对热壁化学气相沉积法(HWCVD)在6H-SiC(0001)面上外延生长的SiCGe薄膜结构进行了机理分析.SiCGe薄膜具有球形岛和三角形层状堆叠岛两种岛状结构,球形岛为金刚石型结构,而三角形层状堆叠岛则为闪锌矿型结构.认为球形岛是Ge富集后,高温析出形成的,而三角岛则是堆垛层错形成四面体的露头.生长温度的变化会引起球形岛和三角岛的相互转变,其原因主要有两方面:一方面,高温时,立方SiC相比SiCGe相更为稳定,随着温度的升高,SiCGe相逐渐向SiC相转变,替位式的Ge原子的数量会有所下降,从而使SiCFe外延层和SiC衬底间的晶格失配度减小,于是薄膜的生长模式由3D岛状变为2D生长,仅仅靠产生三角形堆垛层错释放失配应力;另一方面,生长温度越高,原子能量就越大,达到理想位置的原子比例越高,就会表现出材料本身的结构特征,而面心立方的{111}面上这种结构特征的体现就是三角形堆垛层错的产生.
The growth mechanism of SiCGe films grown on SiC is analyzed by hot wall chemical vapor deposition ( HWCVD) . The SiCGe epilayer has two types of island structures, spherical islands with diamond cubic structure and cascading triangular islands with zinc-blende structure. The spherical island is produced by the precipitation Ge phase at high temperature, while the cascading triangular island is the outcrop of stacking fault tetrahedron. Two reasons for the transition between the spherical and cascading triangular islands are disscussed. At high temperature, SiC phase is more stable than SiCGe phase, hence Ge content is decreased in the SiCGe film, which reduces the mismatch strain between the epilayer and the substrate, thus enhances the 2D growth and makes the spherical island change into the cascading triangular islands. Higher growth temperature makes the atom energy greater, thus more atoms can be in the ideal position, and the material will exhibit structural characteristics, which is the producing of the cascading triangular island.
参考文献
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