Plasma growth of GaAs-on-Si for cost-effective photovoltaic and photonic applications through A[...]

Organisation/Company Ecole polytechnique Department Physics Research Field Engineering » Precision engineering Physics » Crystal growth Researcher Profile First Stage Researcher (R1) Positions PhD Positions Application Deadline 10 Apr 2026 - 00:00 (Europe/Paris) Country France Type of Contract Temporary Job Status Full-time Hours Per Week 35 Offer Starting Date 4 Oct 2026 Is the job funded through the EU Research Framework Programme? Not funded by a EU programme Is the Job related to staff position within a Research Infrastructure? No

Offer Description

Research Theme / Context

III–V semiconductors, and GaAs in particular, hold world records in photovoltaic conversion efficiency and constitute the foundation of high-performance photonic devices. However, their large-scale deployment in terrestrial photovoltaics and integrated photonics remains limited by the high cost of substrates and by conventional high-temperature epitaxy techniques (typically above 600–650 °C), such as MBE and MOCVD. These approaches impose high thermal budgets, limit compatibility with low-cost silicon, and reduce precursor utilization efficiency, thereby constraining scalability. A key scientific challenge is therefore to enable high-quality GaAs growth directly on low-cost silicon substrates while drastically reducing process temperature. Successfully addressing this challenge would pave the way to high-efficiency GaAs/Si tandem solar cells and to affordable III–V-on-Si photonic devices. At LPICM, we aim to tackle this issue through the development of Remote Plasma Vapor Phase Epitaxy (RPVPE), a low-temperature plasma-based growth process in which reactive species are generated in the plasma phase rather than solely by thermal activation at the surface. Because plasma epitaxy involves a large number of strongly coupled parameters (plasma power, gas composition, pressure, substrate temperature, V/III ratio, doping flows), the optimization of GaAs/Si growth constitutes a highly multidimensional problem. In this context, AI and data-driven approaches offer a powerful framework to accelerate process optimization, identify correlations between growth conditions and material properties, and guide the design of optimized device architectures.

PhD Project Description

The PhD project aims at establishing a coherent GaAs/Si technological platform by combining low-temperature RPVPE growth, advanced characterization, device fabrication, and AI-based process optimization. The work will focus on the development of GaAs heteroepitaxy on Silicon and on engineered Ge/Si or SiGe virtual substrates. Growth parameters such as plasma power, pressure, temperature, and doping conditions will be systematically varied to build a structured experimental database. A comprehensive characterization methodology will be implemented to correlate growth conditions with material quality and device performance. Machine learning algorithms will be used to identify correlations between growth parameters and material quality, predict optimal growth conditions windows, and accelerate convergence toward low-defect GaAs layers. In parallel, AI-assisted optimization will be applied to device architecture design, helping to determine optimal thicknesses, doping levels ... Building on optimized material quality, the candidate will fabricate both GaAs/Si tandem solar cells integrating a GaAs top cell on a Silicon bottom cell. The targeted outcome is a proof-of-concept GaAs/Si tandem solar cell exceeding 25% efficiency while maintaining a reduced thermal budget. Beyond photovoltaics, the developed low-temperature GaAs/Si platform will be evaluated for photonic integration. Overall, this PhD aims to position low-temperature GaAs/Si integration as a disruptive approach, bridging high-efficiency photovoltaics and affordable silicon photonics within a unified, data-optimized materials framework.

Application

• A Master’s degree in Physics, Electrical Engineering, Materials Science, or a related field.
• Familiarity with semiconductor devices.
• Skills or interest in low-temperature plasmas, spectroscopy, and thin-film materials.
• Motivation for interdisciplinary work combining plasma, materials sciences, and device engineering.

Additional Information

Work Location(s)

Number of offers available 1 Company/Institute LPICM UMR7647- cnrs / ecole polytechnique Country France Geofield