Finally Finished Some Simulation Runs
Well... it's taken me what... about 25 years?, but in the end, I finally finished the first 10 psec of the simulation that I started in my PhD, and was never able to finish. These are the two big results I was waiting for with the Gould NP1 but never managed to be able to get the results out of the box as it just took too bloody long. Well... fast forward to now, and I was able to run the simulations for all 10 psec on my iMac at home without any problem at all.
In fact, the total runtime for the entire 10 psec simulation was 4:34:54 - about four and a half hours! Had I told myself back then that someday I'd run this code on a desktop Mac and it'd finish in less than half a day, I'd have laughed. And then wondered when that day would come. How exciting!
The first test is the Si pulse. Here, we're looking for a nice, representative pulse widening and drifting down the channel. I was able to get a few psec of this simulation done for my thesis, and it proved that at least in Si, the physics was behaving as you'd expect.
The second test was the similar conditions in a GaAs channel where we're biased in the negative differential mobility zone, and so we'd expect the oscillations predicted by the 1D simulations to start to appear. What I'm seeing here isn't anything like that.
This pulse seems to be nearly stagnant in the channel - hardly drifting at all - but spreading out much faster than the Si device. While this might make sense, if you think of the higher mobility in GaAs over Si, the problem is, the mobility in the bias conditions we're looking at should be shrinking the packet and starting to make oscillations on the top part of the pulse.
So I'm wondering if I've got something wrong in the code, or if I just have it misconfigured. It sure looks like it's configured correctly. But then again, I don't have anything to compare it to. Hmmm... very odd.
Well, if I get more time I might dig into this, now that the runs can be done in a reasonable time. I just wonder if there's something I'm missing as the other tests all checked out. It's something to think about.