Silicon Carbide Epitaxial Layers Grown on SiC Wafers with Reduced Micropipe Density
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RENDAKOVA" 2 , N. KUZNETSOV', 2N. SAVKINA', M.4 RASTEGAEVA', 1 ANDREEV , M. MINBAEVA', A. MOROZOV , and V. DMITRIEV "-' loffe Institute, St. Petersburg, 194021 Russia Crystal Growth Research Center, St. Petersburg, 194021, Russia MSRCE, Howard University, Washington, DC, 20059 USA TDI, Inc., Gaithersburg, MD, 20877 USA [email protected]
ABSTRACT The characteristics of SiC high-power devices are currently limited by the small area of the devices, which is usually less than 1 sq. mm. In order to increase device area, defect density in SiC epitaxial structures must be reduced. In this paper, we describe properties of silicon carbide epitaxial layers grown on 4H-SiC wafers with reduced micropipe density. These layers were grown by the vacuum sublimation method. Large area Schottky barriers (up to 8 mm 2 ) were fabricated on SiC epitaxial layers and characterized. INTRODUCTION High defect density in commercially available silicon carbide substrates is one of the main obstacles limiting the size of SiC devices [1]. As a result, the area of SiC devices usually does not exceed 1 mm 2 [2,3]. Forward current of bipolar SiC devices, being proportional to the device area, is less than 10 A at a voltage drop of 4 V [4]. In order to fabricate high-power SiC devices operating at currents of 100 A and higher, the device area must exceed 10 mm 2 . The defect is known to destroy any device if present in the device active area; this is the so-called micropipe defect [5] . Because of fundamental reasons for micropipe formation in SiC wafers [6], the problem of micropipes in bulk SiC material is not to be solved in the near future. These micropipes, originated from SiC substrates, penetrate in device structures during epitaxial growth and cause the device failure. In order to develop high-power large-area SiC devices, micropipes in SiC substrate materials must be completely eliminated. Recently, TDI, Inc. [7] have reported on the fabrication of silicon carbide epitaxial wafers with reduced micropipe density. In these wafers, micropipe channels are filled with silicon carbide, which is grown inside the channels. The best R&D wafers, both 6H and 4H polytypes, have no micropipes and a reduced dislocation density [8]. These wafers were proposed to be used as substrates for SiC high-power devices [9]. The main concern regarding these wafers is whether or not the SiC material with filled micropipes can sustain a high electric breakdown field, which is required for high-power device fabrication. Here we describe the first results on silicon carbide homoepitaxial growth on SiC wafers with reduced micropipe density and the characteristics of large area Schottky barriers fabricated on these layers. EXPERIMENTS AND RESULTS Sample Preparation Experiments were done employing TDI's 4H-SiC 35 mm 8-degrees off-axis wafers with reduced micropipe density [7]. These wafers consist of standard commercial 4H-SiC wafers originally having a micropipe density of about 100 per cm 2. The concentration of Nd-Na in the 131 Mat. Res. Soc. Symp. Proc. Vol. 512
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