Hot-electron noise is investigated for InGaAs and InAs quantum wells containing a two-dimensional electron gas channel in a pulsed electric field applied parallel to the interfaces. Noise sources resulting from hot-electron "thermal" motion, electron temperature fluctuations, and real-space transfer are observed. The experimental results on hot-electron "thermal" noise are used to estimate energy relaxation time in the field range where other sources do not play any important role. Measurements of noise anisotropy in the plane of electron confinement are used to discuss real-space-transfer noise. High-frequency noise technique is used to study hot-electron trapping, and trap location in InAlAs/InGaAs/InAlAs heterostructure channels is determined.
Experimental dependence of microwave noise temperature on supplied electric power is used to estimate hot-phonon number in a modulation-doped 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 two-dimensional electron gas channel (n_{2D}=2.3×10^{12} cm^{-2}). The nonequilibrium occupancy of the involved longitudinal optical phonon states exceeds the equilibrium one nearly twice at 2 kV/cm electric field.
The experimental results on transport, noise, and dissipation of electric power for voltage-biased Si-doped GaN channels are compared with those of Monte Carlo simulation. The measured dissipated power shows a stronger hot-phonon effect than the simulated one. On the other hand, the experimental results on the electron drift velocity at high electric fields show a weaker hot-phonon effect as compared with the simulated one. The misfit can be reduced if a conversion of the friction-active nonequilibrium longitudinal optical phonons into the friction-passive longitudinal optical phonons is considered.
Hot-electron transport and microwave noise are investigated for n-type 4H-SiC (n=2×10^{17} cm^{-3}) subjected to a pulsed electric field applied parallel to the basal plane. At room temperature, the negative differential conductance, masked by field ionization at the highest fields, is observed in the field range between 280 and 350 kV/cm. The threshold fields for the negative differential conductance and field ionization increase with lattice temperature. The results on microwave noise are used to evaluate the effective hot-electron temperature and the hot-electron energy relaxation time.
A study of the photoluminescence properties of AlInN/GaN in comparison with the spectrum of the GaN active layer of the same heterostructure is presented. The strong intensity lines of the observed photoluminescence spectra are associated with the formation, enhancement and narrowing of the excitonic lines in the flat band region of the active GaN layer. The phenomena in the presence of electric field near the heterostructure interface with the two-dimensional electron system are associated with nonlinear behaviour of recombination processes.
Microwave noise temperature, current, and dissipated power were investigated at room temperature in undoped AlGaN/AlN/GaN channels grown by molecular beam epitaxy and metal-organic compound vapour decomposition techniques. Samples with essentially the same electron density (1×10^{13} cm^{-2}) and low-field mobility (1150 cm^2/(V s)) demonstrated considerably different behaviour at high electric fields. The effective hot-phonon lifetime, 300 fs and 1000 fs, respectively, was estimated for molecular beam epitaxy and metal-organic compound vapour decomposition samples. The expected anti-correlation of hot-phonon lifetime and hot-electron drift velocity was confirmed experimentally.
Lifetime of non-equilibrium (hot) phonons in biased GaN heterostructures with two-dimensional electron gas channels was estimated from hot-electron fluctuations. Dependence of the lifetime on the electron density is not monotonous - the resonance-type fastest decay serves as a signature of hot phonons. The signature is resolved in nitride heterostructure field effect transistors when the gate voltage is used to change the channel electron density. The transistor cut-off frequency decreases on both sides of the resonance in agreement with the enhanced electron scattering caused by longer hot-phonon lifetimes. The signature is also noted in device reliability experiment: the enhanced temperature of hot phonons, possibly, triggers formation of new defects and accelerates device degradation.
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