How ionization energy can be lower than band gap?

[newuser]

I am reading about the ionization energy in semiconductors and came across this thing that for Silicon, the ionization energy is lower than its band gap energy. I don't understand how can this be?

 

[Matterwave]

Is this for the ionization energy of an electron in the conduction band? It seems to me that there should be no problem having an ionization energy lower than the band gap. Why do you find it problematic?

 

[newuser]

Well that makes sense. The book does not says it explicitly so I guess what you say is the case.

 

[rigetFrog]

I thought that was only the near the surface and when treated with a special coating. E.g. Ce on GaAs. I didn't think it was a bulk effect too. Are you reading a paper from before 1985? The history of semiconductors has a lot of back and forth.

 

[newuser]

@ rigetFrog: I was reading the book. The answer given by matterwave is correct. I has a silly confusion which is clear now.