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We report the results of the Monte Carlo simulation of electron dynamics in stationary and space- and time-dependent electric fields in compensated GaN samples. We have determined the frequency and wavevector dependencies of the dynamic conductivity, σ ω , q (i.e., the electron response to high-frequency electrical signals). We have found that the spatially dependent dynamic conductivity of the drifting electrons can be negative under stationary electric fields of moderate amplitudes, 2..5 kV / cm. This effect is realized in a set of frequency windows. The low-frequency window with negative dynamic conductivity is due to the Cherenkov mechanism. For this case, the time-dependent field induces a "traveling wave" of the electron concentration in real space and a "standing wave" in the energy/momentum space. The higher frequency windows of negative dynamic conductivity are associated with the optical phonon transient time resonances. For this case, the time-dependent field is accompanied by oscillations of the electron distribution in the form of the "traveling" waves in both the real space and the energy/momentum space. We discuss the optimal conditions for the observation of these effects. We suggest that the studied negative dynamic conductivity can be used to amplify electromagnetic waves at the expense of energy of the stationary field and current. [ABSTRACT FROM AUTHOR]

The static and dynamic properties of hot electrons in nitride-based bulk semiconductors through Monte Carlo calculations of velocity-field characteristics, and of the spectra of differential mobility, velocity noise, and noise temperature is investigated. The results confirm that nitrides are promising materials for high-speed, high-power, electronic devices operating at room and higher temperatures.

A study was conducted to observe the terahertz emission from InGa/As/InAlAs lattice-matched high electron mobility transistors. The results showed that the emission appears in a threshold-like manner when the applied drain-to-source voltage U(sub DS) is larger than a threshold value U(sub TH).

A method is proposed for calculating the intrinsic noise of a semiconductor sample in the presence of high-order harmonic generation.

Low-temperature high-field electron transport is studied for compensated bulk GaN subjected to crossed electric and magnetic fields. The electron kinetics, distribution function, and field dependencies of the magneto transport characteristics are analyzed by using the Monte-Carlo method. At zero magnetic field, for an ionized impurity concentration of 1016 cm-3 and an electron concentration of 1015 cm-3, it is shown that dissipative streaming transport with a strong anisotropic electron distribution in the momentum space is realized at electric fields in the range 3 -- 10 kV/cm and for a lattice temperature of 30 K. The magnetic field destroys the dissipative streaming transport. Indeed, for a magnetic field greater than 4 T, the electrons are predominantly confined in a region of the momentum space where their energy is smaller than the optical phonon energy and the strong inelastic scattering by optical phonons is practically eliminated. A quasi-ballistic electron transport occurs in the form of a vortex-like motion in the momentum space. The axis of rotation of this vortex coincides with the average electron momentum. A general analysis of the distribution function suitable for any configuration of the Hall circuit is presented. The main magneto transport characteristics (dissipative current, Hall current, and Hall electric field) are studied for the short and open Hall circuits. We show that the magneto transport measurements can provide valuable information on the main features of the electron distribution function and electron dynamics in GaN. Finally, we suggest that the strong dependency of the dissipative current on the parameters of the Hall circuit can be used for current modulation and current switching. [ABSTRACT FROM AUTHOR]

We derive at first-order the carrier and velocity conservation equations and a pseudo-2D (P2D) Poisson equation in order to obtain an analytical model suitable for the study of the optical and electrical excitations of the plasma modes in a gated semiconductor channel of arbitrary thickness. We calculate the dispersion relation of the plasma waves appearing in the channel and the frequencies of the eigen modes for different boundary conditions (BCs). Then, we obtain and comment different THz-range frequency responses to an uniform optical beating or to an electrical excitation applied on the gate or the drain contacts. The effects of the different stimulations and boundary conditions are compared, and the responses, characterized by sharp resonances in the THz range, are interpreted as the sum of the contribution of the different hybrid plasma modes excited in the slab. [ABSTRACT FROM AUTHOR]

We have analyzed low-temperature behavior of two-dimensional electron gas in polar heterostructures subjected to a high electric field. When the optical phonon emission is the fastest relaxation process, we have found existence of collective wave-like excitations of the electrons. These wave-like excitations are periodic in time oscillations of the electrons in both real and momentum spaces. The excitation spectra are of multi-branch character with considerable spatial dispersion. There are one acoustic-type and a number of optical-type branches of the spectra. Their small damping is caused by quasi-elastic scattering of the electrons and formation of relevant space charge. Also there exist waves with zero frequency and finite spatial periods-the standing waves. The found excitations of the electron gas can be interpreted as synchronous in time and real space manifestation of well-known optical-phonon-transient-time-resonance. Estimates of parameters of the excitations for two polar heterostructures, GaN/AlGaN and ZnO/MgZnO, have shown that excitation frequencies are in THz-frequency range, while standing wave periods are in sub-micrometer region. [ABSTRACT FROM AUTHOR]

We report on photo-induced terahertz radiation with a high spectral purity generated by a submicron sized InGaAs-based high-electron-mobility transistor. The emission peak is due to the electron-hole pairs photocreated in the transistor channel at the frequency of the beating of two cw-laser sources. The radiation frequency corresponds to the lowest fundamental plasma mode in the gated region of the transistor channel. The observed high emission quality factor at 200 K is interpreted as a result of stream-plasma instability in the two-dimensional electron gas whose appearance is emphasized by the reduction of the velocity relaxation rate with the temperature. [ABSTRACT FROM AUTHOR]

We report a microscopic investigation of the spectrum of voltage fluctuations in nanometric n-Si layers. Theory makes use of a Monte Carlo simulator self-consistently coupled with a two-dimensional Poisson solver. We consider layers of variable thickness W in the range of 2–100 nm and variable length L in the range of 10–1000 nm embedded in an external dielectric medium. Calculations are performed at T=300 K for different doping levels and in the presence of an applied voltage of increasing strength. The spectra are found to exhibit peaks centered on the terahertz region. For W≥100 nm and carrier densities of 5×1017 and 5×1018 cm-3, the frequency peaks agree with the value of the three dimensional plasma frequency. For W≤100 nm, the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency covers a wide range of values of 0.2–10 THz and is in agreement with the values of the two-dimensional plasma frequency predicted by existing analytical models. At sufficiently high voltages, the two-dimensional plasma peak is washed out and we observe the onset of a peak in the subterahertz region which is associated with transit time instabilities induced by current saturation conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 UDS is larger than a threshold value UTH. The spectrum of the emitted signal consists of two maxima. The spectral position of the lower-frequency maximum (around 1 THz) is sensitive to UDS and UGS, while that of the higher frequency one (around 5 THz) 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. [ABSTRACT FROM AUTHOR]

The 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 5x10[sup 16] cm[sup -3]. 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. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a theoretical model for the noise properties of n[sup +]nn[sup +] diodes in the drift-diffusion framework. Incorporation of both the drift and diffusive parts of the current under inhomogeneous and hot-carrier conditions; Characterization of the noise properties of the diodes.

We have presented the results of terahertz time-domain spectroscopy measurements and a rigorous electrodynamic modeling of the optical characteristics of grating-based AlGaN/GaN plasmonic structures with low-doped two-dimensional electron gas in the frequency range of 0.1...1.5 THz. Two samples with grating aspect ratios (strip width/period) of 2.4/3 and 1.2/1.5 μm have been investigated. The measured transmission spectra are reconstructed in the calculations with high accuracy. The transmission spectra for p-polarized incident radiation exhibits Fabri–Pérot oscillation behavior due to the optically-thick substrate. The specific values of amplitude and spectral position of the transmission maxima are associated with the coupling of terahertz radiation with 2D electron gas due to plasmon excitations. Both calculations and transmission/reflection measurements demonstrate that plasmonic structures with micro-scaled metallic grating have three-fold increase of non-resonant absorption of terahertz radiation in comparison with the bare heterostructure. The polarization measurements of the transmission spectra of the plasmonic structures well agree with calculations and indicate a well-pronounced filtering effect of the grating for the s-component of the incident electromagnetic wave. The obtained values of the transmission for p- and s-polarized incident radiation demonstrate the high quality of deposited metallic grating with the extinction ratio higher than 80:1 for sub- and few THz frequency range. [ABSTRACT FROM AUTHOR]

Focuses on a study which analyzed the noise temperature associated with velocity fluctuations during non-linear transport in semiconductors. Theoretical model; Results; Conclusions.

Presents a study which derived an analytical theory of the hyperfrequency differential-mobility for nonlinear transport in semiconductors. Methods in the analysis of differential mobility; Description of the theoretical model; Results for holes in silicon.

Presents a study which reported a theoretical investigation and experiments on the conductivity of lightly doped p-silicon. Theoretical model used; Materials and methods used; Description of the ohmic conductivity as a function of the acceptor concentration.