Reznik Rodion R, Cirlin George E, Kotlyar Konstantin P, Ilkiv Igor V, Akopian Nika, Leandro Lorenzo, Nikolaev Valentin V, Belonovski Alexey V, Kaliteevski Mikhail A
Alferov University, Khlopina St. 8/3, 194021 St. Petersburg, Russia.
St. Petersburg State University, 13B Universitetskaya Emb, 198504 St. Petersburg, Russia.
Nanomaterials (Basel). 2021 Oct 29;11(11):2894. doi: 10.3390/nano11112894.
Control of directionality of emissions is an important task for the realization of novel nanophotonic devices based on nanowires. Most of the existing approaches providing high directionality of the light emitted from nanowires are based on the utilization of the tapered shape of nanowires, serving as nanoantenna coupling with the light waveguided in nanowire and the directional output beam. Here we report the beaming of the emitted light with wavelength near 800 nm by naturally formed core-shell AlGaAs NW with multiply GaAs quantum dots (QDs) diameter 30 nm and height 10 nm, while the diameter of NW 130 nm, what does not support efficient emission into waveguided modes, including the mode HE. Experimental measurements show that intensity of emission for directions in the vicinity of the axis of NW is about two orders of magnitude higher than for perpendicular directions. The developed theoretical approach allowed us to calculate the probability of spontaneous emission for various directions and into waveguided modes and showed that highly directional radiation can be provided by the intrinsic emission properties of cylindrical NW. Our results suggest that for the small diameter of NW, directional emissions are associated with an TM leaky mode (when electric field oriented in axial direction) and therefore manifests in an existence of axial electric dipole transitions in quantum dots.
控制发射的方向性是实现基于纳米线的新型纳米光子器件的一项重要任务。现有的大多数实现纳米线发射光高方向性的方法都是基于利用纳米线的锥形形状，其作为纳米天线与在纳米线中波导的光以及定向输出光束耦合。在此，我们报道了由自然形成的具有多个直径为30 nm、高度为10 nm的GaAs量子点（QD）的核壳AlGaAs纳米线对波长接近800 nm的发射光进行定向发射，而纳米线的直径为130 nm，这并不支持高效发射到包括HE模式在内的波导模式中。实验测量表明，在纳米线轴附近方向的发射强度比垂直方向的发射强度高约两个数量级。所开发的理论方法使我们能够计算不同方向以及进入波导模式的自发发射概率，并表明圆柱形纳米线的固有发射特性可以提供高方向性辐射。我们的结果表明，对于小直径的纳米线，定向发射与TM泄漏模式相关（当电场沿轴向取向时），因此表现为量子点中存在轴向电偶极跃迁。
