Reconstruction and Epitaxial Adlayers on SiC Surfaces: Structural Significance for Technological Applications
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Reconstruction and Epitaxial Adlayers on SiC Surfaces: Structural Significance for Technological Applications U. Starke Max-Planck-Institut f¨ ur Festk¨orperforschung, Stuttgart, Germany. ABSTRACT Structure and composition are reviewed for different surface phases of SiC(0001) and SiC(000¯1). The chemistry of well ordered phases spans from Si rich to graphitic composition with the excess elements arranged in adlayers and/or large scale reconstruction patterns. On SiC(0001) the Si rich (3×3) surface allows for step flow growth of monocrystalline homoepitaxial layers due to an extremely efficient dangling bond saturation. Si rich preparation or oxidative are used for a controlled evolution of different stacking √ √treatment ◦ sequences on the ( 3× 3)R30 adatom phase on SiC(0001) and could be utilized for the development of polytype heterostructures. On SiC(000¯1) a (2×2) phase shows three-fold coordinated adatoms with a different surface stacking reflecting the different growth behaviour of this surface. An epitaxially well matching silicon oxide monolayer can be prepared on both surface orientations by using a hydrogen etching or plasma treatment promising to facilitate low defect oxide films for MOS devices.
INTRODUCTION High power, high frequency and high temperature device applications have made silicon carbide an interesting wide-band gap semiconductor. The quality of SiC material available for the device production process is in particular important for an industrial application. A severe problem arises in the case of SiC owing to the equal stability of different crystal structures (polytypes) [1]. So, for a sufficient crystallinity the development of growth methods suitable to obtain homo-polytype, well ordered crystalline films on top of bulk grown substrate wafers is required. An important technological issue is the quality of oxide layers grown on SiC for MOSFET devices and for passivation layers of low defect density. The interface state density which is one of the most relevant factors for the performance of a device is strongly influenced by structural defects such as unsaturated dangling bonds. Even though the SiC and SiO2 lattice parameters match within about 5% potentially allowing for an epitaxial SiC/SiO2 interface – in contrast to Si with a 25% misfit – the electronic quality of the substrate-oxide interface is much worse for SiC [2, 3] than for Si. So, obviously a better control of the oxidation or oxide deposition process is necessary in order to utilize the full potential of SiC for electronic devices. Last but not least, with the different band gaps of different polytypes [4] and their lattice parameters parallel to the hexagonal bilayers being practically equal, the development of strain free heterostructures composed from different polytypes appears feasible. For this kind of application one needs to switch between different polytypes during growth and obtain sharp, well defined polytype interfaces, which of course requires flat surfaces during growth. These examples demonstrate that
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