High and low energy photon absorption

[Karim Habashy]

Hi All,

Kindly find here 2 questions, i was wondering about:

1) Will (helium cooled) Mono C-silicon be able to absorb a high intensity laser of about 900-1100 nm ?

2) How can Ultra-violet and visible light cause rise in material temperatures.

Thanks.

 

[Simon Bridge]

1. That would be IR so it would be surprising if some was not abdorbed.
2. Same way any light increases temperature.

 

[my2cts]

Silicon is quite transparent at photon energies below the indirect band gap of Eg=1.1 eV at room temperature.
It is an amazing experience to look straight trough a wafer with night vision.
There is absorption below Eg because the valence band is not fully occupied due to thermal effects.
Above Eg phonon assisted transitions occur.
At very low T it is the larger direct bandgap that determines absorption.
Anything at or below red light passes through.
See http://en.wikipedia.org/wiki/Direct_and_indirect_band_gaps#Implications_for_light_absorption
See also
http://refractiveindex.info/?shelf=main&book=Si&page=Vuye-20C