Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
Walter Schottky Institut, Physik Department, and Center of Nanotechnology and Nanomaterials, Technische Universität München , 85748 Garching, Germany.
ACS Nano. 2015 Aug 25;9(8):8335-43. doi: 10.1021/acsnano.5b04070. Epub 2015 Aug 4.
GaAs-AlxGa1-xAs (AlGaAs) core-shell nanowires show great promise for nanoscale electronic and optoelectronic devices, but the application of these nonplanar heterostructures in devices requires improved understanding and control of nanoscale alloy composition and interfaces. Multiple researchers have observed sharp emission lines of unknown origin below the AlGaAs band edge in photoluminescence (PL) spectra of core-shell nanowires; point defects, alloy composition fluctuations, and self-assembled quantum dots have been put forward as candidate structures. Here we employ laser-assisted atom probe tomography to reveal structural and compositional features that give rise to the sharp PL emission spectra. Nanoscale ellipsoidal Ga-enriched clusters resulting from random composition fluctuations are identified in the AlGaAs shell, and their compositions, size distributions, and interface characteristics are analyzed. Simulations of exciton transition energies in ellipsoidal quantum dots are used to relate the Ga nanocluster distribution with the distribution of sharp PL emission lines. We conclude that the Ga rich clusters can act as discrete emitters provided that the major diameter is ≥4 nm. Smaller clusters are under-represented in the PL spectrum, and spectral lines of larger clusters are broadened, due to quantum tunneling between clusters.
砷化镓-铝镓砷（AlGaAs）核壳纳米线在纳米尺度电子和光电子器件方面具有巨大的应用前景，但这些非平面异质结构在器件中的应用需要对纳米尺度合金成分和界面有更好的理解和控制。多位研究人员在核壳纳米线的光致发光（PL）光谱中观察到了在 AlGaAs 带边以下的未知来源的尖锐发射线；点缺陷、合金成分波动和自组装量子点已被提出作为候选结构。在这里，我们采用激光辅助原子探针层析技术来揭示导致尖锐 PL 发射光谱的结构和组成特征。在 AlGaAs 壳中识别出了由随机成分波动产生的纳米尺度的椭球形富 Ga 团簇，并对其成分、尺寸分布和界面特性进行了分析。通过模拟在椭球量子点中的激子跃迁能量，将 Ga 纳米团簇的分布与尖锐的 PL 发射线的分布联系起来。我们的结论是，只要主要直径≥4nm，富 Ga 团簇就可以作为离散的发射器。由于团簇之间的量子隧穿，较小的团簇在 PL 光谱中代表性不足，较大团簇的谱线变宽。
