Terahertz generation in submicron GaN diodes within the limited space-charge accumulation regime J. Appl. Phys. 98, 064507 (2005); 10.1063/1.2060956 Monte Carlo study of hot-carrier transport in bulk wurtzite GaN and modeling of a near-terahertz impact avalanche transit time diode J. Appl. Phys. 95, 7925 (2004); 10.1063/1.1702144 Monte Carlo analysis of GaN-based Gunn oscillators for microwave power generation J. Appl. Phys. 93, 4836 (2003); 10.1063/1.1562734 Monte Carlo calculation of electron initiated impact ionization in bulk zinc-blende and wurtzite GaNThe conditions for microwave power generation at low temperatures under optical phonon emission are analyzed by Monte Carlo simulations of both small-and large-signal responses in bulk zinc blende and wurtzite GaN. As a result of the high optical phonon energy and the strong interaction of electrons with optical phonons in GaN a general improvement on the transit-time resonance and a considerable increase in the maximum generation frequency and power can be achieved in comparison to the widely studied III-V materials such as GaAs and InP. A dynamic negative differential mobility caused by transit-time resonance occurs in a wide frequency range of about 0.05-3 THz and persists in the THz frequency range up to the liquid nitrogen temperature with doping levels up to about 5ϫ10 16 cm Ϫ3 . The efficiency of the amplification and generation is found to depend nonmonotonously on static and microwave electric field amplitudes, generation frequency, and doping level so that for each generation frequency there exists an optimal range of parameter values. Under optimal conditions a generation efficiency of about 1% to 2% can be achieved in the 0.5-1.5 THz frequency range.

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We present a hydrodynamic model to simulate the excitation by optical beating of plasma waves in nanometric field effect transistors. The biasing conditions are whatever possible from Ohmic to saturation conditions. The model provides a direct calculation of the time-dependent voltage response of the transistors, which can be separated into an average and a harmonic component. These quantities are interpreted by generalizing the concepts of plasma transit time and wave increment to the case of nonuniform channels. The possibilities to tune and to optimize the plasma resonance at room temperature by varying the drain voltage are demonstrated.

We report on systematic measurements of resonant plasma waves oscillations in several gate-length InGaAs high electron mobility transistors (HEMTs) and compare them with numerical results from a specially developed model. A great concern of experiments has been to ensure that HEMTs were not subject to any spurious electronic oscillation that may interfere with the desired plasma-wave spectroscopy excited via a terahertz optical beating. The influence of geometrical HEMTs parameters as well as biasing conditions is then explored extensively owing to many different devices. Plasma resonances up to the terahertz are observed. A numerical approach, based on hydrodynamic equations coupled to a pseudo-two-dimensional Poisson solver, has been developed and is shown to render accurately from experiments. Using a combination of experimental results and numerical simulations all at once, a comprehensive spectroscopy of plasma waves in HEMTs is provided with a deep insight into the physical processes that are involved.

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In the framework of analytical and hydrodynamic models for the description of carrier transport and noise in high electron mobility transistor/field-effect transistor channels the main features of the intrinsic noise of transistors are investigated under continuous branching of the current between channel and gate. It is shown that the current-noise and voltage-noise spectra at the transistor terminals contain an excess noise related to thermal excitation of plasma wave modes in the dielectric layer between the channel and gate. It is found that the set of modes of excited plasma waves can be governed by the external embedding circuits, thus violating a universal description of noise in terms of Norton and Thevenin noise generators.

A Monte Carlo particle (MCP) bipolar model for 4H-SiC consisting of three electron and two hole bands is developed to simulate the millimetre wave power generation by 4H-SiC IMPATT diodes. Validation of the model is provided by comparing (i) carrier transport properties with full band simulation results and (ii) hole impact ionization coefficients with the most recent experimental results. MCP simulation results are reported for a low-voltage 4H-SiC IMPATT diode connected directly in a parallel resonant circuit with a standard 50 load resistor. The detailed evolution of carrier generation, accumulation and drift are presented to confirm the design of an efficient hi-lo IMPATT diode structure. Critical performance parameters investigated include bias and frequency dependences of millimetre wave output power, generation efficiency, conduction current and frequency stability at an operating frequency around 200 GHz. It is predicted that very high-power millimetre waves at around 200 GHz can be generated at pulse mode.