As part of a project work I had to derive the absorption of a thin-film stack. It was a semiconductor between two oxides on a metallic back reflector. I used Fresnel equations and optimized the absorption by adjusting the thickness. After fabricating the device, it looked quite black, which was exactly what was the goal. Therefore my calculations seem to be successful and match the problem.
I am now putting everything in my thesis, but there is one open question for me. As a body that is absorbing is also emitting, I would expect the semiconductor material and back reflector to emit as well (as they have complex refractive indices). My question is, how the Fresnel equations could possibly already account for this problem (I don't think that they'll do)? Emission in my opinion can occur at any depth of the material, so if I would consider it, I would get all kinds of different phase shifts, intimating a very messy calculation. Nevertheless it seems, that emission is only a minor problem, because otherwise my structure would be far from being a good absober, thus far from being black. Any ideas, why that is the case?
Thanks for any help!