Determination of the optimal shell thickness for self-catalysed GaAs/AlGaAs core-shell nanowires

TL;DR

This study investigates how the thickness of AlGaAs shells affects carrier dynamics in self-catalyzed GaAs/AlGaAs nanowires, revealing an optimal shell thickness for enhanced luminescence and minimal defects.

Contribution

It provides experimental insights into the optimal shell thickness for GaAs/AlGaAs nanowires to maximize luminescence efficiency and minimize defects, considering surface effects and structural quality.

Findings

7 nm shell reduces surface recombination effectively

Shell thickness over 50 nm causes defect formation

Carrier diffusion length varies non-monotonically with shell thickness

Abstract

We present a set of experimental results identifying various effects that govern the carrier dynamics of self-catalyzed GaAs/AlGaAs core-shell nanowires (NWs) grown by molecular beam epitaxy i.e. surface recombination velocity, surface charge traps, and structural defects. Time-resolved photoluminescence of NW ensemble and spatially-resolved cathodoluminescence of single NWs reveal that emission intensity, decay time and carrier diffusion length of the GaAs NW cores strongly depend on AlGaAs shell thickness but in a non-monotonic fashion. Although 7 nm-AlGaAs shell can efficiently suppress the surface recombination velocity of the GaAs NW cores, the effect of the band bending caused by the surface charges remains dominant if the shell thickness is less than 50 nm; that is, the carrier diffusion length is smaller in the NWs with a thinner shell caused by a stronger carrier scattering at the core/shell interface. If the AlGaAs shell thickness is larger than 50 nm, the luminescence efficiency of the GaAs NW cores starts to be deteriorated, ascribed to the defect formation inside the AlGaAs shell evidenced by transmission electron microscopy.