Intrinsically limited mobility of the two-dimensional electron gas in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures

We report on the intrinsically limited low-field mobility of the two-dimensional electron gas (2DEG) in gated AlGaN/GaN and AlGaN/AlN/GaN heterostructures. Monte Carlo transport simulations are carried out to calculate the room-temperature 2DEG mobilities in dependence on the electron sheet density. The simulated 2DEG mobilities are compared to the phonon-limited mobility of bulk GaN. We estimate a maximum 2DEG mobility of about 2700 cm2 V−1 s−1 for an electron sheet density of ∼5×1012 cm−2, which remarkably exceeds the phonon-limited bulk mobility of 1520 cm2 V−1 s−1. By reducing the electron sheet density below 5×1012 cm−2, i.e., in a weak electron quantum confinement regime, the room-temperature 2DEG mobility gradually decreases and approaches the phonon-limited bulk value for vanishing quantum confinement. The insertion of a thin AlN barrier interlayer improves transport properties of the 2DEG and the mobility substantially increases due to a suppression of the alloy scattering.