What is an electron hole pair?

[anaqavi]

TL;DR Summary

Why are more electrons than holes in an n-type semiconductor?

Hi,

These questions may seem basic, yet, I do not have an answer for that.

The density of electrons and the density of holes in an intrinsic semiconductor are equal at equilibrium. From this, it seems that holes are simply lack of electrons that are given enough (thermal) energy to escape from a particular atom. Therefore, it is evident that the number of electrons and holes will be equal because for each electron that escapes from an atom an empty place -a hole- will be created.

However, when we consider a p-doped semiconductor, the number of holes will be much larger than the number of electrons. If a hole is simply lack of an electron, as in the previous case we should be able to conclude that the number of electrons and holes are equal. How to solve this contradictory reasoning?

Another question: Are pure Arsenide and pure Gallium assumed intrinsic?

 

[phyzguy]

In a pure semiconductor like silicon, you are right in that the number of electrons and holes will be equal. However, by doping the semiconductor, we can add electrons without adding holes, or holes without adding electrons. For example, in an N-type semconductor in the case of silicon, we dope the silicon by adding a group 5 element, which has 1 more valence electron. In this case the charge of the extra electron is compensated by the added charge in the nucleus of the group 5 doping element, not by an extra hole.

Pure gallium and pure arsenic are not semiconductors. Gallium is a metal, and arsenic is a semi-metal