Hello,

You need to add the source of 2DEG. In AlGaN/GaN heterojunction, polarizations are the main source of 2deg.

You need to define materials making heterointerface and their properties. ,Mole concentration/ traps /polarization charges etc are used by models to calculate 2DEG at heterointerface.

2deg=polarization charge+surface donor

if neglect surface donor , there will be a large reduction in 2deg and drain current

See the results of example 15.3 in tonyplot. Take a vertical cutline at center of structure. In this cutline, plot electron concentration, you will get a graph of 2DEG vs. thickness. Integrating this value over a small thickness will give you 2DEG in cm-2.