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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.

Decay of nonequilibrium longitudinal optical ͑LO͒ phonons is investigated at room temperature in two-dimensional electron gas channels confined in nearly lattice-matched InAlN/AlN/GaN structures. A nonmonotonous dependence of the LO-phonon lifetime on the supplied electric power is reported for the first time and explained in terms of plasmon-LO-phonon resonance tuned by applied bias at a fixed sheet density ͑8 ϫ 10 12 cm −2 ͒. The shortest lifetime of 30Ϯ 15 fs is found at the power of 20Ϯ 10 nW/ electron.

The experimental dependence of microwave noise temperature on supplied electric power is used to study hot phonons in an InP-based modulationdoped In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As/In 0.7 Ga 0.3 As/In 0.52 Al 0.48 As heterostructure with a two-dimensional electron gas channel (n 2D = 2.3 × 10 12 cm −2 ). The effective hot-phonon temperature is extracted for two-subband and six-subband models treated in the electron-temperature approximation. The estimated value for the hot-phonon lifetime with respect to the longitudinal optical phonon conversion into other vibration modes is (0.9 ± 0.3) ps at room temperature.

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Advantages and drawbacks of InN‐containing GaN‐based heterostructure field‐effect transistors (HFETs) are reviewed. The main attention is paid to fundamental processes and experimental observations associated with hot‐electron transport in two‐dimensional electron gas (2DEG) channels subjected to high electric fields. Complementary information is obtained from fluctuations. When interface roughness and alloy scattering are minimized, an important transport limitation originates from additional scattering of hot electrons by non‐equilibrium longitudinal optical (LO) phonons (hot phonons) governed by the hot‐phonon temperature and the hot‐phonon decay into acoustic phonons. The ultrafast decay is observed for high supplied power where the hot‐phonon lifetime of ∼60 fs is found. The optimal 2DEG density for the fastest decay of hot phonons is estimated and associated with LO‐phonon–plasmon resonance. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

online colour at: www.pss-a.com) Drain current degradation (stars [8]) correlates with hot-phonon lifetime (curve).