Terahertz emission from InGaAs/ InAlAs lattice-matched high electron mobility transistors was observed. The emission appears in a threshold-like manner when the applied drain-to-source voltage U DS is larger than a threshold value U TH. The spectrum of the emitted signal consists of two maxima. The spectral position of the lower-frequency maximum ͑around 1 THz͒ is sensitive to U DS and U GS , while that of the higher frequency one ͑around 5 THz͒ is not. The lower-frequency maximum is interpreted as resulting from the Dyakonov-Shur instability of the gated two-dimensional electron fluid, while the higher frequency is supposed to result from current-driven plasma instability in the ungated part of the channel. The experimental results are confirmed by and discussed within Monte Carlo calculations of the high-frequency current noise spectra.

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By using a semi-classical two-dimensional (2-D) Monte Carlo simulation, simple ballistic devices based on AlInAs/InGaAs channels are analyzed. Our simulations qualitatively reproduce the experimental results in T-and Y-branch junctions as well as in a ballistic rectifier appearing as a result of electron ballistic transport. We show that a quantum description of electron transport is not essential for the physical explanation of these results since phase coherence plays no significant role. On the contrary, its origin can be purely classical: the presence of classical electron transport and space charge inside the structures.

By using arrays of nanowires with intentionally broken symmetry, we were able to detect microwaves up to 110 GHz at room temperature. This is, to the best of our knowledge, the highest speed that has been demonstrated in different types of novel electronic nanostructures to date. Our experiments showed a rather stable detection sensitivity over a broad frequency range from 100 MHz to 110 GHz. The novel working principle enabled the nanowires to detect microwaves efficiently without a dc bias. In principle, the need for only one high-resolution lithography step and the planar architecture allow an arbitrary number of nanowires to be made by folding a linear array as many times as required over a large area, for example, a whole wafer. Our experiment on 18 parallel nanowires showed a sensitivity of approximately 75 mV dc output/mW of nominal input power of the 110 GHz signal, even though only about 0.4% of the rf power was effectively applied to the structure because of an impedance mismatch. Because this array of nanowires operates simultaneously, low detection noise was achieved, allowing us to detect -25 dBm 110 GHz microwaves at zero bias with a standard setup.

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The static and dynamic behavior of InAlAs/InGaAs double-gate high-electron mobility transistors (DG-HEMTs) is studied by means of an ensemble 2-D Monte Carlo simulator. The model allows us to satisfactorily reproduce the experimental performance of this novel device and to go deeply into its physical behavior. A complete comparison between DG and similar standard HEMTs has been performed, and devices with different gate lengths have been analyzed in order to check the attenuation of short-channel effects expected in the DG-structures. We have confirmed that, for very small gate lengths, short-channel effects are less significant in the DG-HEMTs, leading to a better intrinsic dynamic performance. Moreover, the higher values of the transconductance over drain conductance ratio g m /g d and, especially, the lower gate resistance R g also provide a significant improvement of the extrinsic f max. Index Terms-Double-gate high-electron mobility transistor (DG-HEMT), dynamic behavior, Monte Carlo (MC) simulations.

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