PhD Defense: Jordi Roubichou

“Study of new types of detectors in the extended SWIR: extending the operating band beyond 1.7 µm”

The defence will take place on Thursday, 19 March 2026 at 2:00 pm, at the Laboratoire d’Astrophysique de Marseille (LAM), Aix-Marseille Université. The presentation will be given in French.

Jury :

– Angela VASANELLI (MPQ, Université Paris Cité) — Reviewer
– Jean-Philippe PEREZ (IES, Université de Montpellier) — Reviewer
– Guilaine LAGACHE (LAM, AMU) — Chair
– Olivier SAINT-PÉ (Airbus Defence & Space, Toulouse) — Examiner
– David BARATE (DGA, Paris) — Examiner
– Didier TIPHENE (LIRA, Observatoire de Paris) — Examiner
– Jean-Luc BEUZIT (LAM, CNRS) — Supervisor
– Jean-Luc GACH (FLI) — Co-supervisor
– Jean-Luc REVERCHON (III-V Lab) — Invited member
– Vincent GUERIAUX (Thales LAS) — Invited member

Summary : 

The extended short-wave infrared (eSWIR) lies at a singular spectral position at the interface between the visible and thermal infrared domains, and is of major interest for defence, security, space, and astronomy. This spectral band combines sensitivity to reflected luminance and thermal emission, thereby influencing scene contrast and the information content of images, including in environments degraded by fog, smoke, or pollution. It enables both night-time imaging without artificial illumination through the nightglow phenomenon and active imaging relying on suitable illumination sources. In space and astronomy applications, the eSWIR constitutes a key spectral band, ranging from Earth observation and optical communications to imaging and spectroscopy in the J, H, and K bands, as well as the study of specific astrophysical objects. Beyond these applications, the eSWIR is also well suited to a wide range of civil and industrial uses, including environmental and agricultural monitoring, multispectral imaging, spectroscopy, and gas detection.

In the conventional SWIR (Short-Wave Infrared) range, InGaAs photodiodes grown on InP substrates represent the reference technology, with a cutoff wavelength limited to 1.7 µm, while historical technologies based on II–VI materials, such as HgCdTe, provide broader spectral coverage at the expense of increased operational constraints, higher technological complexity, and elevated fabrication costs. In recent years, an emerging trend in infrared detection has focused on the use of III–V superlattices, artificial materials composed of nanometre-scale layer stacks whose effective bandgap can be tailored through band engineering. This approach enables extended cutoff wavelengths while offering higher operating temperatures, less restrictive growth processes, and reduced cost compared with II–VI technologies.

In this context, an approach based on strain-balanced type-II InGaAs/GaAsSb superlattices grown on InP substrates is being developed by Thales at the III–V Lab, in collaboration with the Laboratoire d’Astrophysique de Marseille. The work presented provides a comprehensive analysis of these solutions, from modelling to the evaluation of standalone photodiodes and focal-plane arrays. Device performances in terms of quantum efficiency, dark current, absorption, minority-carrier lifetime, and collection length are investigated for several superlattice architectures, together with simulations based on a k·p model. The results obtained at the photodiode level are finally compared with those measured at the focal-plane level, in order to assess the impact of the observed phenomena on operability, signal-to-noise ratio, response uniformity, and spatial resolution. Altogether, this work aims to provide a comprehensive analysis, from modelling to photodiode characterisation and focal-plane evaluation, in order to highlight the strengths and limitations of eSWIR InGaAs/GaAsSb superlattice photodetectors.