Two-dimensional electron gases induced by polarization charges in AlN/GaN heterostructure grown by plasma-assisted molecular-beam epitaxy

We discuss the growth and transport properties of two-dimensional electron gas confined at the AlN/GaN heterointerface grown by plasma-assisted molecular-beam epitaxy. The sheet carrier density was found to be highly dependent on the barrier thickness of AlN grown on a doped or undoped GaN layer. The carrier sheet density monotonously increased from 0.8x10(12) to 1.1x10(13) cm(-2) as the AlN barrier thickness on a semi-insulating GaN layer increased from 15 to 25 Angstrom due to spontaneous and piezoelectric polarization. An AlN barrier of 35 Angstrom in thickness grown on n-GaN gave the highest sheet carrier density, which was 4.3x10(13) cm(-2). In thin AlN barrier layers, the sheet carrier density was low due to surface depletion. (C) 2003 American Institute of Physics.