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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 5×1016 cm−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 exist...

We present a new numerical method to calculate the correlation functions in semiconductor materials by a direct solution of the Boltzmann equation. The correlation function is calculated solving a set of time-dependent Boltzmann equations corresponding to different initial conditions. As application, we present the calculation of the correlation function of velocity fluctuations and the noise temperature for holes in silicon at T=300 K. The results are in good agreement with Monte Carlo calculation as well as with experimental data.

A closed hydrodynamic model and the associated numerical procedures are developed for simulating hot‐carrier transport in submicron semiconductor devices. To check the validity of the model, the steady‐state characteristics of near‐micron n+nn+ InP diodes are compared with a standard Monte Carlo approach. The excellent agreement found fully validates the physical reliability of our model which has been further developed to investigate linear and nonlinear time‐dependent characteristics. The contribution of each part of the device, when operating as microwave power‐generation, is analyzed through the spatial profiles of the impedance‐field spectrum. The usual subdivision of the n‐region into a passive (dead‐zone) and active zone is carried out. The dead zone is found to manifest itself as a purely real resistance which is practically independent of the frequency. One or more spatial zones which are responsible for the generation are shown to be formed in the active region of the diode. By reducing the leng...

Analytical expressions are presented for the spectral density of current fluctuations derived from a rigorous theoretical analysis which can be applied at any electric‐field strength. The main peculiarities of these spectra are discussed from an analytical point of view and in terms of the physical processes involved at increasing electric fields. Then, two different expressions are provided for an analytical fitting of spectra based on physical parameters related to a rigorous eigenvalue expansion of the correlation functions. These model spectra are in good agreement with the experiments and the results of Monte Carlo simulations for the case of p‐type Si at 77 K.

We present a hydrodynamic-Langevin scheme to describe electronic noise in unipolar structures and evaluate the cross-correlation functions of conduction current fluctuations entering the transfer impedance method. The theory is developed in terms of microscopic fluctuations of carrier velocity and energy taking place during scattering events. Applications to submicron n+nn+ GaAs structures show that the contribution of stochastic velocity rate prevails over that of the energy rate in determining the cross-correlation function of conduction current fluctuations.

The voltage noise spectrum associated with velocity fluctuations is calculated for submicron n +nn+ GaAs structures in the framework of a closed hydrodynamic approach based on the velocity and energy conservation equations. Transit‐time effects are found to substantially influence the noise spectrum in a wide frequency range. The good agreement found with Monte Carlo simulations validates the proposed theoretical approach. We predict a minimum noise measure at the frequency of 250 GHz for the considered structure.

We present an original method to investigate electronic noise in semiconductor structures by providing a spatial analysis of the spectral density of voltage fluctuations under constant‐current conditions. Monte Carlo simulations performed for submicron n+nn+ structures of Si and GaAs show that at equilibrium most of the low‐frequency noise originates from the n‐region while at increasing voltages relevant contributions come from the hot electrons which penetrate the drain region.

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.

We present a theoretical investigation on the electrical behavior of submicrometer n+nn+ diode microwave generators. To this end we adopt a mixed scheme which uses space‐homogeneous and stationary Monte Carlo simulations to provide the input parameters for a hydrodynamic analysis of the diode performances. Comparison between GaAs and InP made devices working at 400 K give similar results by predicting generation frequencies up to 700 GHz for an active region length of 0.2 μm.

We report on measurements of radiation transmission in the 0.220–0.325 THz frequency range through GaN quantum wells grown on sapphire substrates at nitrogen and room temperatures. Significant enhancement of the transmitted beam intensity with applied voltage is found at nitrogen temperature. This effect is explained by changes in the mobility of two-dimensional electrons under electric bias. We have clarified which physical mechanism modifies the electron mobility and we suggest that the effect of voltage-controlled sub-terahertz transmission can be used for the development of electro-optic modulators operating in the sub-THz frequency range.

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 existin...

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.

By numerical simulations we investigate the dispersion of the plasma frequency in a n-type In0.53Ga0.47As layer of thickness W and submicron length at T=300K. For W=100nm and carrier concentrations of 1016–1018cm−3 the results are in good agreement with the standard three-dimensional (3D) expression of the plasma frequency. For W⩽10nm the results exhibit a plasma frequency that depends on L, thus implying that the oscillation mode is dispersive. The corresponding frequency values are in good agreement with the two-dimensional (2D) expression of the plasma frequency obtained for a ballistic regime within the in-plane approximation for the electric field. A region of cross over between the 2D and 3D behaviors of the plasma frequency is evidenced for W>10nm.