(4) Which of the following cannot form a near-ohmic contact? ( )
(A) p-n junction
(B) n-n+ junction
(C) p-p+ junction
(D) Semiconductor-metal junction
A. p-n junction
Option A (p-n junction) is the correct answer
What is ohmic contact?
When a metal is connected to semiconductor material , it creates a junction called ohmic contact.
It is a low resistance junction in which current conduction takes place from metal to semi conductor and semiconductor to metal in both ways.
By heavily doping p and n layer p+ and n+ layers formed respectively .
p+ and n+ layers are itself much conducting so when p+ and p combinedp- p+ junction formed which is similar to metal to semiconductor combination.
In the same manner n- n+ junction too,
So p-p+ and n-n+ junction are ohmic contacts
And semiconductor to metal junction is ohmic contact.
p-n junction have barrier potential it cannot form ohmic contact.
Therefore option( A) p-n junction cannot form ohmic contact
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