Learning Forum

[ssj]

Hi,

I obtained the absorption spectra of a semiconducting layer using (a) periodic boundary condition and (b) PML boundary condition and observed that it greatly differ in both the cases. The absorption under PML boundary condition is lesser that the case where periodic boundary condition is used. Can you please help me undestand why is it so? What does this physically mean? I understand that if a nanostructure is placed on top of the semiconducting layer, applying a periodic boundary condition will replicate a nanostructure array compared to a single nanostructure when PML is used, and hence the absorption in the semiconducting layer can be higher in the former. But how can we explain the difference in case of a bare semiconducting layer?

Thanks in advance!

[Guilin Sun]

They should be different, since when PML boundary conditions are used, it will truncate the plane wave, causing diffraction.

The correct way for the thin-film type ( layered as you said) is to use periodic BCs. This is becuase they are assumed infinitely long perpendicular to the thickness axis. They are also periodic in principle.