Buried Stressor Engineering for Position-Controlled InGaAs Quantum Dots with Local Density Variation for Integrated Quantum Photonics

Abstract

We report on the monolithic, two-step epitaxial growth of site-controlled InGaAs quantum dots via the buried stressor method with local quantum dot density variation. As a result of high fabrication accuracy, we achieve low lateral displacements of the individual buried stressor apertures of $ 17^{+19}_{-17}$~nm from mesa centers. We provide extensive micro-photoluminescence and cathodoluminescence characterization of the site-controlled quantum dots and give theoretical calculations, explaining the effect of the stressor aperture on the quantum dot emission properties, positioning, and density. We show reproducibility of the nucleation process for apertures of the same size and achieve precisely-positioned, low- and high-density quantum dot nucleation within one active layer growth step. The results presented in this work demonstrate the significant potential of the buried stressor concept in fabricating single photonic chips, simultaneously combining single-photon sources and microlasers featuring different local densities of site-controlled quantum dots, paving the way for highly functional source modules with applications in photonic quantum technology.

Figures (6)

• Figure 1: Schematics of the sample fabrication. a) Layer design and illustration of the ICP-RIE step to uncover the AlAs layer. b) Illustration of the in-situ lateral oxidation of the AlAs layer which results in change of the surface strain profile. c) CLSM images showing oxide apertures, where the different aperture sizes can be observed for smaller (bottom) and larger (top) mesa. d) Self-aligned defect which can be resolved on the surface via AFM.
• Figure 2: CLSM investigation of stressor apertures. a) Mean aperture sizes for individual mesa sizes are fitted with linear functions. b) Absolute aperture offset from the mesa center showing very low aperture displacement. Panels c) and d) show the histograms aperture offsets on sample center and edge, respectively.
• Figure 3: $\mu$--PL investigation of the QD emission and theoretical calculations of the biaxial strain. Panels a), b), and c) depict the mean QD emission wavelength, the mean integrated QD emission area, and the mean number of QD peaks, respectively. The highlighted regions show the maximum values. d) Selected spectra for various mesa sizes from a single patterned edge field. e) Continuum elasticity theory calculation of the biaxial surface strain profile for different aperture sizes. f) Calculated exciton wavelength shift with respect to the applied biaxial. All QD spectra were excited with a tunable pulsed laser at 890 nm. The excitation power was kept constant at 1.5 $\mu$W.
• Figure 4: A comparison of measured and simulated FSS. a) FSS dependency on the aperture size, measured from low-density spectra of the SCQDs. b) Calculated FSS values for QDs with dimensions of $20\times20\times2$ nm$^{3}$ and $34\times34\times3$ nm$^{3}$. The abbreviation ME in b) refers to the use of the multipole expansion of the exchange interaction in our calculations Takagahara2000Krapek2015. The slight cusps and dips in the dependencies in b) are due to numerical errors in the calculations.
• Figure 5: SCQD investigation via CL mapping. a) Selected CL intensity profiles taken on and off the aperture. The insets show the corresponding SEM images overlaid with respective CL maps, for aperture sizes of 0.54 $\mu$m (20.8 $\mu$m mesa) and 1.08 $\mu$m (21.3 $\mu$m mesa). Panel b) SEM images overlaid with their respective CL maps for increasing aperture sizes. c) Dependency of the CL-measured QD displacement (red), CL-measured emission center (blue), and the simulated positions of the tensile strain maxima (green) for increasing aperture sizes.