Wet-Etched Microlens Array for 200 nm Spatial Isolation of Epitaxial Single QDs and 80 nm Broadband Enhancement of Their Quantum Light Extraction.

Shulun Li,Xiangbin Su,Haiqiao Ni,Xiangjun Shang,Zhichuan Niu,Yu Zhang,Huiming Hao,Yao Chen,Hanqing Liu

doi:10.3390/nano11051136

Abstract

Uniform arrays of three shapes (, , and ) of GaAs microlenses (MLs) by wet-etching are demonstrated, ∼200 nm spatial isolation of epitaxial single QDs embedded (: 890–990 nm) and broadband ( nm) enhancement of their quantum light extraction are obtained, which is also suitable for telecom-band epitaxial QDs. Combined with the bottom distributed Bragg reflector, the -shaped ML forms a cavity and achieves the best enhancement: extraction efficiency of 26%, Purcell factor of 2 and single-photon count rate of counts per second at the first lens; while the -shaped ML shows a broader band (e.g., longer ) enhancement. In the MLs, single QDs with featured exciton emissions are observed, whose time correlations prove single-photon emission with multi-photon probability ; some QDs show both biexciton and exciton X emissions and exhibit a perfect cascade feature. This work could pave a step towards a scalable array of QD single-photon sources and the application of QD photon-pair emission for entanglement experiments.

Highlights

5.5 kcps with the average I f lat of 4 kcps, while the intensity of quantum dots (QDs) in the MLs varies from 20 kcps to 110 kcps at maximum
Its statistical distribution is a good reflection of the QD X-position variation from the ML center as the simulation in Figure 2a reflects: the maximal intensity corresponds to a QD in the ML center that has very few statistical counts, while the minimal intensity (∼20 kcps) with many statistical counts corresponds to a QD
Region where single QD is observed in a ML and in the multi-QD region where multi-QDs are observed, especially in a hat-shaped ML

Summary

Introduction

Semiconductor quantum dots (QDs) is a promising candidate for realization of on-demand quantum light source with high photon extraction efficiency, strong suppression of multi-photons and high indistinguishability of the emitted photons [6]

Methods

Results

Conclusion