# Electron hole pairs, semiconductor theory

#### Michael Lake

Joined Oct 29, 2015
2
hi

im a first year mechactronics student and ive noticed one particular question that always come up the in the tests. ive googled for the answer and i get multiple different answers.

the question is as follows:
Electron hole pairs are made by...
a) doping b)thermal energy c) ionisation d) covalent bonding

this question originates from the semiconductor theory chapter in my course.
i think the answer is b

#### RBR1317

Joined Nov 13, 2010
631
That sounds like a trick question. I think I would rephrase the question to ask, The absence of what item in the list would mean there are no holes?

#### Michael Lake

Joined Oct 29, 2015
2
That sounds like a trick question. I think I would rephrase the question to ask, The absence of what item in the list would mean there are no holes?
ok so if its asked the way you put it what answer would you give?

#### Papabravo

Joined Feb 24, 2006
16,155
A brick of pure semiconductor has no electron-hole pairs regardless of the level of thermal energy. It is also true that the atoms in a brick of pure Silicon have covalent bonds to their neighbors in the crystal lattice.

#### RBR1317

Joined Nov 13, 2010
631
The most useful concept for explaining conduction in solids is the energy band model. In a semiconductor the electrons normally occupy the valence band but can jump to the conduction band if they absorb enough energy to overcome the band gap energy. When an electron jumps to the conduction band, it leaves behind a hole, thereby forming an electron-hole pair. Holes are the electron voids in the valence band. Thermal energy can cause an electron to jump the band gap but it is not the only source of energy capable of doing so. Note that this energy band model can apply to pure semiconductors. When applied to doped semiconductors, the explanation becomes somewhat more 'interesting'.