about LDMOS current quasi-saturation

It's due to the carriers velocity saturation in the LDD region.Then which accounts for the quasi-saturation，high Vgs or high Vds?

high Vgs and low Vds

I am going to join a research group of Noise and Reliabilty in University of Texas at Arlington. I will start my work with LDMOS. Please suggest me some good study material, books on LDMOS basics.