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.