When introducing the polarization effect of ALGAN/GAN structure in modellling of HEMT in silvaco atlas, i have confusion with how the values of the parameters polar.scale and piezo.scale are specified. I found different works using different value and could not find the reason. As i check it has a huge impact in threshold voltage but not much significant changes in the polarization charge or 2deg concentration. Please help me.
THANK YOU
Hi Terirama,
I think polar.scale and piezo.scale control the same quantity, that is the charge on upper and lower interfaces of a strained region.
You can specify polar.scale on the region statement like this:
region modify name=buffer polarization calc.strain polar.scale=0.8
When you adjust polar.scale you should see the values change in the table shown in the runtime:
Region Spontaneous Piezoelectric Total
Number Polarization Polarization Polarization
Sheet Charge Sheet Charge Sheet Charge
per sqcm per sqcm per sqcm
-------------------------------------------------------
1 1.0e+13 4.0e+11 1.04e+13
.......
Changing polar.scale will have a strong effect on the threshold voltage as you have found. Usually polar.scale can be used a fitting parameter to make your simulation agree with measurements. However if you are just using simulation I would suggest a value in the range 0.7 to 0.9 would be typical for GaN HEMT.
Alex
Thank you very much Alex. I used 0.8 and the result seems ok but it takes sheet charge density cause by piezoelectric as 0 all the time for me regardless of the value. Anyways thank you very much for the idea.
use interface charge at AlGaN/GaN interface. like below
"interface charge=1e13 y.min=.52 y.max=.52 s.s "
this interface charge is better than polarization model. First your requirement is how much 2deg you want?. Then, You can adjust the interface charge (1e13) to get the required 2deg. The ymin=0.52 is the AlGaN/GaN interface. This kind of interface charge will not create the convergence issue much. The convergence issue is more in polarization model.
if you take polar.scale=x,
The Net polarization=x*(Total polarization)
Regards,
Dhanu Chettri
- Badges
- Science topic
- Similar topics
- Philosophy
- Philosophy Of Science
- Reasoning