Monte Carlo simulation of 2D TASER

A possibility to develop the so called TASER (Terahertz-Amplification-by-the-Stimulated-Emission-of- Radiation) by using two-dimensional (2D) electron transport in quantum well (QW) structures is investigated by Monte Carlo simulation of the optical-phonon-emission assisted transit-time resonance (OPTTR) of 2D electrons in momentum space under the low lattice temperature. A considerable extension of the frequency region for THz radiation generation (upto 5 times) when going from 3D- to 2D-case is predicted.     

Monte Carlo simulation of Schottky diodes operating under terahertz cyclostationary conditions

We report Monte Carlo simulations of the current response and noise spectrum in heavily doped nanometric GaAs Schottky-barrier diodes (SBDs) operating under periodic large-signal conditions in the forward bias region. Due to the rather thin depletion region and heavy doping of these diodes, we find that the returning carrier resonance is shifted well above the terahertz region, so that the low-frequency noise plateau extends over the terahertz region. Here, frequency multiplication and mixing can take place at noise levels equal or below than that of full shot noise. We show that the signal-to-noise ratio of these SBDs is definitely superior to that of bulk semiconductors exploiting velocity-field nonlinearity.     

Terahertz Generation from Dynamic Free-Carrier Superlattice in n + nn + InN Structures

Electron transport in InN n ⁺ nn ⁺ diodes is investigated by the Monte Carlo Particle technique at temperatures below about 80 K, when optical phonon emission is the dominating scattering mechanism. It is shown that at constant bias, high enough to force strong electron optical phonon interaction but below the threshold value for intervalley transfer processes, the profiles of the relevant physical quantities exhibit a periodic spatial behaviour in the n-region, thus leading to the formation of a superlattice like structure. Such a structure is found to be responsible for microwave power generation in the THz frequency range.     

Pseudo-two-dimensional Poisson equation for the modeling of field-effect transistors

A modified Poisson equation able to take into account the influence of gates and a δ-doping in FETs and HEMTs is proposed. This equation can be solved self-consistently together with 1D transport equations along inhomogeneous transistor channels like those of the hydrodynamic or drift-diffusion approximations or with a Monte Carlo simulator used to describe carrier transport in n⁺nn⁺ structures.     

Monte Carlo Simulation of Electronic Noise in Semiconductor Materials and Devices Operating under Cyclostationary Conditions

To qualify the feasibility of standard semiconductor materials and Schottky-barrier diodes (SBDs) for THz high-order harmonics generation and extraction, the noise-to-signal ratio is calculated by the Monte Carlo method. Heavily doped GaAs SBDs are found to exhibit conditions for frequency mixing and harmonics extraction which are definitively superior to those of bulk materials.     

Free-carrier grating due to the optical phonon emission in InP n + nn + structures

Electron transport in 5 μm long InP n ⁺ nn ⁺ structure with the n-region doping of 10¹⁵cm⁻³ is theoretically investigated by the Monte Carlo Particle (MCP) technique at low lattice temperature (T = 10 K), when dominating scattering mechanism is the optical phonon emission. It is shown that at the constant bias a free-carrier grating (FCG) can be formed inside the n-region. The simple model of FCG formation is proposed and verified by MCP simulation of electron transport and noise in the considered InP structure.     

Monte Carlo simulation of threshold bandwidth for high-order harmonic extraction

The feasibility of bulk semiconductors subjected to strong periodic electric fields for terahertz radiation generation due to the high-order harmonic extraction is analyzed by using Monte Carlo simulations. The high-order harmonic intensity and the spectral density of velocity fluctuations are calculated for GaAs, InP, and InN. By comparing the harmonic intensity with the noise level the threshold bandwidth for high-order harmonic extraction determined by their ratio is introduced and evaluated for the above materials. The results show that semiconductor materials with a high value of the threshold field for the Gunn-effect are characterized by a high value of the threshold bandwidth under high-order harmonic generation and, hence, they are promising materials for microwave generation in the THz frequency range by high-order harmonic extraction.     

Numerical modeling of TeraHertz electronic devices

We investigate by means of Monte Carlo simulations the physical processes associated with the emission of TeraHertz radiation in different electronic devices. We analyze four alternative and complementary strategies which seem to be promising candidates to obtain the TeraHertz emission: (1) a nitride maser based on the optical-phonon transit-time resonance, (2) the high–order harmonic generation in bulk materials and nanometric Schottky-barrier diodes, (3) the excitation of coherent plasma oscillations in micron and submicron diodes, (4) the current instabilities and plasma oscillations in high electron mobility transistors (HEMT). The numerical results show that several physical mechanisms can be exploited to increase significantly the operating frequency of these devices and the best conditions to optimize the radiation emission in the TeraHertz range are studied in detail.     

Analytical model of high-frequency noise spectrum in Schottky-barrier diodes

We propose an analytical model for the high-frequency noise of Schottky-barrier diodes (SBD). The high-frequency spectrum is shown to be governed by collective motions of carriers in the neutral region of the SBD caused by the self-consistent electric field. The model is validated by comparison with Monte Carlo simulations of GaAs SBDs operating from barrier-limited to flatband conditions.