There is common agreement that dimensional downscaling of III-nitride light-emitting diodes leads to spectral blue shifts due to strain relaxation of the quantum wells (QWs). Near-field photoluminescence (nf-PL) mapping of micropillars with InGaN/GaN QWs of different indium compositions using scanning near-field optical spectroscopy reveals that the nf-PL spectrum blue-shifts at the edge of a micropillar with respect to the center for QWs with a high indium composition, whereas a relative red shift is observed for QWs with a low indium composition. This observation suggests that the strain relaxation mechanism in micropillars is dependent on the indium composition, evident from changes in lattice parameters determined from calibrated diffraction patterns obtained by transmission electron microscopy. As indicated by molecular dynamics simulations, the strain of a micropillar is influenced by competing strain relaxation mechanisms between the lattice mismatch strain from the QWs, and residual strain from other layers and their interactions with the edge of the micropillar. First-principle calculations of GaN/InGaN/GaN heterostructures confirmed the effect of strain relaxation on the potential profiles, and, thus, on the spectral shifts from the micropillars. The findings of this work provide insight into strain-induced band profile engineering in optoelectronic devices built on lattice-mismatched systems.

中文翻译：

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解释InGaN / GaN微柱中的相对光谱红移

人们普遍同意，由于量子阱（QW）的应变弛豫，III型氮化物发光二极管的尺寸缩小会导致光谱蓝移。使用扫描近场光学光谱法对具有不同铟组成的InGaN / GaN QW的微柱进行近场光致发光（nf-PL）映射，结果显示，nf-PL光谱在微柱边缘相对于中心的蓝移铟成分较高的量子阱，相对而言对于铟含量低的QW，观察到红移。该观察结果表明，微柱中的应变松弛机制取决于铟的组成，这从通过透射电子显微镜获得的校准衍射图确定的晶格参数变化中可以明显看出。如分子动力学模拟所示，微柱的应变受QW的晶格失配应变与其他层的残余应变及其与微柱边缘的相互作用之间竞争性的应变松弛机制的影响。GaN / InGaN / GaN异质结构的第一性原理计算证实了应变松弛对电势分布的影响，因此也对来自微柱的光谱偏移产生了影响。