasing and nor reverse biasing
Hence, we have reached the conclusion that holes in the $p$ region are attracted by the electrons in the $n$ region. The holes in $p$ region diffuse because holes concentration is more than that of electrons in $n$ region.
Thus, the correct option is A and C both.

Note :
The $n$ type semiconductor has pentavalent impurity e.g. Arsenic is the pentavalent impurity which provides electrons to the semiconductor crystal. And in $p$ trivalent impurity is added, trivalent is Gallium and is also known as acceptor impurity accepts electrons.