Description of the thesis topic

In the pursuit of advancing energy efficiency and enhancing the performance of electronic systems, this thesis focuses on developing a new technological platform for heterojunction bipolar transistors (HBTs) based on AlGaN/GaN, tailored for high-frequency (RF) applications. This innovative technology, still underexplored in France, leverages the expertise of the Anode group at IEMN, internationally recognized for its research on III-V HBTs and vertical GaN Schottky devices for high-frequency and THz applications. The primary goal is to meet the growing demands for energy efficiency and power density in strategic sectors such as telecommunications, automotive, and aerospace.
The objective is to explore the potential of GaN-based HBTs, a promising technology for high-frequency power applications. By combining the inherent advantages of HBTs (high transconductance, high power density, etc.) with the unique properties of GaN (wide bandgap, high critical electric field, and excellent thermal stability), this project aims to establish a technological foundation for vertical RF devices in AlGaN/GaN.The project will focus particularly on thin-collector structures optimized to achieve transition frequencies (fT) and maximum oscillation frequencies (fMax) between 50 and 90 GHz , while ensuring breakdown voltages above 100 V.
To achieve these objectives, the first step will involve a detailed study of charge injection mechanisms in the devices. The optimization of the emitter-base junction will be prioritized, with a focus on controlling the aluminum content in the AlGaN emitter layer. This phase will rely on advanced simulations using the SILVACO tool. Once these parameters are defined, the design of lithographic masks for transistor fabrication will follow.
The fabrication process will prioritize the optimization of ohmic contacts, particularly the base contact, to reduce specific contact resistance. Additionally, attention will be given to minimizing surface defects caused by critical dry etching steps, such as ICP etching. These improvements are essential to ensure high performance and enhanced reliability, especially for vertical device architectures.
In the final phase, the fabricated transistors will be subjected to detailed characterization to evaluate their RF and power performance, including load-pull measurements at 18 GHz and 40 GHz, depending on the frequency capabilities of the HBTs.
By combining structural engineering and advances in fabrication processes, this project aims to position AlGaN/GaN HBTs as a reference technology for next-generation vertical devices in high-frequency power applications.

Work Context

The work will be carried out within the ANODE (Advanced Nanometric Device) team at IEMN, which is specialized, among other things, in the development and characterization of very high-frequency components. THz applications are one of the group's specialties.
The activity will be primarily focused on cleanroom work but will also include measurements of the fabricated devices at the IEMN characterization center. Specific safety training related to cleanroom operations will be provided, along with an introduction to specialized technological techniques for utilizing available resources.
IEMN is a Joint Research Unit affiliated with CNRS, the University of Lille, the Polytechnic University of Hauts-de-France, Centrale Lille, and ISEN JUNIA. Its design, manufacturing, and characterization equipment ranks among the best in Europe. The institute comprises approximately 230 permanent members (professors, researchers, engineers, and administrative staff) and around 150 doctoral students. Research at IEMN spans a wide range of fields, from materials physics and nanostructures to telecommunications systems and acoustic and microwave instrumentation.

The position is located in a sector under the protection of scientific and technical potential (PPST), and therefore requires, in accordance with the regulations, that your arrival is authorized by the competent authority of the MESR.

Constraints and risks

Clean room.

Additional Information

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