# Three dimensional vertical photodetector electrical device simulation stop at 98%

#1

vpd.ldev (6.6 MB)

I try to simulate the example in three dimension. https://kb.lumerical.com/en/pic_photodetectors_vertical_photodetector.html
I also include mobility model in Ge and I remove Auger and radiative recombination in Ge. But I failed to get the result, the process stop at 98% always.

By the way if I use the script command below, there will be an error.

setbc(“ncontact”,“geometry”,“Cathode:+x”);

And I have to click “edit contact” then choose the another “Cathode” to solve the problem. I would like to know how to create and set contact in the script language.

addbc(“electrical contact”,‘ncontact’);
setbc(“ncontact”,“geometry”,“Cathode:+x”);

Could you help me on this ?

#2

Hi @d01941013, I will look into your project file and try to figure out why your simulation is failing.

Regarding the “setbc” command, the electrical contact boundary condition is always applied to a geometry, not at the interface between a geometry and a solver boundary (which is what the Cathode:+x notation implies). The correct command for your electrical contact should be,

setbc("ncontact","geometry","Cathode:");

#3

Dear Sir,

I tried the command you suggested “setbc(“ncontact”,“geometry”,“Cathode:”);”

But I got the following message.

Error: prompt line 1: geometry ‘Cathode’ is not a valid choice”

There is Cathode in the structure. Can you help me with this?

Thank you very much.

Best regards,
Chun-Ti Lu

#4

Hi @d01941013, in my experience if you already have a boundary condition defined that is applied to the Cathode geometry then if you create another boundary condition and try to assign it to the Cathode geometry again then you will get such an error message. Try adding the command deleteallbc before adding the boundary conditions in your script to remove all pre-exisiting boundary conditions. My guess is that would solve this problem.

deleteallbc; addbc("electrical contact",'ncontact'); setbc("ncontact","geometry","Cathode:");

#5

I have taken a look at your file. First of all this is a very large 3D simulation so the memory requirement will be very large and the simulation time would be very long. Is there any reason why you want to perform the full 3D simulation? As shown in the KB example, a 2D simulation should give you the electrical properties of the photodetector.

Regarding your convergence problem, I believe this is coming from the fact that you have created the diffusion doping objects in such a way that they are ending at the edge of the metal contact (ans the Ge). Since the doping concentration of the diffusion doping object falls exponentially near the boundary, the doping under the metal contact does not remain constant throughout the length of the metal and this would make the simulation unstable.

If you extend the doping objects beyond the edge of the metal/Ge region then this problem should get fixed.

#6

A post was split to a new topic: Only one mesh constraint working out of two