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Saransh Raj GOSAIN presents

Room temperature single photon source for integrated photonics

Monday, 13th December 2021 at 10:00 am

Room D420, Nevill Mott, Institut Néel, CNRS : number of person limited to 25


For those who wish to be physically  present the number of people will be restricted. You have to send an email to edith.bellet-amalric@cea.fr with the following information:

SURNAME NAME COMPANY EMAIL  I need a CNRS entrance (yes/no)


For those of you who cannot be physically present, it will be possible to follow the defense through a live stream on Zoom :



The defence will be in English.


Abstract :

Single-photons are promising for applications such as in quantum computing, quantum metrology, or quantum communication where they can be used as flying-qubits. Challenges faced in single-photon-based technologies are efficient light extraction, scalability and high temperature operability. CdSe quantum dots (QD) have shown promise for single-photon emission up to room temperatures in the visible range (∼550 nm), a spectral range useful for free-space communication. To tackle light extraction and scalability issues, we propose a system where a CdSe QD is embedded in a ZnSe tapered nanowire (NW), realized with Molecular beam epitaxy (MBE). A tapered NW shape is targeted to efficiently extract light from the QD-NW system in free-space. Moreover, this QD-NW system is a single unit that can be picked up and transferred from one substrate to another.

In this thesis work, finite-element-method numerical simulations were performed to optimize the shape and size of our QD-NWs for efficient light collection along the NW axis. The growth of gold catalysed CdSe/ZnSe QD-NWs by MBE,under vapor-solid-solid growth mechanism, was studied. and optimized to control the radial and axial growth of the NWs. Reproducible growth of vertically oriented CdSe-ZnSe QD-NWs (QD diameter ~6 nm, height ~4 nm) with a tapered Zn(Mg)Se shell (NW diameter ~100nm, NW length ~ 2-4 µm ) was achieved. The emission properties of these QD-NWs was studied from cryogenic to room temperatures with continuous and pulse excitation. It is shown that even when single-photon emission is confirmed with anti-bunching measurements under continuous excitation, it does not confirm that the emitter can emit single-photons on-demand under pulsed excitation. For QD-NWs grown with optimized parameters, single-photon emission was achieved up to room temperature. Finally, prospects for evanescent coupling of QD-NW to silicon nitride waveguides for integrated photonics applications are discussed.

Thesis director : Kuntheak Kheng (CEA, IRIG, PHELIQS)
Co-director : Edith-Bellet Amalric (CEA, IRIG, PHELIQS)

Jury’s Members :
M. Nicolas Chauvin (rapporteur, Chargé de Recherche, Institut des Nanotechnologies de Lyon, École centrale de Lyon)
M. Vincent Sallet (rapporteur, Chargé de Recherche, Groupe d’étude de la matière condensée, Université Paris-Saclay)
M. Thierry Baron (examinateur, Directeur de Recherche, Laboratoire des Technologies de la Microélectronique, Université Grenoble Alpes)
Mme. Valia VOLIOTIS (examinatrice, Professeur des universités, Institut des NanoSciences de Paris, Sorbonne Université)