Defect Evolution in 4H-SiC Sublimation Epi-Layers Grown on LPE Buffers with Reduced Micropipe Density
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Defect Evolution in 4H-SiC Sublimation Epi-Layers Grown on LPE Buffers with Reduced Micropipe Density R. Yakimova, M. Syväjärvi, H. Jacobsson, A. Kakanakova-Georgieva, T. Tuomi1, S. Rendakova2, V. Dmitriev2 and E. Janzén Department of Physics and Measurement Technology, Linköping University, SE-581 83 Linköping, Sweden 1 Optoelectronics Laboratory, Helsinki University of Technology, FIN-02150 Espoo, Finland 2 TDI, Inc.,Gaithersburg, MD 20877, U.S.A. ABSTRACT The objective of this work is to study defect occurrence and appearance in thick sublimation epitaxial layers grown on top of LPE layers with different thickness and substrates with reduced micropipe density. Data from growth on C-terminated surfaces are also presented. The results were analyzed with the aid of optical microscopy, SEM images, HRXRD and synchrotron white beam X-ray topography. A pronounced effect of the LPE (buffer) layer surface roughness on formation of dislocations and micropipes is observed in the sublimation epitaxy layers. While with increasing the thickness of the buffer layer the efficiency of the micropipe reduction increases, the structure quality of the top sublimation epilayer degrades. LPE layers with a thickness of 0.1 µm appear to be the best compromise. INTRODUCTION With the development of silicon carbide (SiC), III-Nitrides (e.g. GaN, AlN) and Diamond, modern electronics has entered the era of a new wide band gap semiconductor technology. Among these materials SiC is the most elaborated and thus the best candidate to replace the conventional semiconductors in hard electronics. It is expected that the energy saving systems and the environment will greatly benefit of using SiC based devices. The main advantage of SiC is the availability of substrates allowing homoepitaxial growth of layers and structures needed for fabrication of different devices. For example, 4H-SiC wafers are available up to 2-inch diameter on the market, in both low resistivity and semi-insulating forms. Homoepitaxial layers can be grown with high growth rate to a thickness of over 100 µm [1,2]. One major limiting factor on the way of SiC commercialization is the presence of grown-in extended defects such as screw dislocations and micropipes that are known to affect device performance [3,4]. Screw dislocations in epitaxial layers are normally inherited from the substrates. After Frank theory [5] micropipes are generally considered as empty-core screw dislocations with large strain energy (large Burgers vector), although the presence of edge components can not be ruled out [6]. Micropipes primarily follow the growth direction (c-axis) in SiC boules and substrates, and easily propagate into subsequently deposited epitaxial layers. We have shown [7,8] that micropipes in 6H and 4H SiC can be filled up during liquid phase epitaxial (LPE) growth and the mechanism of the filling process has been elucidated. Recently, it has been reported [9] that micropipes can be transformed to elementary screw dislocations at the early stage of CVD growth. Most probably such an effe
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