Noise influence on electron dynamics in semiconductors driven by a periodic electric field

Studies about the constructive aspects of noise and fluctuations in different non-linear systems have shown that the addition of external noise to systems with an intrinsic noise may result in a less noisy response. Recently, the possibility to reduce the diffusion noise in semiconductor bulk materials by adding a random fluctuating contribution to the driving static electric field has been tested. The present work extends the previous theories by considering the noise-induced effects on the electron transport dynamics in low-doped n-type GaAs samples driven by a high-frequency periodic electric field (cyclostationary conditions). By means of Monte Carlo simulations, we calculate the changes in the spectral density of the electron velocity fluctuations caused by the addition of an external correlated noise source. The results reported in this paper confirm that, under specific conditions, the presence of a fluctuating component added to an oscillating electric field can reduce the total noise power. Furthermore, we find a nonlinear behaviour of the spectral density with the noise intensity. Our study reveals that, critically depending on the external noise correlation time, the dynamical response of electrons driven by a periodic electric field receives a benefit by the constructive interplay between the fluctuating field and the intrinsic noise of the system.Comment: 9 pages, 4 figures, to appear in J. Stat. Mechanics: Theory and Experim., 200

Analyse de la mobilité dans les transistors nanométriques

ISBN10 : 2-9527172-0-6International audienc

Analyse de la mobilité dans les transistors nanométriques

ISBN10 : 2-9527172-0-6International audienc

Model reduction of electric rotors subjected to PWM excitation for structural dynamics design

International audienceRotors of asynchronous machines can be subjected to risk of failure due to vibratory fatigue. This is caused by the way electric motors are powered. Pulse Width Modulation (PWM) is the control strategy of the traction chain. This signal is composed by a fundamental and numerous harmonics of voltage and current that induce harmonics onthe torquesignal resultingin hugetorque oscillations. It canlead to repeated torsionalresonance when coincidences occur. This can induce severe damages and even lead to rupture if electric excitations are not taken into account at the design stage. In this work, a magnetic finite element model is built by using Fourier decomposition in order to take into account harmonics due to PWM. Pressures exported from this model are used as inputs for mechanical FEM. A mechanical reduced order model is also proposed in order to compute stress in rotating part. This second model allows to reduce time computation and then to consider several operating points to build a complete speed up. A correlation is performed between these two models and rotating tests in order to discuss the relevance of these approaches to design rotor parts

Frequency limits of terahertz radiation generated by optical-phonon transit-time resonance in quantum wells and heterolayers

A universal description of the OPTTR-assisted generation band of THz radiation is developed in the framework of a 3D transport in bulk materials and 2D transport in QWs and HLs. On the one hand, in the framework of an ideal streaming motion we have carried out an analytical investigation based on phonon scattering rates: namely, elastic deformation acoustic phonons in the passive energy region below the optical-phonon energy 0 and emission of polar optical phonons in the active energy region, 0. On the another hand, quantitative estimations of the qualitative constraints given by Eqs. 1 and 2 for the streaming conditions are obtained on the basis of numerical calculations of the OPTTR DNDM by the Monte Carlo method. It is found that i for Eq. 1 the average momentum relaxation time in the passive region must satisfy the condition −1–2E and ii for Eq. 2 carrier penetration into the active region must occurr at a level less than 14%–15%. In the framework of such a model we have provided simple analytical expressions that estimate the low- and high-frequency limits of the generation band determined by, respectively, the average relaxation time − see Eq. 25 and the carrier penetration into the active region see Eq. 33. Having in mind that for THz radiation generation the high-frequency limit is of the most interest, for the highfrequency cutoff of the DNDM we have found that i for 3D bulk materials the relevant physical quantities are the carrier effective mass, the optical-phonon energy, and the polaroptical coupling strength; ii in passing from 3D to 2D vertical transport, for the same material the influence of 2D transport on the OPTTR is characterized entirely by the dimensionless parameter k0d related to both the radius of the optical-phonon sphere in wave-vector space k0 and the effective width of the electron localization d associated with the lowest miniband of the QW/HL structure; iii in going from 3D to 2D transport, the change of the energy dependence of the density of states is responsible for an extension of the maximum generation frequency for up to a factor of 5 times. In essence, such a model gives the “upper” estimation of the generation band limits determined primarily by the parameters of a bulk material and a 2D structure. Any other scatterings not incorporated directly into our model— namely, impurity, electron-electron, interface roughness, etc.—act mainly on the low-frequency limit since one can speak about the upper limit only in the case when an electron runaway from the regime of low-energy scatterings in the passive region takes place. Of course, the presence of additional low-energy scatterings will increase the low-frequency limit and eventually destroy the generation. Nevertheless, additional scattering mechanisms can be simply incorporated into the model by taking into account their contribution to the average momentum relaxation time in the passive region − as 1/−=1/DA+1/imp +1/ee. For example, such a procedure was used to estimate − in the experimental observation of the OPTTR generation in bulk InP.20 These estimations give relaxation times, which is reasonably close to the values estimated above

Terahertz generation in nitrides due to transit-time resonance assisted by optical phonon emission

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Terahertz generation in nitrides due to transit-time resonance assisted by optical phonon emission

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Is It Possible To Suppress Noise By Noise In Semiconductors?

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Monte Carlo calculation of diffusion coefficient, noise spectral density and noise temperature in HgCdTe

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