Heteroepitaxy in III-nitride semiconductors by means of control of surface structures in atomistic scale.

降低氮化族薄膜的缺陷密度（特别是螺纹位错）对实现高性能光电器件具有重要意义。由于缺乏块状氮化镓衬底，它不得不使用外来材料作为衬底，例如蓝宝石和SiC，因此iii -氮化物的生长是通过异质外延完成的。在降低iii -氮化物薄膜偏转密度的许多潜在问题中，衬底的表面结构和形貌在原子尺度上是必不可少的重要课题。我们特别注意到SiC表面，通常在接收条件下表现出相当粗糙的形貌。我们最初发现，仅6H-SiC（0001）的这种表面特征通过高温（~ 1400℃）氢气（含~ 14% HCl）蚀刻得到改善，导致表面原子光滑。事实上，这一过程影响了AIN和GaN异质薄膜中结构偏转的引入。邻近的衬底，4度的6H-SiC（0001）和8度的4H-SiC(0001)，也被蚀刻，看看是否观察到类似的平滑效果。相邻的两个SiC表面在纳米尺度上显示出规则间隔的台阶/阶地结构。研究了这种有序结构的起源，发现表面由纳米面组成；（0001）和（11-2n），由于表面相分离使表面自由能最小。用量子阶跃聚束和面-面相互作用来考虑这种纳米面对的排序。重要的是，由于SiC的多晶性，前者与传统的立方半导体（Si和GaAs）相比具有优越的周期性。我们研究了氮化镓在具有周期性纳米晶面的相邻SiC表面上的成核和生长，并显示出各向异性的结构特征，从而暗示了缺陷密度的降低。

Reduction of defect density (especially threading dislocations) in group III-nitride thin films is of great importance to achieve high performance optical and electrical devise. Due to the lack of bulk GaN substrate it is obliged to use foreign materials as a substrate, e.g.sapphire and SiC, and thus growth of III-nitrides is done by a heteroepitaxy. Among many potential problems to solve for the reduced deflect density in III-nitride thin film growth substrate surface structures and morphologies in atomistic scale are essentially important topics. We especially noticed SiC surfaces, which normally show rather rough morphology at the as-received condition. We initially found that such surface features on just 6H-SiC(0001) were improved by high temperature (〜1400℃) hydrogen gas (with 〜14% HCl) etching, resulting in atomically smooth surfaces. Indeed, this process affects the introduction of structural deflects in AIN and GaN hetero-thin films. Vicinal substrates, 4-degree-off 6H-SiC(0001) and 8-degree-off 4H-SiC(0001), were also etched to see if similar smoothening effects were observed. Both vicinal SiC surfaces indicated regularly spaced step/terrace structures in nanometer scale. The origins of such ordering structures were investigated and found that the surfaces consist of nanofacets; (0001) and (11-2n), due to surface phase separation in minimizing surface free energies. The ordering of such nanofacet pairs is considered with quantum step bunching and facet-facet interactions. Importantly the former is greatly attributed to superior periodicity compared to conventional cubic semiconductors (Si and GaAs), owing to polytymorpholic nature of SiC. We investigated GaN nucleation and growth on vicinal SiC surfaces with periodic nanofacets and showed anisotropic structural characteristics and thus implication of reduction of the defect density.