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Etude femtoseconde de la relaxation des électrons dans les semiconducteurs en régime non-markovien

Abstract : This work deals with the electron relaxation in semiconductors and, in particular, in gallium arsenide. The approach is experimental (femtosecond lasers) as well as theoretical (semiconductor Bloch equations and quantum kinetics). It provides new information on the fundamental processes, like carrier scattering, which cause a change of the electron energy and which are important for the functioning of electronic or optoelectronic devices. The study is based on the use of femtosecond lasers and on an original nondegenerate pump-probe technique : the pump pulse injects electrons and holes in a very short time, while the probe pulse is tuned to another higher-lying transition using the spin-orbit split-off valence band. This enables us to follow selectively with a 30-fs resolution the evolution of the electron distribution without superimposing the hole distribution to the signal. The very first instants of the electron relaxation were observed, during the injection, when the distribution is still completely out of equilibrium, until a thermalized distribution is reached (in less than 300 fs). The theoretical study shows the need of a non-markovian description of the processes. In order to take into account memory effects, quantum kinetics is used in the framework of the semiconductor Bloch equations. The Boltzmann equation and Fermi's golden rule are in fact not applicable in this case. The agreement between theory and experiment is all the more remarkable since no adjustable parameter was required. The influence of several parameters was also studied: a high carrier density slows down the relaxation, while the initial presence of cold carriers dramatically accelerates it. The initial excess energy seems on the other hand to be of less importance. The method has been also adapted to the study of the relaxation in quantum wells and the first results are presented.
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Submitted on : Tuesday, April 13, 2010 - 8:00:00 AM
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  • HAL Id : pastel-00005946, version 1



François-Xavier Camescasse. Etude femtoseconde de la relaxation des électrons dans les semiconducteurs en régime non-markovien. Physique [physics]. Ecole Polytechnique X, 1998. Français. ⟨pastel-00005946⟩



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