Thèse Operando Ultrafast Spectroscopy Of Colloidal Nanocrystal Electroluminescent Devices Toward Efficient Laser Diodes H/F

École polytechnique

Établissement : École polytechnique
École doctorale : Ecole Doctorale de l'Institut Polytechnique de Paris
Laboratoire de recherche : PMC - Laboratoire de Physique de la Matière Condensée
Direction de la thèse : Thierry GACOIN ORCID 0000000167743181
Début de la thèse : 2026-10-01
Date limite de candidature : 2026-04-30T23:59:59

Colloidal nanocrystals, or quantum dots, are semiconductor nanoparticles grown in solution using wet chemistry approaches. Those materials can be used as optical gain media for the development of a new class of lasers, compatible with virtually any substrate. Optically excited lasing has been well demonstrated with QDs from UV to the infrared, but applications for integrated technologies require laser diodes, where the material is excited by electrical pulses rather than optical ones. However, the material behavior under high intensity excitation required to reach the optical gain regime is still poorly understood. The goal of this PhD is to build a new tool for investigation of optical gain properties in operando conditions, that is devices under electrical operation. The candidate will participate to the construction of a new hybrid optical/electrical spectroscopy setup dedicated to these studies. He will then build electroluminescent devices from visible-emitting quantum dots, and use operando spectroscopy to measure population inversion dynamics and understand the key barriers to efficient optical gain under electrical excitation. The candidate will then, using this tool, explore new device architecture and operating parameters aiming at maximizing the gain performance, to obtain way to access electrically-injected gain in a QD device and toward a true QD laser diode.
Context:
Colloidal quantum dots (CQDs) are nanoparticles of semiconductor that, due to their size (2-20 nm), fall in the quantum confinement regime. As such, these materials exhibit optical properties that can be continuously adjusted over a wide range of wavelengths, from the infrared to the ultraviolet. CQDs are already used in next-generation displays (Samsung QLED), infrared sensors (ST Microelectronics, IMEC) and as bio-tagging materials. The next step for these materials is the democratization of their use as a source of laser light, that requires the nanoparticles to sustain very high excitation levels. The process of stimulated emission, responsible for emission of coherent laser light, is a collective process that requires nanocrystals to be packed together tightly, typically in solid state films. The solution processability of nanocrystals makes them a great candidate for on-chip integrated photonics, where integration of light sources remains complex due to the constraints of epitaxy. Recently, the proof-of-concept for an electrical CQD device capable of emitting light in the optical gain regime (ie, able to reach the population inversion regime and of amplifying light) have been demonstrated. In order to go forward, there is now a need for a deeper understanding of transport and carrier dynamics in the high electrical injection regime, and especially of quantifying optical gain under electrical excitation.

Colloidal quantum dots (CQDs) are nanoparticles of semiconductor that, due to their size (2-20 nm), fall in the quantum confinement regime. As such, these materials exhibit optical properties that can be continuously adjusted over a wide range of wavelengths, from the infrared to the ultraviolet. CQDs are already used in next-generation displays (Samsung QLED), infrared sensors (ST Microelectronics, IMEC) and as bio-tagging materials. The next step for these materials is the democratization of their use as a source of laser light, that requires the nanoparticles to sustain very high excitation levels. The process of stimulated emission, responsible for emission of coherent laser light, is a collective process that requires nanocrystals to be packed together tightly, typically in solid state films. The solution processability of nanocrystals makes them a great candidate for on-chip integrated photonics, where integration of light sources remains complex due to the constraints of epitaxy. Recently, the proof-of-concept for an electrical CQD device capable of emitting light in the optical gain regime (ie, able to reach the population inversion regime and of amplifying light) have been demonstrated. In order to go forward, there is now a need for a deeper understanding of transport and carrier dynamics in the high electrical injection regime, and especially of quantifying optical gain under electrical excitation.