Why MESFET is more linear than pHEMT?

When plotting the gm vs. Vgs, MESFET tends to have a wider flat area than pHEMT. From device physics perspective, why is that? Thanks.

Very good question! It probably involves lots of semiconductor physics. looking forward to good comments on this too.

http://www.csmantech.org/Digests/1999/PDF/42.pdf

I read this paper before, but where is the answer? Thanks.

Not much discussion on the linearity comparison in the paper...

"Broadband Microwave Amplifiers-Bal.S. Virdee,Avtar S. Virdee,Ben Y. Bentamin" Page 55-56

I read this book, I can't find the answer. Page 55-56 don't have the answer neither.

In the book, difference between Gm is discussed, but not the linearity. Nice try though.