Seminário de Computação e Informação Quântica 

13/09/2005, 14:00 — 15:00 — Sala P4.35, Pavilhão de Matemática
Francesco Ciccarello, U Palermo

Hot electron noise in n-type GaAs in crossed electric and magnetic fields

In the last decades the Monte Carlo method (MC) has proved to be a powerful tool for the investigation of transport properties of charge carriers in semiconductors in high electric fields (typically of the order of kV/cm). In particular, MC simulations are useful for studying noise properties. These are relevant from the technologic point of view as well as for their ability to provide information on the physical behavior of “hot” carriers. However, up to now no effort was done (at least for bulk zinc-blend semiconductors) to perform this kind of study in the case of systems driven by crossed electric and magnetic fields. To this aim we consider bulk n-GaAs in the context of a three valleys model. $\Gamma$, L and X valleys are assumed spherical and nonparabolic. Electron scatterings due to ionized impurities, acoustic and polar optical phonons in each valley as well as intervalley transitions between the equivalent and nonequivalent valleys are accounted for. The time evolution of the electron wave-vector during free flights is treated by means of a local parabolic approximation of the dispersion law. Stochastic properties of electron transport are investigated by analyzing the electron velocity auto-correlation function and the spectral density of its fluctuations. These functions are shown to be significantly affected by the presence of the magnetic field. It is found that the spectrum of fluctuations exhibits interesting features such as signatures of nonparabolicity (implying a reduction of the expected cyclotron frequency) and nonlinearity (due to the different effective mass of valleys). For suitable electric field strengths, noise is lowered by the action of the magnetic field in a wide range of frequencies with a simultaneous decreasing of its total power.