Shenyang National Laboratory for Materials Science (SYNL), Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS), No. 72, Wenhua Road, Shenhe District, Shenyang 110016, China.
Nanoscale. 2017 Apr 20;9(16):5212-5221. doi: 10.1039/c7nr00032d.
Well-aligned GaN nanowires are promising candidates for building high-performance optoelectronic nanodevices. In this work, we demonstrate the epitaxial growth of well-aligned GaN nanowires on a [0001]-oriented sapphire substrate in a simple catalyst-assisted chemical vapor deposition process and their alignment control. It is found that the ammonia flux plays a key role in dominating the initial nucleation of GaN nanocrystals and their orientation. Typically, significant improvement of the GaN nanowire alignment can be realized at a low NH flow rate. X-ray diffraction and cross-sectional scanning electron microscopy studies further verified the preferential orientation of GaN nanowires along the [0001] direction. The growth mechanism of GaN nanowire arrays is also well studied based on cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization and it is observed that GaN nanowires have good epitaxial growth on the sapphire substrate following the crystallographic relationship between (0001)∥(0001) and (101[combining macron]0)∥(112[combining macron]0). Most importantly, periodic misfit dislocations are also experimentally observed in the interface region due to the large lattice mismatch between the GaN nanowire and the sapphire substrate, and the formation of such dislocations will favor the release of structural strain in GaN nanowires. HRTEM analysis also finds the existence of "type I" stacking faults and voids inside the GaN nanowires. Optical investigation suggests that the GaN nanowire arrays have strong emission in the UV range, suggesting their crystalline nature and chemical purity. The achievement of aligned GaN nanowires will further promote the wide applications of GaN nanostructures toward diverse high-performance optoelectronic nanodevices including nano-LEDs, photovoltaic cells, photodetectors etc.
取向良好的 GaN 纳米线是构建高性能光电纳米器件的有前途的候选材料。在这项工作中，我们在简单的催化剂辅助化学气相沉积工艺中展示了在[0001]取向的蓝宝石衬底上外延生长取向良好的 GaN 纳米线及其对准控制。研究发现，氨气流在控制 GaN 纳米晶的初始成核及其取向方面起着关键作用。通常，在低 NH 流速下可以实现 GaN 纳米线对准度的显著提高。X 射线衍射和横截面扫描电子显微镜研究进一步证实了 GaN 纳米线沿[0001]方向的择优取向。还通过横截面高分辨率透射电子显微镜（HRTEM）表征对 GaN 纳米线阵列的生长机制进行了深入研究，观察到 GaN 纳米线在蓝宝石衬底上具有良好的外延生长，遵循（0001）∥（0001）和（101[combining macron]0）∥（112[combining macron]0）之间的晶体关系。最重要的是，由于 GaN 纳米线与蓝宝石衬底之间的晶格失配较大，在界面区域还实验观察到周期性失配位错，这种位错的形成有利于 GaN 纳米线中结构应变的释放。HRTEM 分析还发现 GaN 纳米线内部存在“Ⅰ型”堆垛层错和空洞。光学研究表明，GaN 纳米线阵列在 UV 范围内具有强烈的发射，表明其结晶性质和化学纯度。取向 GaN 纳米线的实现将进一步推动 GaN 纳米结构在各种高性能光电纳米器件中的广泛应用，包括纳米 LED、光伏电池、光电探测器等。
