Time transient generation rate



I want to calculate the generation rate in FDTD but in “time-transient” and then import the this generation rate to DEVICE for transient simulation. Is this possible?



Hi Mostafa. My apologies for the late reply (just had a long weekend). Before answering the question, may I ask what you like to simulate with this transient generation rate? Usually, the response time for the electrical system is so large compared to the optical period that you can consider any changes in the optical system (turning on and off) instantaneous from the electrical point of view. This allows us to use the steady-state solution from the optical simulation (generation rate in /cm^3/sec) and use an optical shutter to turn the generation rate ON or OFF in a transient electrical simulation to calculate the response time. You can find such an example here in the KB: Vertical Photodetector.


Hi Aalam,

Many thanks for your response.

Actually I want to shine just one “optical pulse” with 50fs width to the vertical photodetector. This pulse generates electron and holes in Ge and then I want to find out that what the generated current in DEVICE is (versus time with constant voltage in electrodes).



Hi Mostafa,

Thanks for the feedback. If you are interested in looking at the response of the system to a single pulse then you should be able to use the above mentioned approach and use the “pulse-on” option in the shutter in (transient) CHARGE solver to calculate the time resolved generation current for your device (see screenshot below). However, one issue that I can see is that the pulse width of 50 fs is too small for the electrical solver. The transient solver in DEVICE can give you accurate results for time steps down to 1 ps ~ 500 fs which means that the minimum allowed pulse width is about 10 times larger than what you have. Is it your intention to get the impulse response of the photodetector by applying the 50 fs pulse? If that is what you want then note that in the above mentioned example (Vertical Photodetector) we have shown how you can get the impulse response by taking the derivative of the step response of the VPD.