A Monte Carlo study of hot-electron intrinsic noise in a n-type GaAs bulk driven by one or two mixed cyclostationary electric fields is presented. The noise properties are investigated by computing the spectral density of velocity fluctuations. An analysis of the noise features as a function of the amplitudes and frequencies of two applied fields is presented. Numerical results show that it is possible to reduce the intrinsic noise. The best conditions to realize this effect are discussed.

This paper reports the results of Monte Carlo simulations of electronic noise in a GaAs bulk driven by two mixed high-frequency large-amplitude periodic electric fields. Under these conditions, the system response shows some peculiarities in the noise performance, such as a resonant-like enhancement of the spectra near the two frequencies of the applied fields. The relations among the frequency response and the velocity fluctuations as a function of intensities and frequencies of the sub-terahertz mixed excitation fields have been investigated.1 Introduction The sensitivity of semiconductor based devices is strongly affected by the presence of noise, which sets the lower limit for signal detection in electronic circuits. Much effort has been devoted to achieve a physical understanding of microscopic noise mechanisms within solid-state electron devices and to model electronic noise under small-signal conditions. However, when real materials and devices are used at very high frequencies around the THz region (broadband services, mobile network, oscillators, mixers, etc), they exhibit strong nonlinearities, such as the appearance of hysteresis cycle in their characteristics and the generation of harmonics. High-order harmonic generation and frequency mixing effects have been investigated in low-doped bulk semiconductors subject to far-infrared intense electric field [1,2]. These studies have shown that, under wave-mixing signal regime an enhancement of the harmonic generation can be produced. This fact can be useful for possible applications of semiconductor devices as sources of THz radiation. Nevertheless, the extraction of these harmonics is limited by the intrinsic high-frequency noise of the nonlinear medium, which can mask the generated high-order harmonics. Therefore, under cyclostationary conditions, these dynamical effects have to be considered and nonlinear analysis of noise must be performed. Previous studies have analysed the electronic noise under large-signal conditions for the case of bulk semiconductor and simple devices [3][4][5][6]. However, to our knowledge, the noise behaviour in semiconductor systems has not been investigated in the presence of a mixing of coherent electromagnetic radiations of commensurate frequencies. The complex nonlinear phenomena involved in the wave mixing regime make essential an accurate simulation and analysis of the noise performance in semiconductor materials. The paper is organised as follows: in Sect. 2 a brief description of the model used in the many-valleys anisotropic Monte Carlo code and the theoretical approach used for fluctuations estimation are presented; in Sect. 3 the main results of calculations are reported and discussed and final conclusions are given in Sect. 4.

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The results of a Monte Carlo analysis of hotelectron intrinsic noise in a n-type GaAs bulk driven by two mixed large-amplitude alternating electric fields having frequency in the subterahertz range are presented. The noise properties are investigated by studying the velocity autocorrelation function and the noise spectrum. We explored the relations among the frequency response and the velocity fluctuations as a function of the frequencies and intensities of the mixed fields. When the semiconductor is driven by two mixed ciclostationary electric fields, a resonant-like enhancement of the spectra near the two frequencies of the applied fields is found.

We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron–hole pairs as well as for the carrier transport in moderate electric fields. The semiconductor behaviour is described by substituting the traditional statistical approach (requiring a deep mathematical background) with microscopic models, based on the Monte Carlo method, in which simple rules applied to microscopic particles and quasi-particles determine the macroscopic properties. We compare measurements of electric properties of matter with ‘virtual experiments’ built by using some models where the physical concepts can be presented at different formalization levels.

A Monte Carlo study of the role of the frequency on the hot-electron intrinsic noise reduction in an n-type GaAs bulk driven by two mixed cyclostationary electric fields is presented. Previous numerical results showed the possibility to reduce the diffusion noise under specific wave-mixing conditions. In this work the variations of the noise properties are investigated by computing and integrating the spectral density of the velocity fluctuations. We found that the effect of reduction of the noise level due to the addition of a second field at twice frequency is almost independent of the frequency.

An application of the Monte Carlo method to the diffusion of neutrons passing through a slab of a moderating material is presented. This method can be used as a tool to improve the student's comprehension of the statistical properties of many particle systems, showing the necessity of simulation procedures to obtain information on the expected results of real experiments. We have chosen a very simple example to illustrate it: the evaluation of the transmission, reflection and absorption probabilities of a monochromatic beam of neutrons diffusing through a slab of a moderator material. After a collision with a nucleus of the moderator the neutron may be either elastically scattered or captured. The transmission, reflection and absorption properties of the neutrons diffused by different moderating materials are visualized with the help of an appropriate animation program.

By using a multiparticles Monte Carlo technique, with a self-consistently coupled one-dimensional Poisson solver, we investigate the dependence of the nonlinear carrier dynamics in GaAs n + nn + micro e submicro-structures operating under very intense sub-terahertz signals by: (i) the frequency and the intensity of the excitation signal and (ii) the length of the n region.