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0911-B14-03

Alternative Magnesium Calcium Oxide Gate Dielectric for Silicon Carbide MOS Application D. O. Stodilka1, A. P. Gerger1, M. Hlad1, P. Kumar1, B. P. Gila1, R. Singh1,2, C. R. Abernathy1, S. J. Pearton1, and F. Ren3 1 Dept. of Materials Science and Engineering, University of Florida, Gainesville, FL, 32611 2 Sinmat Inc., Gainesville, FL, 32641 3 Dept. of Chemical Engineering, University of Florida, Gainesville, FL, 32611

ABSTRACT Films of MgO and MgCaO ternaries were grown at low temperature as dielectrics on 6HSiC by gas-source MBE. MgO grown at 300 and 400°C revealed crystallites textured toward the (111) orientation on SiC (0001). A solid-solution Mg.75Ca.25O ternary was grown having a minimal lattice mismatch and low root mean square (RMS) roughness of 0.5 nm. SiC pretreatments in UV-ozone reduced carbon contaminants on the surface of SiC, but resulted in the increase of fixed oxide charge in the oxide/SiC interface. Electrical breakdown fields >3.5 MV cm-1 and low density of interface states on the order of 1011 cm-2eV-1 were achieved for a Mg.75Ca.25O ternary grown at 300°C. These oxides are presented for the first time as low temperature alternatives to SiO2 gate dielectrics for SiC MOS applications. INTRODUCTION The diversity of applications for SiC-based devices is widespread due to the physical nature of the SiC semiconductor such as its wide bandgap, high thermal conductivity, and high breakdown field strength. Fabrication of these devices is made possible by processes conventionally used for Si-based devices, such as the thermal oxidation of SiC to form SiO2. However, several studies have reported electrical instabilities at the SiO2/SiC surface due to the low dielectric constant of SiO2 and its charged ion diffusion at elevated temperatures [1]. Problems associated with thermally grown oxides may be alleviated by the use of high κ dielectric films such as Al2O3 [2] or HfO2 [3]. In this work, two other possibilities, MgO and a solid solution MgxCa1-xO ternary, are demonstrated as alternative dielectrics to SiO2 due to favorable properties such as high dielectric constant, wide bandgap, and notable lattice compatibility with SiC. MgO is a rock salt crystal that has been explored an intermediate buffer layer for growth of ferroelectrics [4,5], and as a potential gate dielectric for Si [5] or GaAs [6]. Growth of MgO on Si and GaAs by MBE has had limited success due to large lattice mismatch. SiC has a smaller lattice constant than GaAs and is thus a much closer match to MgO. CaO, also rock salt, has a substantially larger lattice spacing than MgO [7]. In principle, a ternary oxide consisting of MgO and CaO could be alloyed to match SiC resulting in a substantial reduction in film and interface defects. Another favorable properties of this system are the wide bandgaps of MgO (8 eV) and CaO (7 eV). Thus large band offsets are expected relative to either n- or p-type SiC.

Furthermore, the dielectric constants of both MgO (9.8) and CaO (11.8) are significantly higher than SiO2 (3.9). The drawback o