The absorption coefficient depends on the nature of the medium, the thickness of the membrane, and the absorption of the membrane material to the incident rays. So the smaller the thickness, the higher the absorption coefficient

The absorption coefficient depends on the nature of the medium, the thickness of the membrane, and the absorption of the membrane material to the incident rays. So the smaller the thickness, the higher the absorption coefficient

ميسم شهاب Does this changes with the microstructure of same material?

Hello Bibek,

the absorption coefficient changes definitely if structure and/or dimension change. This is due to the change of the density of states N(E) (E energy). Some examples:

- With decreasing thickness of a material the gap energy enhances. For a light beam near the (3-dim. ) gap energy Eg the absorption decreases abruptly, if Eg changes from hv > Eg to hv < Eg.

- The density of state in 3-dim. material has the form N(E) ~ E0,5 .

In 2-dim. material it is constant.

In wires it is E-0,5.

Therefore the absorption deceases systematically with

decreasing thickness.

- The absorption depends strongly from doping and real structure.

Generally, the whole optics is a science of absorption coefficient.

With regard,

R. Mitdank