Electron mobility in very low density GaN∕AlGaN∕GaN heterostructures

We report on the transport properties of a tunable two-dimensional electron gas (2DEG) confined at the lower interface of a GaN∕Al0.06Ga0.94N∕GaN heterostructure grown by plasma-assisted molecular beam epitaxy on semi-insulating GaN templates prepared by hydride vapor phase epitaxy. Using an insulated gate Hall bar structure, the electron density is continuously tuned from ∼2×1012 down to 1.5×1011cm−2. At T=300mK, the 2DEG displays a maximum mobility of 80 000cm2∕Vs at a sheet density of 1.75×1012cm−2. At low densities, the mobility exhibits a power law dependence on density −μ∼neα, with α∼1.0, over the range of 2×1011–1×1012cm−2. In this density regime, the mobility is no longer limited by alloy scattering and long-range Coulomb scattering dominates. We discuss the dominant scattering mechanisms that presently limit low temperature mobility at electron densities below 1×1012cm−2.