Current–voltage characteristics of a nominally undoped AlGaN/GaN two-dimensional electron gas channel is measured at a room temperature, and electron drift velocity is deduced under assumption of uniform electric field and field-independent electron density. No velocity saturation is reached at fields up to 130 kV/cm, when the effect of Joule heating is minimized through application of nanosecond pulses of voltage. The estimated drift velocity is near 2×107 cm/s at 130 kV/cm. Monte Carlo simulation of the drift velocity is carried out with and without effects of channel self-heating for a many-subband model, with hot phonons and electron gas degeneracy taken into account.

The microwave noise technique is used to estimate the hot-electron energy relaxation time in an AlGaN/GaN heterostructure containing a two-dimensional electron gas subjected to a strong electric field applied in the plane of electron confinement. Room-temperature data show that the energy relaxation time decreases monotonously from about 1 ps at 2 kV cm −1 to 0.4 ps at 10 kV cm −1 electric field. The estimated low-field value is 1.4 ps.

Hot-electron transport was probed by nanosecond-pulsed measurements for a nominally undoped two-dimensional channel confined in a nearly lattice-matched Al 0.82 In 0.18 N / AlN/ GaN structure at room temperature. The electric field was applied parallel to the interface, the pulsed technique enabled minimization of Joule heating. No current saturation was reached at fields up to 180 kV/cm. The effect of the channel length on the current is considered. The electron drift velocity is deduced under the assumption of uniform electric field and field-independent electron density. The highest estimated drift velocity reaches ϳ3.2ϫ 10 7 cm/ s when the AlN spacer thickness is 1 nm. At high fields, a weak ͑if any͒ dependence of the drift velocity on the spacer thickness is found in the range from 1 to 2 nm. The measured drift velocity is low for heterostructures with thinner spacers ͑0.3 nm͒.

Nanosecond‐pulsed current–voltage measurements were used to study hot‐electron transport in undoped AlGaN/GaN and AlGaN/AlN/GaN two‐dimensional electron gas channels biased up to 200 kV/cm. Voltage pulses of 1 ns were applied in order to minimize channel heating. The current saturated at 100 kV/cm in the AlN‐interbarrier‐contained structures; the estimated saturated drift velocity was about 1.1 × 107 cm/s. No saturation of the current was observed in AlGaN/GaN channels in the field range below 200 kV/cm. Monte Carlo simulation of hot‐electron transport was carried out with electron gas degeneracy and hot phonons taken into account. A fairly good fit of the experimental results with the Monte Carlo simulation data was obtained in the electric field range up to 30 kV/cm. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The electron temperature method is developed for a high-density two-dimensional electron gas (2DEG). The relation of electronic noise and transport properties is obtained in the case of weakly inelastic scattering without considering the scattering mechanisms in detail. The method is applied to consider the experimental data on AlGaN/GaN 2DEG channels. The electron-temperature relaxation time and its dependence on electric field are extracted from the current–voltage and noise–voltage characteristics measured for two-terminal samples at 80 K. The method works in the field range up to 3 kV/cm in the considered 2DEG channels. In this range of fields, the electron temperature reaches 350 K, and the electron–temperature relaxation time diminishes from 5 ps at low fields to 0.4 ps at 3 kV/cm.