Why doesnt a positively ionized donor atom contribute to co

. Why doesn’t a positively ionized donor atom contribute to conduction in an n-type semiconductor?

Solution

Consider a silicon semiconductor. When a trivalent impurity is added to silicon, then it forms a different type of semiconductor named p-type semiconductor. Gallium is a trivalent impurity. If we add gallium to silicon, it forms a p-type semiconductor.

When a pentavalent impurity is added to silicon, then it forms an n-type semiconductor. Arsenic is a pentavalent impurity. If we add arsenic to silicon, it forms an n-type semiconductor.

In the case of n type semiconductor more number of free electrons are there, so, they only contribute to conduction.

positively inoised donors are not present in the n type semiconductors.