Search

A numerical study of a model photoconductor under pulse and continuous-wave laser excitation is presented. From the solution of a system of partial differential equations related to the populations of conduction and valence bands we analyze the time behavior of the photoexcited concentrations of electrons and holes where the diffusion phenomena and the presence of electric field are neglected. Additionally, for the three-level model, the population of traps level is also introduced and analyzed as a third variable. The dynamics of electrons, holes and traps levels concentrations are studied in the presence of different types of pulse and harmonic laser photoexcitations. We show that an improved physical insight is obtained through a systematic analysis of the influence of the main physical parameters, such as generation and recombination rates, between the available energy levels.

We present a theoretical investigation of high-frequency electronic noise in field-effect transistors used as detectors of TeraHertz radiation. Calculations are performed using the hydrodynamic-Langevin approach and specialized to the case of InGaAs high-electron mobility transistors. The main physical phenomena associated with the effect of branching of the total current between channel and gate and the appearance of two-dimensional plasma waves are discussed. We demonstrate that thermally excited standing plasma waves originate series of resonant peaks in the corresponding noise spectral densities whose presence can be controlled by the embedding circuit. A significant damping of the high-frequency excess noise is found when the transistor is submitted to a two-lasers optical photo-excitation presenting a beating frequency in the TeraHertz range. Finally, we discuss the dependence of the damping effect, as well as a shift of the resonance peaks from the presence of channel ungated regions.

International audience; We extend the iterative matrix method for the solution of the Boltzmann transport equation in multi-band semiconductors to the calculation of second order parameters such as correlation functions and the noise temperature. The method allows also the extraction of the diffusion coefficient in each valley. The results for the case of GaAs with two valleys show that the diffusion in this material is dominated mainly by interactions in the Γ valley. The calculated noise temperature is in good agreement with Monte Carlo results

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.

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.

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.