Synthesis of large beta-SiC single crystals by 'silicide-flux'method

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Silicon carbide (SiC) has attracted considerable interest in recent years as a wide band-gap semiconductor that can be used in high-temperature high-frequency power device applications. Since SiC sublimes at about 2400。C in ambient atmosphere, it is usually produced either by sublimation methods or by CVD methods. In the present study, we have aimed at developing a new method for synthesis of beta-SiC single crystals utilizing melts of transition-metal suicides as a flux. This stems from our recent finding that beta-SiC crystallites are formed as a primary phase from melts of transition-metal silicides (such as MoSi_2, CrSi_2 and CoSi_2) at hyper-eutectic compositions. This results suggests that if we have an appropriate thermal gradient in the melts near a seed crystal, SiC may precipitate from the flux (melt) continuously on the seed crystal. We have chosen MoSi_2, CrSi_2 and CoSi_2 as a flux from investigations of the long-term (at least, for 10 hours) stability of a melt for seven … More different transition-metal disilicides including WSi_2, TaSi_2, NbSi_2 and VSi_2. Since the temperature of melts is high enough for the reaction between a melt and crucible to occur, we have chosen SiC compacts as a crucible. alpha(6H)-SiC single crystals produced by the Acheson method are used as a seed crystal. When the long-term stability of melts is not high enough, many SiC crystallites of mm-sizes precipitated near the seed crystal and single-crystal growth can not be achieved. Electron diffraction has confirmed that most SiC crystallites formed are of the beta(3C)-type, regardless of fluxes used. The purity of these SiC crystallites seems to be very high since no trace of impurities (transition-metal atoms from the corresponding melt flux) is detected by EDS (energydispersive spectroscopy) and CBED (convergent-beam electron diffraction). Of the three transitionmetal disilicides, CoSi_2 is found to be the most promising. Crystal growth for more than ten hours can be reproducibly made with CoSi_2 as a flux. The largest SiC single crystal produced with CoSi_2 is mm-size in the C plane of the 6H SiC seed crystal and 50 mum in the direction parallel to the C-axis of the seed crystal. Growth of SiC single crystals with larger dimensions may be possible with a larger amount of fluxes and an increased thermal gradient. Less