Germanium-based quantum emitters towards a time-reordering entanglement scheme with degenerate exciton and biexciton states

Nicola Dotti, Francesco Sarti, Sergio Bietti, Alexander Azarov, Andrej Kuznetsov, Francesco Biccari, Anna Vinattieri, Stefano Sanguinetti, Marco Abbarchi, and Massimo Gurioli

Phys. Rev. B 91, 205316 – Published 29 May 2015

Abstract

We address the radiative emission of individual germanium extrinsic centers in ${Al}_{0.3} {Ga}_{0.7} As$ epilayers grown on germanium substrates. Microphotoluminescence experiments demonstrate the capability of high temperature emission (70 K) and complex exciton configurations (neutral exciton $X$ and biexciton $X X$ , positive $X^{+}$ and negative $X^{-}$ charged excitons) of these quantum emitters. Finally, we investigate the renormalization of each energy level showing a large and systematic change of the binding energy of $X X$ and $X^{+}$ from positive to negative values (from $\sim + 5$ meV up to $\sim - 7$ meV covering $\sim 70$ meV of the emission energy) with increasing quantum confinement. These light emitters, grown on a silicon substrate, may exhibit energy-degenerate $X$ and $X X$ energy levels. Furthermore, they emit at the highest detection efficiency window of Si-based single-photon detectors. These features render them a promising device platform for the generation of entangled photons in the time-reordering scheme.

Received 16 January 2015
Revised 7 May 2015

DOI:https://doi.org/10.1103/PhysRevB.91.205316

Authors & Affiliations

Nicola Dotti¹, Francesco Sarti¹, Sergio Bietti², Alexander Azarov³, Andrej Kuznetsov³, Francesco Biccari¹, Anna Vinattieri¹, Stefano Sanguinetti², Marco Abbarchi^4,*, and Massimo Gurioli^1,*

¹LENS, Dipartimento di Fisica, Università di Firenze, Via Sansone 1, I-50019 Sesto Fiorentino, Italy
²L-NESS and Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Via Cozzi 53, I-20125 Milano, Italy
³Department of Physics, University of Oslo, NO-0316 Oslo, Norway
⁴CNRS, Aix-Marseille Université, Centrale Marseille, IM2NP, UMR 7334, Campus de St. Jérôme, 13397 Marseille, France

^*Corresponding authors: marco.abbarchi@im2np.fr; gurioli@fi.infn.it

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Issue

Vol. 91, Iss. 20 — 15 May 2015

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Images

Figure 1
(a) Bottom: Sketch of the sample composition: 5 nm GaAs (capping layer), 200 nm ${Al}_{0.3} {Ga}_{0.7} As$ (active layer), 650 nm GaAs (buffer layer), Ge (substrate). Top: Scheme of the optical apparatus used for PL experiments. (b) SIMS measurements on the investigated sample. Ge (left axis, calibrated), Ga and Al (right axis, not calibrated) ions concentration are plotted in a logarithmic scale as a function of the milled depth. Shaded areas highlight the different layers.
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Figure 2
(a)–(c) Top panel shows a 1D scan over $100 μ m$ (in $0.5 μ m$ steps) on samples GaAs $400^{\circ} C$ , GaAs $580^{\circ} C$ , and Ge $580^{\circ} C$ . The white dashed line highlights the spatial position of the spectrum shown in the corresponding bottom panel. Bottom panels: Typical PL spectrum extracted from the 1D scan in the top panel.
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Figure 3
(a) Typical PL spectrum from the sample Ge $580^{\circ} C$ . The shaded areas I, II, and III highlight the spectral intervals used to represent the spectral map shown in (b). (b) $50 \times 50 μ m^{2}$ spectral map integrated on the three different spectral intervals I, II, and III highlighted in (a). The excitation power density was $P_{0} = 5 \times 10^{2} W / {cm}^{2}$ . Similar maps but with a sharper spectral filtering are shown as an animated map in the Supplemental Material [80, 81]. In the left panel I four spots (i, ii, iii, and iv) are highlighted and the corresponding extracted spectra are shown in (c). (d) Top panel: Integrated and normalized emission from Ge centers. Central panel: Same as top panel but for Ge-centers-free areas (i.e., “bulk” ${Al}_{0.3} {Ga}_{0.7} As$ ). Bottom panel: Isolated Ge-centers emission obtained as intensity difference between the two spectra in the top and middle panels. The continuous red line is a Gaussian fit to the data.
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Figure 4
(a) Series of PL spectra at different excitation power of an individual Ge impurity exhibiting $X^{-}, X X$ , and $X$ recombination. (b) Summary of the PL intensity as a function of the excitation power $P$ of the data reported in (a). Symbols are the experimental data while the lines represent Poissonian fit. (c) Polarization map of an individual Ge impurity exhibiting $X X, X$ , and $X^{+}$ recombination. (d) $X, X X$ , and $X^{+}$ normalized and energy-shifted emission at 10 K. The continuous lines are Gaussian fit to the data. (e) Normalized spectra of $X^{+}$ emission at 10 and 70 K. The zero-phonon-line (ZPL) and the polaron emission are highlighted.
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Figure 5
(a) Scheme of $X$ and $X X$ energy levels for three different binding energies of $X X$ ; from left to right: positive, zero, and negative. V and H highlight the linear polarization of the emitted photons. (b) Binding energy of $X^{-}, X^{+}$ , and $X X$ . Dotted lines are guides to the eyes.
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