Physics Department, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece.
Nanotechnology. 2013 Nov 1;24(43):435702. doi: 10.1088/0957-4484/24/43/435702. Epub 2013 Sep 27.
The structural properties and the strain state of InGaN/GaN superlattices embedded in GaN nanowires were analyzed as a function of superlattice growth temperature, using complementary transmission electron microscopy techniques supplemented by optical analysis using photoluminescence and spatially resolved microphotoluminescence spectroscopy. A truncated pyramidal shape was observed for the 4 nm thick InGaN inclusions, where their (0001¯) central facet was delimited by six-fold {101¯l} facets towards the m-plane sidewalls of the nanowires. The defect content of the nanowires comprised multiple basal stacking faults localized at the GaN base/superlattice interface, causing the formation of zinc-blende cubic regions, and often single stacking faults at the GaN/InGaN bilayer interfaces. No misfit dislocations or cracks were detected in the heterostructure, implying a fully strained configuration. Geometrical phase analysis showed a rather uniform radial distribution of elastic strain in the (0001¯) facet of the InGaN inclusions. Depending on the superlattice growth temperature, the elastic strain energy is partitioned among the successive InGaN/GaN layers in the case of low-temperature growth, while at higher superlattice growth temperature the in-plane tensile misfit strain of the GaN barriers is accommodated through restrained diffusion of indium from the preceding InGaN layers. The corresponding In contents of the central facet were estimated at 0.42 and 0.25, respectively. However, in the latter case, successful reproduction of the experimental electron microscopy images by image simulations was only feasible, allowing for a much higher occupancy of indium adatoms at lattice sites of the semipolar facets, compared to the invariable 25% assigned to the polar facet. Thus, a high complexity in indium incorporation and strain allocation between the different crystallographic facets of the InGaN inclusions is anticipated and supported by the results of photoluminescence and spatially resolved microphotoluminescence spectroscopy.
氮化镓纳米线中嵌入的 InGaN/GaN 超晶格的结构特性和应变状态随超晶格生长温度的变化进行了分析，使用互补的透射电子显微镜技术，并辅以光分析，包括光致发光和空间分辨微光致发光光谱学。对于 4nm 厚的 InGaN 夹杂，观察到了截断的金字塔形状，其（0001¯）中心面由六个六重 {101¯l} 面朝向纳米线的 m 面侧壁限定。纳米线的缺陷含量包括局部化在 GaN 基底/超晶格界面处的多个基底堆垛层错，导致形成闪锌矿立方区域，并且经常在 GaN/InGaN 双层界面处存在单个堆垛层错。在异质结构中未检测到失配位错或裂纹，这意味着完全处于应变状态。几何相位分析表明，InGaN 夹杂的（0001¯）面具有相当均匀的径向弹性应变分布。根据超晶格生长温度的不同，在低温生长的情况下，弹性应变能在连续的 InGaN/GaN 层之间分配，而在较高的超晶格生长温度下，GaN 势垒的面内拉伸失配应变通过抑制铟从先前的 InGaN 层中扩散来得到缓解。中心面的相应 In 含量分别估计为 0.42 和 0.25。然而，在后一种情况下，通过图像模拟成功再现了实验电子显微镜图像，这使得半极性面的晶格位置上的铟占据原子的占有率大大提高，与分配给极性面的不变的 25%相比。因此，预计 InGaN 夹杂的不同结晶面之间的 In 掺入和应变分配具有很高的复杂性，这得到了光致发光和空间分辨微光致发光光谱学的结果的支持。
