- #1
Lambduh
- 69
- 1
Hi guys i have a question about how semiconductor materials absorb photons at less than the band gap energy. Particularly in an indirect material like silicon.
Looking at absorption spectra for silicon i expected for it to immediately drop off at lower than the band gap energy ~1100 nm (1.12 eV) but it definitely does not from the graphs that I've seen. Is this something to do with phonon assisted absorption (even then there doesn't seem to be enough energy, or momentum, to get absorbed? It just seems to me that for any photon with energy less than the bandgap the material should be transparent. Is this due to "traps" or some defects in the material? Thanks!
Mark
Looking at absorption spectra for silicon i expected for it to immediately drop off at lower than the band gap energy ~1100 nm (1.12 eV) but it definitely does not from the graphs that I've seen. Is this something to do with phonon assisted absorption (even then there doesn't seem to be enough energy, or momentum, to get absorbed? It just seems to me that for any photon with energy less than the bandgap the material should be transparent. Is this due to "traps" or some defects in the material? Thanks!
Mark