Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors

The origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterost ructure field effect transistors is examined theoretically and experimental ly. Based on an analysis of the electrostatics, surface states are identifi ed as an important source of electrons. The role of the polarization-induce d dipole is also clarified. Experimental Hall data for nominally undoped Al 0.34Ga0.66N/GaN structures indicate that similar to 1.65 eV surface donors are the actual source of the electrons in the 2DEG, which forms only when t he barrier thickness exceeds 35 Angstrom. (C) 2000 American Institute of Ph ysics. [S0003-6951(00)01128-1].