Microscopic nature of crystal phase quantum dots in ultrathin GaAs nanowires by nanoscale luminescence characterization. (9th June 2016)

• Record Type: Journal Article
• Authors: Loitsch, Bernhard; Müller, Marcus; Winnerl, Julia; Veit, Peter; Rudolph, Daniel; Abstreiter, Gerhard; Finley, Jonathan J; Bertram, Frank; Christen, Jürgen; Koblmüller, Gregor
• Is Part Of: New journal of physics. Volume 18:Number 6(2016:Jun.)
• Publication Date: 2016-06-09
• Subjects: GaAs -- nanowires -- crystal phase polytypism -- cathodoluminescence -- photoluminescence -- quantum dots; Physics -- Periodicals; Physics; Periodicals; 530.05
• DOI: 10.1088/1367-2630/18/6/063009
• Languages: English
• ISSNs: 1367-2630

Abstract

Abstract: Crystal phase quantum dots (CPQD) embedded in a nanowire (NW) geometry have recently emerged as efficient single photon emitters. In typical III–V semiconductor NWs such CPQDs are linked to the well-known zincblende (ZB)/wurtzite (WZ) polytypism that occurs mostly randomly along the NW axis, making it difficult to assess the exact position and microscopic nature of a particular emitter. Here, we employ highly spatially-resolved cathodoluminescence (CL) spectroscopy directly in a scanning transmission electron microscope to unambiguously identify type, microscopic nature, position and luminescence characteristics of single polytype defects in ultrathin GaAs–AlGaAs core–shell NWs with nanometer-scale resolution. Importantly, we find that individual twin defects (1 ML-inclusion of WZ in a ZB crystal) are the predominant source for QD emission, where the spectral position depends sensitively on the strength of radial confinement by the ultrathin GaAs NW core. By analyzing the temperature-dependent luminescence properties of a ∼1 ML thick/7 nm wide twin-defect CPQD, we determine a thermal activation energy of ∼7.4 meV for the confined excitons, as well as an evolution in linewidth that reflects phonon-mediated broadening processes, corroborating the QD-like behavior. Our findings also reveal the presence of effective carrier diffusion in-between isolated CPQDs.