Thermal conductivity of regularly spaced amorphous/crystalline silicon superlattices. A molecular dynamics study
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Thermal conductivity of regularly spaced amorphous/crystalline silicon supe rlattices. A molecular dynamics study Konstantinos TERMENTZIDIS1,* , Arthur FRANCE-LANORD1 , Etienne BLANDRE1 , Tristan ALBARET2 , Samy MERABIA2 , Valentin JEAN 1 and David LACROIX1 1 Université de Lorraine, LEMTA, CNRS UMR 7563, BP 70239, Vandœuvre les Nancy cedex, France 2 Université de Lyon-1, ILM, CNRS UMR 5306, Bâtiment Kastler, 10 rue Ada Byron, 69622 Villeurbanne, France. *konstantinos.termentzidis@univ- lorraine.fr ABSTRACT The thermal transport in amorphous/crystalline silicon superlattices with means of molecular dynamics is presented in the current study. The procedure used to build such structures is discussed. Then, thermal conductivity of various samples is studied as a function of the periodicity of regular superlattices and of the applied temperature. Preliminarily results show that for regular amorphous/crystalline superlattices, the amorphous regions control the heat transfer within the structures. Secondly, in the studied cases thermal conductivity weakly varies with the temperature. This, points out the presence of a majority of non-propagating vibrational modes in such systems. INTRODUCTION The amorphous/crystalline superlattices (a/c SLs) with large conduction band discontinuities can be used for resonant-tunnelling diodes, modulation-doped field-effect transistors and quantum- well infrared photo-detectors1 . They are also interesting candidates for low-cost thermoelectric power devices2 . These SLs can be made of materials which display large lattice mismatch. Furthermore, they can have interfaces which are essentially defect- free and atomically sharp3 . To the best of our knowledge the only investigation of the heat transfer through a/c SLs interfaces was made by Von Alfthan4 et al. They conclude that the thermal conductivity of such superlattices is mainly ruled by the presence of amorphous regions, whatever are their sizes. We extend this study with the prediction of the Kapitza resistance and we study the effect of the SLs parameters such as period and temperature. A recent theoretical work of Donadio and Galli on crystalline silicon nanowires with amorphous surfaces showed that k is not affected by the temperature and it is close to the one of amorphous materials5 . This unusual temperature dependence is explained by the presence of a majority of non-propagating vibrational modes. There is a lack of information about a/c silicon interfaces, especially in what concerns both SLs and nanowires. In our study SLs of a-Si/c-Si preliminary results will present the thermal conductivity appraisal as a function of the SL’s periodicity. Then, the mean temperature of structures will be changed in order to assess k variations. Hereafter follows the simulation method description and the obtained results discussion. Eventually, conclusions and perspectives to this work are provided.
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SIMULATION METHOD In this study two molecular dynamics codes were used. The first one is a homemade molecular dynamics code, which is used t
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