Why is the absorption depth for GaAs more than for Germanium?

[A Sofyan]

It is based on the value of the edge coefficient I obtained, for Germanium at the wavelength of 1550 nm has a value of 459.54 / cm and GaAs at wavelength 885.6 nm has a value of 239.78 / cm.

If based on the theory of absorption depth (1 / alpha), then the optimal thickness of GaAs is thicker than Ge, and to my knowledge, this seems to be wrong in the application, can anyone explain? Is there something wrong with my understanding?

 

[Charles Link]

Both materials, if I'm not mistaken, are in a transition from being opaque at shorter wavelengths to starting to become transmissive at 1550 nm. Is there any reason you think Ge should be more transmissive than GaAs at this particular wavelength?

 

[A Sofyan]

Both materials, if I'm not mistaken, are in a transition from being opaque at shorter wavelengths to starting to become transmissive at 1550 nm. Is there any reason you think Ge should be more transmissive than GaAs at this particular wavelength?

It is based on the value of the edge coefficient I obtained, for Germanium at the wavelength of 1550 nm has a value of 459.54 / cm and GaAs at wavelength 885.6 nm has a value of 239.78 / cm.