Description du sujet de thèse

The impressive piezoelectric properties of ScAlN [1] have made it a very interesting semiconductor alloy for sensors and high-frequency filters based on acoustic waves. Furthermore, this alloy is promising for the fabrication of RF transistors [2]. Indeed, thanks to the large electric polarization induced at the interface of ScAlN/GaN heterostructures, electron gases with densities superior to 3E13/cm² can be generated even with ScAlN barrier thickness well below 10 nm. However, despite these impressive properties, the first demonstration of an RF HEMT (high electron mobility transistor) based on ScAlN was reported lately, in 2019. Since 2020, the epitaxy of the ScAlN alloy is studied at CRHEA and encouraging results have been obtained, including ScAlN/GaN heterostructures grown on silicon which is a substrate of choice for industry.

In this context, the TWINS project funded by the French National Research Agency (ANR) aims at combining a ScAlN/GaN HEMT with a surface acoustic wave (SAW) structure to achieve a variable frequency filter operating in the 3-10 GHz frequency range. In a first step, this totally novel approach will necessitate the optimization of the epitaxy, of the device process and the characterization of the two building blocks (transistor and SAW filter). In a second step, various integration routes will be studied to propose a device able to satisfy the 5G telecommunications requirements. For this purpose, the project gathers 3 academic laboratories: CRHEA, Institut Jean Lamour and IEMN.

Contexte de travail

The proposed Ph.D thesis perfectly fits with TWINS project and will consist in the molecular beam epitaxy of ScAlN alloy [3] and the characterization of ScAlN/GaN heterostructures. The main objective will be to correlate growth conditions and heterostructure parameters (alloy composition, thickness) with structural properties (roughness, crystal quality) and electrical properties (carrier density, mobility, electrical traps, piezoelectric response…). For this purpose, X-ray diffraction, atomic force microscopy (http://www.crhea.cnrs.fr/en/characterization.htm), test device process in the laboratory cleanroom (http://www.crhea.cnrs.fr/en/technology-platform.htm) and electrical characterizations (Hall effect, I-V and C-V measurements) will be performed. Once the growth and device process optimized, various approaches will be investigated to cointegrate the different parts of the variable frequency filter.
The study will be carried out at CRHEA (Université Côte d'Azur, CNRS, Valbonne, 06) in tight collaboration with partners laboratories. Knowledges in solid-state physics and materials science are necessary. Furthermore, the laboratory is protected by the restricted access regime (ZRR

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Knowledges in solid-state physics and materials science are necessary.

Communication of Master 1 and 2 transcripts in the application file