On the Role of Foreign Atoms in the Optimization of 3C-SiC/Si Heterointerfaces
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*Groupe d'Etude des Semiconducteurs, CNRS, UMR 5650, Universitd Montpellier 2, cc074, Place E. Bataillon, 34095 Montpellier cedex, France, masri(&intl.univ-montp2.fr **TU Ilmenau, Institut fuir Festk6rperelektronik, PSF 100565, 98684 Ilmenau, Germany ABSTRACT 3C-SiC/Si structures with Ge incorporation are elaborated by solid source molecular beam epitaxy (SSMBE). A comparison of the flatness of the SiC-surface and the interface between SiC and Si by comparing the deposition with and without Ge is made. The results are analyzed within the framework of a theoretical approach based on the theory of elasticity. INTRODUCTON Silicon carbide has garnered a particular attention because it has been guessed as a promising material for high-temperature and high-power electronic devices. Sensors based on SiC are indeed aimed because of the high thermal, chemical and mechanical stability of this material. The elaboration of high quality epilayers, which can be used as an efficient active part of a device, is strongly dependent on substrate surface quality. Among others, two approaches of SiC film epitaxial growth are currently considered. The investigation of the state of art of SiC wafer elaboration shows that wafer surface crystalline quality suffers from the existence of extended defects as dislocations and micropipes. This really represents a serious disadvantage of homoepitaxial growth as these structural defects can have dramatic consequences on device performance, especially because of their replication in the grown SiC active layer. Another alternative is afforded by heteroepitaxial growth of SiC on Si substrates. The
reasons for using Si is that large area of Si wafers, cheaper than SiC wafers, can be elaborated with a high surface crystalline quality. However, when using this solution, an important problem, related to the lowering of residual stress, must be solved. This methodology presents indeed a disadvantage due to the large mismatches of lattice parameters and thermal expansion coefficient respectively equal to 20 % and 8 %. Because of these mismatches and beyond layer critical thickness, extended defects, like for instance dislocations, can be favored from the formation energy point of view. Moreover, because of lattice parameter differences separating SiC and Si, stresses can not be fully relaxed by the dislocation network introduced at the SiC/Si interface during the carbonization of Si-substrate surfaces. As extended defects play a vital role in the quality of the final product, it is then worth seeking for a methodology which enables to smooth out their differences. Among the different techniques which can smooth out the effect of large lattice mismatch, the buffer layer technique has been widely used to assist heteroepitaxial growth. The carbonization of clean Si surface using hydrocarbon radicals is generally performed at the early stage of the growth process. Gas source molecular beam epitaxy (GSMBE) experiments [1] have shown that when one uses (CH 3 )2 GeH 2 (DMGe) as carbon source, the morphology of
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