The transport and quantum lifetimes were respectively deduced from low-temperature mobility and Shubnikov-de Haas measurements as a function of carrier density in metal organic vapor phase epitaxy-grown AlGaN/GaN/sapphire heterostructures. We show experimentally that the lifetime ratio varies as a bell curve, qualitatively confirming a recent theoretical prediction. However the experimental ratio varied much less than was theoretically predicted: From 9 to 19 for carrier densities in 1-9x10(12) cm(-2) range. Moreover, we show the variation of quantum time with carrier density presents some discrepancy with the theoretical study. We also show that transport to quantum lifetime ratio cannot be used alone as a clear figure of merit from AlGaN/GaN heterojunctions. (c) 2005 Americian Institute of Physics.

We report on the detection of the sub-THz and THz radiation by silicon FETs and on the voltage tunable emission of terahertz radiation from InGaAs/AlInAs HEMTs with nanoscale gate lengths. The observed photo-response is in agreement with the predictions of the plasma wave response theory. The spectrum of the emitted signal has two peaks. The lower peak is interpreted as resulting from the Dyakonov - Shur instability of the gated two dimensional electron fluid. The emission measurements in a magnetic field show that the threshold voltage remains close to the transistor saturation voltage that increases with magnetic field due to geometric magnetoresistance.

A resonant voltage tuneable radiation (0.4 THz-1.0 THz) from the gated two dimensional electron gas in a 60 nm InGaAs field effect transistor was investigated. We show that (i) the observed emission appears once the drain-to-source voltage, U-DS, exceeds the threshold value, U-TH; (ii) the resonant frequency can be tuned by U,,, in agreement with the current driven plasma instability model of Dyakonov and Shur; (iii) by applying a quantizing magnetic field one increases U-TH linearly with the magnetic field while the evolution of the emission signal is approximately a universal function of (U-DS - U-TH). (c) 2005 WILEY-VCH Verlag GmbH A Co. KGaA, Weinheim.

We report on the experiments about detection of the THz radiation by silicon FETs with nanometer gate lengths. The observed photo-responses measured as a function of the gate voltage are all in agreement with the predictions of the Dyakonov-Shur theory. The plasma wave parameters deduced from the experiments allow us to predict also the possibility of resonant detection in THz range by nanometer size silicon devices. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The influence of the magnetic field on the excitation of plasma waves in InGaAs/AlInAs lattice matched high electron mobility transistors is reported. The threshold source-drain voltage of the excitation of the terahertz emission shifts to higher values under a magnetic field increasing from 0 to 6 T. We show that the main change of the emission threshold in relatively low magnetic fields (smaller than approximately 4 T) is due to the magnetoresistance of the ungated parts of the channel. In higher magnetic fields, the effect of the magnetic field on the gated region of the device becomes important. (C) 2005 American Institute of Physics.