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

降低III族氮化物薄膜中的缺陷密度（特别是穿透位错）对于获得高性能的光学和电学器件具有重要意义。由于缺乏块状GaN衬底，因此不得不使用异质材料作为衬底，例如蓝宝石和SiC，因此III族氮化物的生长通过异质外延来完成。在许多潜在的问题，以解决减少偏转密度在III族氮化物薄膜生长衬底表面结构和形貌在原子尺度上是本质上重要的课题。我们特别注意到SiC表面，其通常在原样条件下显示出相当粗糙的形态。我们最初发现，这种表面特征仅在6 H-SiC（0001）上通过高温（约1400℃）氢气（约14%HCl）蚀刻得到改善，从而得到原子级光滑的表面。实际上，该过程影响AlN和GaN异质薄膜中结构偏转的引入。还蚀刻邻近衬底，4度偏离6 H-SiC（0001）和8度偏离4 H-SiC（0001），以观察是否观察到类似的平滑化效果。两个相邻的SiC表面表示规则间隔的步骤/梯田结构在纳米尺度。研究了这种有序结构的起源，发现表面由纳米晶面组成;（0001）和（11-2n），这是由于表面相分离使表面自由能最小化。这种nanofacet对的顺序被认为是与量子阶聚束和小面-小面相互作用。重要的是，前者在很大程度上归因于与常规立方半导体（Si和GaAs）相比的上级周期性，这是由于SiC的多型性质。我们研究了GaN的成核和生长在相邻的SiC表面与周期性的nanofacets和显示各向异性的结构特性，从而减少缺陷密度的含义。

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.