Structural and optical properties of position-retrievable low-density GaAs droplet epitaxial quantum dots for application to single photon sources with plasmonic optical coupling

Abstract

The position of a single GaAs quantum dot (QD), which is optically active, grown by low-density droplet epitaxy (DE) (approximately 4 QDs/μm(2)), was directly observed on the surface of a 45-nm-thick Al0.3Ga0.7As capping layer. The thin thickness of AlGaAs capping layer is useful for single photon sources with plasmonic optical coupling. A micro-photoluminescence for GaAs DE QDs has shown exciton/biexciton behavior in the range of 1.654 to 1.657 eV. The direct observation of positions of low-density GaAs DE QDs would be advantageous for mass fabrication of devices that use a single QD, such as single photon sources.

Keywords: Droplet epitaxy; GaAs; Micro-photoluminescence; Quantum dot; Single photon.

Figure 1

Schematics of structures, AFM image, and the PL peaks of low-density GaAs DE QDs. (a) Schematics of structures of low-density GaAs DE QDs as a function of thickness of HT-Al0.3Ga0.7As (2, 25, 50, 85 nm), (b) AFM image (3 μm × 3 μm) of low-density GaAs DE QDs (approximately 4 QDs/μm²) on Al0.3Ga0.7As/GaAs substrate, and (c) macro-PL (log scale) and (d) μ-PL (exciton, biexciton peaks) spectra of low-density GaAs DE QDs with 105-nm capping at low temperature (12 ~ 16 K).

Figure 2

AFM images (3 μm × 3 μm) of a surface. (a) 22-nm, (b) 45-nm, and (c) 70-nm-thick Al_0.3Ga_0.7As capping for low-density GaAs DE QDs.

Figure 3

Macro-PL and SEM image. (a) Macro-PL (log scale) of low-density GaAs DE QDs with 22- and 45-nm cap at low temperature (12 K). The PL intensity was normalized with PL peak intensity of GaAs-related peak band around 830 nm. (b) SEM image (x300,000) of low-density GaAs DE QDs with 45-nm AlGaAs capping layer. The inset of Figure 3b is magnified by four for one QD.