Seminar: Elizaveta Semenova (DTU)
Epitaxy of InAs/InP quantum dots and deterministic device fabrication for quantum photonic applications in the telecom C-band
E. Semenova, DTU Electro, Technical University of Denmark, Kgs. Lyngby
Deterministic sources of single photons or entangled photon pairs operating in the telecom C-band are highly desired for various quantum applications, including quantum key distribution, quantum sensing and distributed quantum computing. The interest is motivated by the potential integration of these sources with the well-developed Si quantum photonics platforms and the existing fibre-based telecommunication infrastructure. Photon emission from quantum dots (QDs) in the telecom C-band wavelength range could be achieved either from the GaAs material system by applying the metamorphic growth approach [1, 2] or by using the InP -based material system [3].
In this talk, we focus on the InP-based material system and will discuss epitaxial methods of InAs QD synthesis: (i) Stranski-Krastanov growth mode and (ii) droplet epitaxy. By altering the growth parameters, we tailor the QD system properties to satisfy the strict requirements for quantum photonic applications [4]. We discuss in detail the growth methods as well as the morphological, electronic, and optical properties of the resulting InAs/InP QDs [5-7].
Further, I will present an experimental realization of a deterministically fabricated QD-based single photon source operating in the telecom C-band: an InAs/InP QD weakly coupled to a circular Bragg grating cavity. To overcome the issue of high noise of the camera sensors operating at the telecom wavelength range, we guide the QD emission out-of-plane to increase the photon collection. This is done by implementing a metallic mirror underneath the InP slab containing QDs [7]. Then, to address individual QDs, we apply photoluminescence far-field imaging. We thus localize and map hundreds of QDs and define their positions with respect to alignment marks. Then, we fabricate spectrally-matched circular Bragg grating photonic cavities with a numerically optimized design. The fabrication flow enables cavity placement with a spatial precision of <90 nm with respect to the QD position and with a total process yield of ~ 30 %.
The resulting devices demonstrate weak coupling between QDs and the cavity mode, verified with a Purcell enhancement factor ∼ 5. The photon extraction efficiency at the collection lens with NA = 0.4 is estimated to be 16.6 ± 2.7 %, and we measure the purity of g (2)(0) = (3.2±0.6) × 10−3 of triggered single-photon emission. Photon indistinguishability associated is evidences via two-photon interference with a visibility up to V = (19.3±2.6) % and VPS= % without and with temporal postselection, respectively [8]. Our results are encouraging for the realization of deterministic photonic devices in the telecom C-band, for delivery of single photons or on-chip quantum information processing.
[1] E. S. Semenova et al, J. Appl. Phys., 103, 103533 (2008)
[2] S. L. Portalupi et, al, Semicond. Sci. Technol. 34, 053001 (2019)
[3] N. Carlsson et al, J. Cryst Growth 191, 347 (1998)
[4] Y. Berdnikov et al, arXiv:2301.11008 (2023)
[5] P. Holewa et al, PRB, 101, 19, 195304 (2020)
[6] P. Holewa et al, Nanophotonics, 11(8), 1515-1526 (2022)
[7] P. Holewa et al, ACS Photon. 9, 2273– 2279 (2022)
[8] P. Holewa et al, arXiv:2304.02515 (2023)