Fig. 6
From: Impact of Surface States and Aluminum Mole Fraction on Surface Potential and 2DEG in AlGaN/GaN HEMTs
a, c Conduction band variation either side of the AlGaN–GaN interface for 5% aluminum and b, d for 30% aluminum. Deep level surface trap does not contribute electron and positive sheet charge to the potential well and surface, making conduction band slope higher. Even for deep donor surface state (1.4 eV) there is 2DEG potential well is forming for 30% aluminum. This is not true for 5% aluminum