We report on the transport properties of a two-dimensional electron gas (2DEG) confined in an AlGaN∕GaN heterostructure grown by plasma-assisted molecular-beam epitaxy on a semi-insulating GaN template prepared by hydride vapor phase epitaxy with a threading dislocation density of ∼5×107cm−2. Using a gated Hall bar structure, the electron density (ne) is varied from 4.1to9.1×1011cm−2. At T=300mK, the 2DEG displays a maximum mobility of 167000cm2∕Vs at a sheet density of 9.1×1011cm−2, corresponding to a mean-free-path of ∼3μm. Shubnikov–de Haas oscillations, typically not observed at magnetic fields below 2T in GaN, commence at B=0.6T.

We report on the growth and transport properties of high-mobility two-dimensional electron gases (2DEGs) confined at the AlGaN/GaN interface grown by plasma-assisted molecular-beam epitaxy on GaN templates prepared by hydride vapor phase epitaxy. We have grown samples over a broad range of electron densities ranging from ns=6.9×1011 to 1.1×1013 cm−2, and at T=4.2 K, observe a peak mobility of 53 300 cm2/V s at a density of 2.8×1012 cm−2. Magnetotransport studies on these samples display exceptionally clean signatures of the quantum Hall effect. Our investigation of the dependence of 2DEG mobility on carrier concentration suggests that the low-temperature mobility in our AlGaN/GaN heterostructures is currently limited by the interplay between charged dislocation scattering and interface roughness.

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High and low temperature behavior of Ohmic contacts to AlGaN/GaN heterostructures with a thin GaN capWe study the transport properties of quantum point contacts in a GaN / AlGaN heterostructure. The conductance of our devices shows well-quantized plateaus, which spin-split in high perpendicular magnetic field. The g factor is 2.55, as derived from the point contact subband splitting versus perpendicular magnetic field. In addition to the well-resolved plateaus, we also observe evidence of "0.7 structure" which has been mainly investigated in the GaAs system.

We experimentally determine the density dependence of the transport lifetime (τt) obtained from low-field Hall measurements and the quantum lifetime (τq) derived from analysis of the amplitude of Shubnikov–de Haas oscillations in a tunable high mobility two-dimensional electron gas (2DEG) in a Al0.06Ga0.94N∕GaN heterostructure. Using an insulated gate structure, we are able to tune the 2DEG density from 2×1011 to 2×1012cm−2, and thus, monitor the evolution of the scattering times in a single sample at T=0.3K in a previously unexplored density regime. The transport lifetime τt is a strong function of electron density, increasing from ∼2.7ps at ne=2×1011cm−2 to ∼11ps at ne=1.75×1012cm−2. Conversely, we find that the quantum scattering time τq is relatively insensitive to changes in electron density over this range. The data suggest that dislocation scattering accounts for the density dependence of τq as well as τt in our low-density sample.