Uniaxial stress flips the natural quantization axis of a quantum dot for integrated quantum photonics

Xueyong Yuan,Rinaldo Trotta,Fritz Weyhausen-Brinkmann,Oliver G Schmidt,Gabriel Bester,Yongheng Huo,Armando Rastelli,Johannes Edlinger,Giovanni Piredda,Javier Martín-Sánchez,Christian Schimpf,Huiying Huang,Vlastimil Křápek

doi:10.1038/s41467-018-05499-5

Abstract

The optical selection rules in epitaxial quantum dots are strongly influenced by the orientation of their natural quantization axis, which is usually parallel to the growth direction. This configuration is well suited for vertically emitting devices, but not for planar photonic circuits because of the poorly controlled orientation of the transition dipoles in the growth plane. Here we show that the quantization axis of gallium arsenide dots can be flipped into the growth plane via moderate in-plane uniaxial stress. By using piezoelectric strain-actuators featuring strain amplification, we study the evolution of the selection rules and excitonic fine structure in a regime, in which quantum confinement can be regarded as a perturbation compared to strain in determining the symmetry-properties of the system. The experimental and computational results suggest that uniaxial stress may be the right tool to obtain quantum-light sources with ideally oriented transition dipoles and enhanced oscillator strengths for integrated quantum photonics.

Highlights

The optical selection rules in epitaxial quantum dots are strongly influenced by the orientation of their natural quantization axis, which is usually parallel to the growth direction
Different from most previous experiments, in which stress was added after growth as a perturbation to fine tune the emission properties of QDs25,26, confinement can be seen here as a perturbation compared to the strain-induced effects in determining the orientation of the quantization axis and the optical selection rules and excitonic fine structure
We focus on the experimental proof that uniaxial tensile stress along the [100] (x) direction leads to a holes’ ground-state (HGS) with HHx character, manifesting in characteristic optical selection rules

Summary

Introduction

The optical selection rules in epitaxial quantum dots are strongly influenced by the orientation of their natural quantization axis, which is usually parallel to the growth direction This configuration is well suited for vertically emitting devices, but not for planar photonic circuits because of the poorly controlled orientation of the transition dipoles in the growth plane. We show how the natural quantization axis of a QD can be turned to lie in the growth plane without rotating the semiconductor matrix, preserving the compatibility of the QD heterostructure with planar photonic processing To this aim, we use two key ingredients: (1) high-quality, initially unstrained GaAs QDs22–24 with a relatively large height, see Fig. 1a; (2) in-plane uniaxial stress, provided by micro-machined piezoelectric actuators featuring geometric strain amplification. Different from most previous experiments, in which stress was added after growth as a perturbation to fine tune the emission properties of QDs25,26, confinement can be seen here as a perturbation compared to the strain-induced effects in determining the orientation of the quantization axis and the optical selection rules and excitonic fine structure

Methods

Results

Conclusion