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

碳化硅作为一种可应用于高温高频功率器件的宽禁带半导体材料，近年来引起了人们的极大兴趣。因为碳化硅在2400左右升华。在大气中，它通常通过升华或CVD方法产生。在本研究中，我们致力于开发一种利用过渡金属自杀剂熔体作为助熔剂来合成β-碳化硅单晶的新方法。这是因为我们最近发现，过渡金属硅化物(如MoSi2、CrSi2和CoSi2)的熔体在过共晶成分下作为初生相形成了β-碳化硅微晶。这一结果表明，如果在种子晶体附近的熔体中有适当的温度梯度，则可能会从种子晶体上的熔剂(熔体)中连续析出碳化硅。通过对熔体在7…下的长期(至少10小时)稳定性的研究，我们选择了MoSi2，CrSi2和CoSi2作为熔剂更多的过渡金属二硅化物，包括WSi_2，TaSi_2，NbSi_2和VSi_2。由于熔体的温度足够高，熔体与坩埚之间发生反应，我们选择了碳化硅压坯作为坩埚。用艾奇逊法生长的α(6H)-碳化硅单晶作为晶种。当熔体的长期稳定性不够高时，在晶种附近析出许多毫米级的碳化硅微晶，不能实现单晶生长。电子衍射证实，无论使用何种助熔剂，所形成的大多数碳化硅微晶都是β(3C)型的。这些碳化硅微晶的纯度似乎很高，因为EDS(能谱)和CBED(会聚束电子衍射)没有检测到任何杂质(来自相应熔剂的过渡金属原子)。在三种过渡金属二硅化物中，CoSi_2是最有前途的。用CoSi2作助熔剂，可重复生长十几个小时以上的晶体。用CoSi2生长出的最大单晶尺寸在6H碳化硅晶种的C面上为毫米，在平行于晶种晶体C轴的方向上为50微米。更多的助熔剂和更高的温度梯度可以生长出尺寸更大的碳化硅单晶。较少

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