Learning Forum

[Mariah Ha]

Hi,

I am testing a simple 3D simulation in FDTD of a silicon block illuminated by a plane wave at 850nm. I am calculating the absorption of silicon using two methods. The first one is the method used in Lumerical example"Planar silicon solar cell" using the relation A=1-R-T where R and T are the reflection and the transmission obtained by monitors. I get around 37% absorption in this case. The second method is using the Pabs_total representing the total power absorbed per wavelength. I am applying for this a monitor (box ) encapsulating the silicon material. Here I obtain around 26% absorption only. Why does the second method give a different value? Does Pabs_total need additional calculations using scrpting? Isn't it direct ? If not, what does the 26% represent in my case?

Thank you.

 

 

[sagar]

The reflection monitor should be above the source. Another suggestion is to keep the PML at least lambda (wavelength) spacing from the top or bottom surface of the structure. The way you have placed the monitor for reflection is basically calculating the (source power - reflection), in the forward direction it is recording the actual injected power coming from the source and in the backwards direction it is calculating reflection and the result is giving as (source power - reflection), which you are thinking as reflection. 

Place the monitor before the plane wave source, you should get 55.5% reflection and 18.5% transmission.

 

[Mariah Ha]

Thank you for the reply and corrections. What about the Pabs_total method? Is it calculating the right absorption ? 

[Niki Papachristou]

Hi Maraih,

Thank you for reaching out to us! Let me refer you to this post: difference between Pabs_total calculated by analysis group

Kind Regards,

Niki

[Mariah Ha]

in the example "planar silicon solar cell", the reflection monitor is placed after the source. why?