Seo Yong Gon, Shin Sun Hye, Kim Doo Soo, Yoon Hyung-Do, Hwang Sung-Min, Baik Kwang Hyeon
J Nanosci Nanotechnol. 2015 Oct;15(10):7787-90. doi: 10.1166/jnn.2015.11188.
In-plane structural anisotropy is characteristic of nonpolar (1120) a-plane GaN (a-GaN) films grown on r-plane sapphire substrates. The anisotropic peak broadenings of X-ray rocking curves (XRCs) are clearly observed with M- or W-shaped dependence on the azimuth angles. We investigated the optical properties of both M- and W-shaped a-GaN samples with room and low-temperature photoluminescence (PL) measurements. The W-shaped a-GaN film showed higher PL intensity and more compressive strain compared to the M-shaped a-GaN film, whereas the XRC peak widths of the M-shaped a-GaN film on the azimuth angles are lower than those of W-shaped specimens, indicating that better crystalline quality was obtained. We speculate that the PL intensity and strain state of a-GaN layers may be more influenced by the crystallinity of a specific crystal orientation or direction, especially along the m-axis as opposed to the c-axis. This occurrence is most likely due to anisotropic defect distributions, resulting from differences in dangling bond densities of (0001) and {1-100} facets.
面内结构各向异性是生长在r面蓝宝石衬底上的非极性（1120）a面GaN（a-GaN）薄膜的特征。X射线摇摆曲线（XRC）的各向异性峰展宽在方位角上呈现出明显的M形或W形依赖关系，清晰可见。我们通过室温及低温光致发光（PL）测量研究了M形和W形a-GaN样品的光学性质。与M形a-GaN薄膜相比，W形a-GaN薄膜表现出更高的PL强度和更大的压应变，而M形a-GaN薄膜在方位角上的XRC峰宽低于W形样品，这表明M形样品具有更好的晶体质量。我们推测，a-GaN层的PL强度和应变状态可能受特定晶体取向或方向（特别是沿m轴而非c轴）的结晶度影响更大。这种现象很可能是由于（0001）面和{1-100}面悬空键密度的差异导致的各向异性缺陷分布所致。
