How to change germanium absorption coefficient for photodetector FDTD simulation?


#1

Hi,

I am trying to learn the example below:

https://kb.lumerical.com/en/pic_photodetectors_sige_lpd.html

but i do not know how to change the absorption coefficient of the germanium material. As there is a sentence in the example: In the 3D optical simulation with FDTD Solutions, the absorption coefficient used for germanium was 5 times larger than typical values for bulk germanium. This accounts for the increase in absorption for high-temperature-growth Ge films compared to bulk Ge [Guoiliang2012].

I am wondering is there any way to change the absorption coefficient of the Ge? Does anyone know? I cannot find in the software.

Thanks.

Yiding


#2

The absorption coefficient of a material is proportional to the imaginary part of the refractive index. In this example, the germanium material used in the FDTD simulation is an (n,k) material where the value of k was set to be 0.02835.

If you look at the default germanium materials you will see that at the simulation wavelength (1.55 um) the value of k is about 0.0056, 5 times smaller than the value used in the example.