trouble with convergence in DEVICE with very high generation rate


#1

Hi,
I introduced a very high generation rate object into my DEVICE simulation of an unbiased waveguide. It is a transient simulation 5.5 ps long, with 0.5 ps minimum timesteps. The simulation runs fine when the generation rate object is disabled. However, I am having a lot of trouble getting the sim to converge with the generation rate object enabled. One thing I have tried is to introduce the generation rate object slower using the global shutter. I currently have the shutter opening at 0.5 ps, following a log slew function with t_slew = 5 ps. This seems to help with convergence at most timesteps but the simulation still fails to converge at the final timestep. I have also increased the mesh refinement sensitivity and the max refine steps. Doing so should help with convergence correct? Anyways, still no convergence. I would be very grateful if anyone is willing to take a look at my sim linked below and suggest anything else I can try to get convergence.

simulation file link

Best,
Patrick


#2

Hi @patrick.goley, I have looked at your file and the simulation seems to be working fine for me. If you are using an older version of DEVICE that I would recommend upgrading to the latest version first. The only thing I changed is the simulation end time (you would want it to be more that 5.5 ps if you want to observe the transient response of the photogenerated carriers). I did this by setting the last time step in the anode bias voltage to 20 ps (just for testing).

I also made the mesh much coarser to make the simulation faster:

The simulation ran without any error with these changes. I am attaching the modified file here: wg_absorption_ion_strike-1-21_MOD.ldev (6.1 MB) [I have deleted the import generation object to make the file smaller]

Please note that since you do not have any built in electric field (i.e. a PN junction) the current in the device will be quite small.
.


#3

Glad to know it wasn’t a problem with my simulation setup. I’ve since updated to the latest version of DEVICE and am also now running the program locally and on better hardware, whereas before I was running it remotely over a network (and on older hardware). Its now running smoothly. Thanks for the help!