Bismuth surfactant-enhanced III-As epitaxy on GaAs(111)A

TL;DR

This study demonstrates that bismuth surfactants improve the surface quality of GaAs(111)A epitaxy and induce a transition in InAs growth mode, enabling the development of high-symmetry quantum dots for quantum photonics.

Contribution

The paper introduces the use of bismuth as a surfactant in III-As MBE on GaAs(111)A, showing it reduces surface defects and promotes 3D nanostructure formation, a novel approach for quantum dot fabrication.

Findings

Bi reduces surface roughness to 0.13 nm RMS.

Bi increases adatom diffusion on GaAs(111)A.

Bi induces a morphological transition in InAs growth.

Abstract

Quantum dot (QD) growth on high ($c_{3v}$) symmetry GaAs{111} surfaces holds promise for efficient entangled photon sources. Unfortunately, homoepitaxy on GaAs{111} surfaces suffers from surface roughness/defects and InAs deposition does not natively support Stranski-Krastanov (SK) QD growth. Surfactants have been identified as effective tools to alter the epitaxial growth process of III-V materials, however, their use remains unexplored on GaAs{111}. Here, we investigate Bi as a surfactant in III-As molecular beam epitaxy (MBE) on GaAs(111)A substrates, demonstrating that Bi can eliminate surface defects/hillocks in GaAs and (Al,Ga)As layers, yielding atomically-smooth hillock-free surfaces with RMS roughness values as low as 0.13 nm. Increasing Bi fluxes are found to result in smoother surfaces and Bi is observed to increase adatom diffusion. The Bi surfactant is also shown to trigger a morphological transition in InAs/GaAs(111)A films, directing the 2D InAs layer to rearrange into 3D nanostructures, which are promising candidates for high-symmetry quantum dots. The desorption activation energy ($U_{Des}$) of Bi on GaAs(111)A was measured by reflection high energy electron diffraction (RHEED), yielding $U_{Des}$ = 1.7 $\pm$ 0.4 eV. These results illustrate the potential of Bi surfactants on GaAs(111)A and will help pave the way for GaAs(111)A as a platform for technological applications including quantum photonics.