When we chose materials to form contact with silicon,sucn as metal, TCO or some other semiconductors, which parameter is choiced for the band alignment. So far I know that when metal comes into contact with silicon, we choose the work function for band alignment. However, for other materials, like TMOs(including WO3，V2O5 and MoO3), They also apply workfunction to achieve band alignment, why not select heterojunction theory to draw the band alignment, for TMOs are semiconductors. Yesterday, my senior brother first used the work function to draw the energy band alignment, and then he couldn't explain it, so he used the heterojunction to align the energy band, and then he kept consistent with his experimental results. So I'm confused
Dear Deca
There are distinguished energy for the different materials. For all materials there energy levels are aligned to the vacuum level Evac which is the free electron level with zero kinetic energy outside the material. In the netal the highest occupied energy level at zero Kelvin is the Fermi level Ef. Accordingly one define thw work function of the material phi = Evac-Ef, that the energy required to free one electron from the fermi level to the vacuum level.
In semiconductors there are the valence energy level Ev, the conduction band level Ec and the vacuum level Evac as a reference level. There is also the Fermi level Ef
Then one has the energy gap Eg= Ec-Ev,
Also one has the work function of the material as phi= Evac-Ef
The electron affinity X= Evac- Ec,
So when we bring a metal and a semiconductor into contact the Fermi level will be flat at thermal equilibrium. As a consequence band bending will formed and potential barriers will appear. These potential barrier control the flow of carriers between the two materials.
There are semiconductors which behave as metal like such as the normally conducting oxides such as SnO2 and ZnO. These materials are intrinsically n-type with high carrier concentration having ferni levels inside the conduction band like metals. And therefore one align then energetically as metals. If they have controlled semiconductor properties then they may be treated as semiconductors. In fact they must be treated as heavily doped semiconductors.
Representing them as metal may be a simplification.
Best wishes
