The first 3 marks of Q4 of the 2009 paper are about absorption in an n-doped silicon semiconductor. I'm not certain what the peaks in absorption it mentions correspond to.
We're at low temp, so I'm assuming we have carrier freeze-out. Then I'd have thought the series of peaks between 39 and 45 meV are excitations of electrons from the impurity band to the conduction band.
Then I'd have thought the very large increase at 3.3eV is excitation from the valence band to the conduction band.
Then I'm unsure on the step at 1.2eV - is that perhaps due to an indirect band gap?
I'm probably being very stupid, but if you could provide some clarification that would be great.