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Microwave noise technique is applied to study energy dissipation in an AlN/GaN heterostructure containing a two-dimensional electron gas channel. Measurements of the dissipated power and the noise temperature are performed at 80 K lattice temperature in the electric field range up to 40 kV/cm. The energy relaxation time is found to decrease from 40 ps to 0.55 ps when the bias is increased. The experimental data are discussed in the electron temperature approximation assuming electron energy dissipation on optical phonons and hot-phonon effects. Dependencies of the hot-phonon number and the hot-phonon temperature on the hot-electron temperature are deduced. The frequency cutoff imposed by the limited energy dissipation through optical phonons is estimated.

Additional friction due to Pauli constraint, channel self-heating, alloy scattering, and hot phonons is reconsidered.

Hot-electron fluctuation techniques were developed for experimental investigation of picosecond and subpicosecond electronic and phononic processes in voltage-biased 2DEG channels of interest for microwave low-noise and high-power transistors. Examples illustrate real-space transfer, hot-electron energy relaxation, and occupancy relaxation of hot-phonon modes. The pioneering results on hot-electron energy relaxation and hot-phonon lifetime are confirmed by time-resolved response experiments. The fluctuation technique for measuring the hot-phonon lifetime as a function of the hot-phonon temperature is unique, no datum has been reported for comparison as yet.

The transverse runaway (TR) is a phenomenon whereby for a certain combination of energy and momentum scattering mechanisms of hot electrons, and for a certain threshold of the applied electric field, the internal (total) field tends to infinity. In this work, the effect of the magnetic field on the transverse runaway threshold is considered. It is shown that with increasing magnetic field, the applied critical electric fields relevant to TR decrease.

The obtained results are important for practical applications of the TR effect as well as for the investigation of possible nonlinear oscillations that may occur near the TR threshold.

A model calculation is given for the energy relaxation of a nonequilibrium distribution of hot electrons prepared in a metallic sample that has been subjected to homogeneous photo-excitation by a femtosecond laser pulse. The model assumes that the photoexcitation creates two interpenetrating electronic subsystems, initially comprising of a dilute energy-wise higher-lying nondegenerate hot electron subsystem, and a relatively dense, lower-lying electron subsystem which is degenerate. The relaxation process is taken to be dominated by the electron–(multi)phonon interaction, resulting in a quasi-continuous electron energy loss to the lattice bath. A novel physical feature of the kinetics considered here is the slowing down of the electron–phonon relaxation in the vicinity of the Fermi energy of the degenerate subsystem, due to the fermionic blocking of the interaction phase space. This leads to a peaking of the calculated hot electron distribution at the Fermi energy. This feature, as well as the entire evolution of the hot electron distribution, may be time-resolved by a pump-probe study. The model is particularly applicable to disordered metallic systems with low electron concentrations and strong electron–phonon coupling, and that are at high temperatures, where the usual two-temperature model^1–3 may not be appropriate.

We examine the impact of the hot drifting electron on stimulated Raman backscattering, which is coupled to decay instability, in a magnetized plasma. Through parametric coupling, this produces a plasma wave that moves forward and an electromagnetic wave that shifts downward. The plasma wave produced by stimulated Raman scattering (SRS) in this process decays into an ion-acoustic wave and a secondary, longer-wavelength Langmuir wave traveling opposite to the ion-acoustic wave. This energy diversion and attenuation of the primary Langmuir wave by drifting electrons limit the amplitude of SRS. In the presence of drifting electrons, the SRS is suppressed significantly and the plasma wave is attenuated resonantly at a higher rate.

The paper overviews recent progress in the field of hot-electron microwave noise and fluctuations with an emphasis on contribution due to inter-electron collisions that are inevitable in doped semi-conductors at a relatively high density of mobile electrons. A special attention is paid to the problem of hot-electron diffusion in the range of electric fields where inter-electron collisions are important and Price's relation connecting diffusion and noise characteristics is not necessarily valid. The basic and up-to-date information is presented on methods and advances in the field where combined analytic and Monte Carlo methods of investigation are indispensable while seeking coherent understanding of experimental results.

Additional friction due to Pauli constraint, channel self-heating, alloy scattering, and hot phonons is reconsidered.

Microwave noise technique is applied to study energy dissipation in an AlN/GaN heterostructure containing a two-dimensional electron gas channel. Measurements of the dissipated power and the noise temperature are performed at 80 K lattice temperature in the electric field range up to 40 kV/cm. The energy relaxation time is found to decrease from 40 ps to 0.55 ps when the bias is increased. The experimental data are discussed in the electron temperature approximation assuming electron energy dissipation on optical phonons and hot-phonon effects. Dependencies of the hot-phonon number and the hot-phonon temperature on the hot-electron temperature are deduced. The frequency cutoff imposed by the limited energy dissipation through optical phonons is estimated.

Hot-electron fluctuation techniques were developed for experimental investigation of picosecond and subpicosecond electronic and phononic processes in voltage-biased 2DEG channels of interest for microwave low-noise and high-power transistors. Examples illustrate real-space transfer, hot-electron energy relaxation, and occupancy relaxation of hot-phonon modes. The pioneering results on hot-electron energy relaxation and hot-phonon lifetime are confirmed by time-resolved response experiments. The fluctuation technique for measuring the hot-phonon lifetime as a function of the hot-phonon temperature is unique, no datum has been reported for comparison as yet.