Learning Forum

[Mariah Ha]

Hi, 

I am simulating this photodiode structure in 3D using FDTD. I would like to use the stackrt command and validate the absorption through the analytic transfer matrix method that the stackrt uses.  I am following the "planar silicon solar cell example" which compares the A=1-R-T simulation result to the stackrt theoretical result. My question is, is the stackrt method valid for this particular structure? The stackrt takes only the thicknesses of the layers into consideration and does not take the lateral shape in the horizontal direction. I mean, it would give the same result for this structure and a similar structure where the silicon is a whole parallelipiped. When I compared simulation and theory I found a big difference that might be due to this fact. If the stackrt is not valid for my structure shape, does Lumerical include a similar method as stackrt that might take the shape of the structure into consideration when calculating the analytic transfer matrix method? 

Thank you. 

[Dimitris Polyzos]

Hello, 

thank you for contacting us.To get the same results from STACK solver and FDTD solver you should decrease the x boundaries of your FDTD solver. You can check the photo below to visualize what I mean. In this way both solvers will calculate the absorption/transmission and reflection with high accuracy and I reckon that their results would match.

 

STACK solver calculates R and T of a plane wave for a multi-layer formation using the analytic transfer matrix method. It doesn't recognize the lateral shape of the multilayered design. For this design I would suggest to use FDTD solver that simulates any abstract design. 

I hope I helped. Please let me know if you need further assistance.

Kind regards

Dimitris

[Mariah Ha]

Hi, thank you for the answer.  I am using only the FDTD solver. I am not using STACK solver. In FDTD, I am using the reflection and transmission monitors to calculate absorption as A=1-R-T (in the script) and using another method in the script based on the STACKRT command. So if I understood you, the STACKRT command does not give a good result for my structure , is that right? 

[Dimitris Polyzos]

Hello Mariah, 

The stackrt is recommended for multilayered structure. That being said, it will calcualte absorption and transmission for structures where are infinite in lateral y and y irentations. The same results will be returned for FDTD if your structure will have the same periodic structure. Please refer to this link for FDTD/STACK comparison: STACK-FDTD.

In your design it is better to use FDTD solver as you want to calculate transmission and absorption of a complex structure (stepped). I wouldn't say that the results returned from stackrt are not good, more likely different I reckon.

Thanks a lot in advance

Regards

Dimitris