Exciton recombination at crystal-phase quantum rings in GaAs/InxGa1−xAs core/multishell nanowires

Abstract

We study the optical properties of coaxial GaAs/InxGa1−xAs core/multishell nanowires with x between 0.2 and 0.4 at 10 K. The evolution of the photoluminescence energy of the InxGa1−xAs quantum well shell with x and shell thickness agrees with the result of 8-band k·p calculations, demonstrating that the shell growth is pseudomorphic. At low excitation power, the photoluminescence from the shell is dominated by the recombination of exciton states deeply localized within the shell. We show that these states are associated with crystal-phase quantum rings that form at polytype segments of the InxGa1−xAs quantum well shell.

Impact of Outer Shell Structure and Localization Effects on Charge Carrier Dynamics in GaAs/(In,Ga)As Nanowire Core–Shell Quantum Wells

“…Here, we expect that the presence of the AlAs shell next to the shell QW decreases its capture efficiency . Both samples show an additional shoulder at low energies, potentially indicating segments with strong alloy inhomogeneities or crystal phase quantum rings …”

“…For the highest excitation density, a single peak with a full width at half maximum (FWHM) of 50 meV centered at 1.39 eV with a shoulder at 1.44 eV is observed. No luminescence signal from GaAs is detected, not even at high excitation densities, indicating an efficient transfer of charge carriers from the GaAs core to the (In,Ga)As shell QW as observed previously . The high background level at low energies is partly due to the correction of the system response and a finite PL signal at low energies for highest excitation powers.…”

“…The high background level at low energies is partly due to the correction of the system response and a finite PL signal at low energies for highest excitation powers. Possibly from inefficient emission centers at low energy, such as crystal‐phase quantum rings, as evidenced in similar samples from our lab …”

“…Even for the growth of planar (In,Ga)As QWs by MBE, it was shown that roughness and composition inhomogeneities are stronger for growth on the (110) plane compared to the more common (001) plane . Another potential origin of exciton localization in these structures are crystal‐phase quantum rings (CPQRs) which form at the intersection of the QW and zincblende/wurtzite (ZB/WZ) interfaces stemming from a polytypic NW core . Consequently, we attribute the broad luminescence peaks to the inhomogeneity of the material.…”

Correlated Nanoscale Analysis of the Emission from Wurtzite versus Zincblende (In,Ga)As/GaAs Nanowire Core–Shell Quantum Wells

“…Figure 1(c) schematically illustrates the structure, where the QW shell (yellow) and capping layer are known to adopt the crystal structure of the NW core. [32][33][34] The ZB to WZ transition occurs due to a change in growth conditions. The ZB polytype is grown with a relatively low V/III flux ratio.…”