Multi-quantum-well polaritons in semiconductor nanocolumns

本计画的目的是观察GaN及InGaN/GaN奈米柱中的多量子井极化激元耦合。然而，我们没有观察到极化激元耦合，因为纳米柱中的量子威尔斯具有不同的共振能量。我们已经观察到奇特的光学性质，由于纳米柱形态。我们研究了GaN纳米柱的特殊光学性质，着重研究了柱的形状对GaN纳米柱的光学性质的影响，在大直径（~ 100 nm）的GaN纳米柱的光致发光（PL）谱中，出现了两个分别属于自由A激子（A）和束缚激子（I）的峰。随着直径减小，出现能量位置对应于B-激子（B）和C-激子（C）的较高能量峰。为了阐明这一点的起源，我们计算了考虑激子的极化激元效应的GaN纳米柱的PL光谱;即，考虑从纳米柱的顶表面和侧表面的传播和辐射。结果表明，随着直径的减小，B和C激子的发光峰变得明显，这是因为侧面的光致发光变得很重要;我们还观察到大直径GaN纳米柱中的双激子发光，发现双激子结合能比体样品中的高。虽然结合能增加的机制目前还不清楚，我们认为它是由于纳米柱形态的空间限制效应。

The purpose of this project was to observe multi-quantum-well polariton coupling in GaN and InGaN/GaN nanocolumns. However we have not observed the polariton coupling, because quantum wells in the nanocolumns have different resonance energies. We have observed peculiar optical properties due to the nanocolumn morphology. We have studied specific optical properties of the GaN nanocolumn, focusing on the influence of the columnar shape.In photoluminescence (PL) spectrum of GaN nanocolumns with large diameters (〜100nm) there are two peaks attributed to free A-excitons (A) and bound excitons (I). With decreasing the diameter, higher-energy peaks whose energy positions correspond to B-excitons (B) and C-excitons (C) appear. In order to elucidate the origin of this, we calculated PL spectra of GaN nanocolumns considering the polaritonic effect of the excitons; i.e. considering propagation and radiation from both the top and the side surfaces of the nanocolumns. The results show that the peaks of B and C excitons become remarkable with decreasing the diameter because PL from the side surface becomes important.We also observed biexciton emissions in GaN nanocolumns with large diameters, and found that the biexciton binding energies are higher than that in bulk samples. Although the mechanism for the increase in the binding energy is not clear at the present, we suppose that it arises from spatial confinement effect due to the nanocolumn morphology.