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

“硅化物助熔剂”法合成大β-SiC单晶

基本信息

批准号：
09555211
负责人：
INUI Haruyuki
金额：
$ 7.23万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

项目摘要

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

碳化硅（SiC）作为一种可用于高温高频功率器件的宽带隙半导体，近年来引起了人们的极大兴趣。因为SiC在2400℃左右升华。在环境气氛中，它通常是通过升华法或CVD法生产的。在本研究中，我们旨在开发一种利用过渡金属自杀性熔体作为助熔剂合成β - sic单晶的新方法。这源于我们最近的发现，β - sic晶体是由过渡金属硅化物（如MoSi_2， CrSi_2和CoSi_2）在过共晶成分下形成的初级相。这表明，如果在种子晶附近的熔体中有适当的热梯度，SiC可能会从助熔剂（熔体）中连续析出。通过对WSi_2、TaSi_2、NbSi_2和VSi_2等7种不同过渡金属二硅化剂的熔体长期（至少10小时）稳定性的研究，我们选择了MoSi_2、CrSi_2和CoSi_2作为助熔剂。由于熔体的温度足够高，熔体和坩埚之间可以发生反应，我们选择碳化硅压块作为坩埚。采用艾奇逊法制备的α (6H)-SiC单晶作为种子晶体。当熔体的长期稳定性不够高时，在晶种附近会析出许多mm大小的SiC晶，无法实现单晶生长。电子衍射证实，无论使用何种助熔剂，大多数形成的碳化硅晶体都是β (3C)型。这些碳化硅晶体的纯度似乎非常高，因为通过EDS（能量色散光谱）和CBED（会聚束电子衍射）没有检测到微量杂质（来自相应熔体熔剂的过渡金属原子）。在三种过渡金属二硅化物中，CoSi_2被认为是最有前途的。以CoSi_2为助熔剂可重复生长10小时以上。用CoSi_2制备的最大的SiC单晶在6H SiC晶种C面为mm，在平行于晶种C轴方向为50 mm。在较大的助熔剂量和增大的热梯度下，可以生长出具有较大尺寸的SiC单晶。少