You are cordially invited to the IPB COLLOQUIUM which will be held on Thursday, 25 December 2025 at 14:00 in the “Zvonko Marić” lecture hall of the Institute of Physics Belgrade. The talk entitled

GaN-Based Single-Photon Sources and Their Potential for Quantum Key Distribution

will be given by Žarko Gačević (Technical University of Madrid, Madrid, Spain). The abstract of the talk:

For more than two decades, the quest for practical, stable, and scalable single-photon sources has been at the forefront of quantum photonics research. While numerous material platforms, such as quantum dots, color centers, and two-dimensional materials, have demonstrated promising performance, many still face limitations including cryogenic operation, spectral instability, or technological incompatibility with established semiconductor processes. In this context, the III-nitride material system, and GaN in particular, has recently emerged as a highly compelling candidate for SPS technologies thanks to its robustness, wide bandgap, mature industrial ecosystem, and compatibility with visible and telecom-wavelength emission.

This colloquium reviews the current state of semiconductor single-photon sources, highlighting recent advances achieved in the development of InGaN/GaN nanowire–based emitters grown by molecular beam epitaxy at ISOM-UPM [1–3]. These nanostructures naturally host localized quantum emitters capable of producing antibunched light with good stability. The talk will highlight the underlying physical mechanisms leading to single-photon generation, the role of nanoscale composition and strain fluctuations, and the fabrication strategies to improve control of emitter formation. Building on this quantum-light platform, the seminar will then introduce the principles of quantum key distribution, focusing on hybrid time-bin/phase encoding architecture for fiber-based communication. Together, these developments illustrate a coherent path toward single photon driven photonic quantum technologies.

[1] Ž. Gačević, N. Vukmirović, N. García-Lepetit, A. Torres-Pardo, M. Müller, S. Metzner, S. Albert, A. Bengoechea-Encabo, F. Bertram, P. Veit, J. Christen, J. M. González-Calbet, and E. Calleja, “Influence of composition, strain, and electric field anisotropy on different emission colors and recombination dynamics from InGaN nanodisks in pencil-like GaN nanowires”, Phys. Rev. B 93, 125436 (2016).
[2] Ž. Gačević, M. Holmes, E. Chernysheva, M. Müller, A. Torres-Pardo, P. Veit, F. Bertram, J. Christen, J. M. González-Calbet, Y. Arakawa, E. Calleja, and S. Lazić, “Emission of linearly polarized single photons from quantum dots contained in nonpolar, semipolar, and polar sections of pencil-like InGaN/GaN nanowires”, ACS Photonics 4, 657–664 (2017).
[3] J. Obradović, M. Tinoco, L. Monge Bartolomé, V. J. Gómez Hernández, A. Torres-Pardo, S. Fernández-Garrido, Á. de Guzmán, and Ž. Gačević, “Formation mechanisms of (In,Ga)N nanoshells conformally grown around pencil-like GaN nanowires”, Cryst. Growth Des. (2026, accepted for publication).

The visit of Prof. Žarko Gačević is supported by the Science Fund of the Republic of Serbia, Grant No. 226, Development of GaN Nanowire Based Quantum Light Emitters – PhotonGaN.