I am performing a simulation of AlGaN/GaN HEMT.

as many papers reported, the mobility of the 2DEG is very high, almost 2000, however, in the bulk GaN, the mobility of electrons is relatively low, about smaller than 1000.

I find the mobility of 2DEG is lowest, about 1000 and the mobility of electrons in the bulk GaN maintains constant ,about 1200 under the situation of Source , Gate and Drain all biased with 0V in my simulation. This phenomenon obviously contradicts the truth.