Mechanism of two-dimensional electron gas formation in AlxGa1−xN/GaN heterostructures

Mechanism on the formation of two-dimensional electron gas (2DEG) at the interface of undoped AlxGa1−xN with undoped GaN was interpreted through surface band bending observed using synchrotron radiation photoemission spectroscopy. The surface Fermi level was independent of AlxGa1−xN thickness and Al content in AlxGa1−xN, showing Fermi pinning to surface states at 1.6 eV below conduction band minimum. Oxygen donor impurities in undoped AlxGa1−xN, unintentionally doped during the growth, led to the formation of large density of 2DEG (>∼1013/cm3) at the AlxGa1−xN/GaN interface via electron generation.