Luminescence of GaAs nanowires consisting of wurtzite and zincblende segments

TL;DR

This study investigates the luminescence properties of GaAs nanowires with mixed zincblende and wurtzite phases, revealing how their band alignments and segment thickness influence optical emission energies.

Contribution

It provides experimental evidence that GaAs nanowires with mixed phases exhibit type II band alignment, affecting their emission energies based on segment confinement and temperature.

Findings

Wurtzite GaAs band gap is at least 55 meV larger than zincblende.

Optical emission can occur above or below the zincblende band gap.

Carbon acceptors influence spectral profiles at low temperatures.

Abstract

GaAs nanowires (NWs) grown by molecular-beam epitaxy may contain segments of both the zincblende (ZB) and wurtzite (WZ) phases. Depending on the growth conditions, we find that optical emission of such NWs occurs either predominantly above or below the band gap energy of ZB GaAs [E(g,ZB)]. This result is consistent with the assumption that the band gap energy of wurtzite GaAs [E(g,WZ)] is larger than E(g,ZB) and that GaAs NWs with alternating ZB and WZ segments along the wire axis establish a type II band alignment, where electrons captured within the ZB segments recombine with holes of the neighboring WZ segments. Thus, the corresponding transition energy depends on the degree of confinement of the electrons, and transition energies exceeding E(g,ZB) are possible for very thin ZB segments. At low temperatures, the incorporation of carbon acceptors plays a major role in determining the spectral profile as these can effectively bind holes in the ZB segments. From cathodoluminescence measurements of single GaAs NWs performed at room temperature, we deduce a lower bound of 55 meV for the difference E(g,WZ)-E(g,ZB).