Characterization of SiC grown on Ge modified silicon substrates
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Characterization of SiC grown on Ge modified silicon substrates J. Pezoldt1, Th. Stauden1, Ch. Förster1, P. Masri2 1 TU Ilmenau, Institut für Festkörperelektronik, Postfach 100565, D-98684 Ilmenau, Germany 2 Universite de Montpellier, Groupe d‘Etude des Semiconducteurs, 12 Place Eugene Bataillon, 34095 Montepellier CEDEX 5, France ABSTRACT Silicon carbide layers were grown by solid source molecular beam epitaxy on silicon (111). Prior to the silicon carbide growth different amounts of germanium were predeposited on the silicon surface. Structural and morphological investigations with reflection high energy electron diffraction, x-ray diffraction, atomic force microscopy and spectroscopic ellipsometry revealed an improvement of the surface and interface properties for Ge coverages around and below 1 ML. The improved structural properties of the heterojunction lead to an amendment of the forward and reverse properties of the SiC/Si heterojunction.
INTRODUCTION The silicon carbide - silicon heteroepitaxial system has a wide range of different applications in sensors [1-5], optoelectronics [5-8] and electronics [9-12]. The overwhelming problem in this heteroepitaxial system is the high lattice and thermal lattice mismatch between SiC and Si leading to high residual stress and large lattice defect densities in the grown silicon carbide layers. Another critical issue is the silicon outdiffusion through the growing SiC layers. These phenomena lead to insufficient electrical properties of the grown SiC layer and the heterojunction. This difficulties can be softened by applying different methods of Si substrate modifications. The most common are: (1) SiC growth on SOI substrates [13], (2) SiC growth on porous or nanostructured Si [14, 15], (3) growth of SiC on modified Si substrates [16, 17]. Only the last method is applicable if the electrical properties of the heterojunction are of interest. In this paper we report on the influence of Ge deposition on Si(111) surfaces prior to the carbonization step on the properties of the grown SiC(111) by using solid source molecular beam epitaxy. Furthermore, it will be demonstrated that the method applied lead to an improved electrical behaviour of the SiC/Si(111) heterojunction.
EXPERIMENTAL DETAILS The SiC layers were grown by solid source molecular beam epitaxy on on-axis boron doped p-type (111) Si substrates. The wafers had a resistivity of 1 to 10 Ω⋅cm. The 300 nm thick SiC layers were grown on Si in an UMS 500 Balzers MBE system. The growth procedure was a variation of the method reported in [18] and consists of the following process steps: (1) hydrogen plasma cleaning in a Balzers PCCM Plasma Module without any wet cleaning steps [19,20], (2) annealing at 750°C for 1 h in the deposition chamber, (3) 0 to 4 ML Ge deposition on the (7x7)Si reconstructed Si surface at 325 °C by electron beam evaporation (ML with respect to the Si(111) surface), (4) deposition of C on a (7x7)-Si reconstructed Si surface at 325°C, (5) heating up the Si wafer to 660°C within 3 min, (6) gradually i
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