Scientific project:

The photovoltaic technology is largely dominated by silicon devices (≈ 90% of the market), which present very limited progress margins today, with an efficiency intrinsically limited below 30%. It is largely agreed that the next device generation will combine several materials, beyond silicon alone. We are developing an innovating technology, to produce solar cells based on III-V materials, already presenting high efficiencies (up to 46% under concentration), with significant cost reductions.

Our strategy is to recycle the III-V substrates, which represent the largest device cost share, for several epitaxial growths. To do so, we are developing innovative processes to modify the substrate surface, so that the fabricated layers can be easily detached, leaving a surface compatible with subsequent growths. A promising route recently suggested consist in transferring a graphene layer before performing the epitaxy, as displayed in the attached file. I was shown that the graphene permits the fabrication of a monocrystalline material, while allowing its exfoliation. Developing this method requires exploring fundamental physical phenomena as well as defining practical methodologies.

The intern will work on the development of the process as well as on the characterization of the obtained structures and intermediate products. He / she will propose further developments of the techniques already existing at the laboratory, as well as suggest the exploration of new methods. He / she will propose models to explain the observed phenomena, and design experiments for their validation. To complete those tasks, the intern will use his own knowledge as well as the scientific literature. The intern will take advantage of a unique collection of fabrication and characterization methods (XPS, TEM, SEM, luminescence) available in partner laboratories. This environment will provide various opportunities to tackle this project challenge and gain experience.

Profile:

The candidate must possess solid knowledges in material physics, characterization, and fabrication processes in a clean room environment. He / she must show good project management skills, for the development of technological procedures involving numerous parameters. He / she will be able to work independently and suggest innovative solutions to reach the project objectives. Collaborative work being at the core of the program, communication skills are required for team working as well as regular presentation of work progress in internal meetings.

Starting date: from 01/02/2025 (adjustable)

Duration: 6 months

This internship can be followed by a PhD.

Websites: https://sunlit-team.eu

poursuite en thèse envisageable

Internship proposal for a second-year master student Synthesis of quantum dots in III-V nanowires
Duration : 6 months starting from March
Salary ~ 600 EUR/month
Supervisor : Federico PANCIERA
Laboratory : Centre for Nanoscience and Nanotechnology (C2N), U. Paris-Saclay/CNRS
Web: https://elphyse.c2n.universite-paris-saclay.fr/en/

Contacts:

federico.panciera@c2n.upsaclay.fr

Context of the project : 

Semiconductor nanowires (NWs) exhibit unique properties that make them potential building blocks for a variety of next generation devices such as biosensors, solar cells, transistors, quantum light sources and lasers. In order to take advantage of the physical properties of NWs, it is crucial to control their geometry, crystal structure and doping. This goal will ultimately be achieved by a deep understanding of the growth mechanisms. The most common growth technique is the vapor-liquid-solid (VLS) method, where a liquid metal droplet catalyzes the growth of a solid NW from gas phase precursors. In this growth mode, the droplet plays a fundamental role in determining the structure of the nanowire, and the remarkable range of structures enabled by VLS can be thought of as the result of engineered changes to the droplet.
For example, growth of III-V semiconductor NWs using the VLS method can result in crystal structures different from their bulk phase. In GaAs NWs stable zincblende (ZB) phase coexists with metastable wurtzite (WZ) structure resulting in NWs having a mixed-phase structure. Remarkably, the valence and conduction bands of the two phases are misaligned so that small sections of one phase within the other effectively confine charge carriers.
Controlled switching between the two phases enables the synthesis of novel heterostructures, crystal-phase quantum dots (CPQD), with exceptional properties and potential applications in photonics [1] and quantum computing [2,3]. In contrast to compositional heterojunctions, CPQDs have intrinsically abrupt interfaces and
hence do not suffer from alloy intermixing at the interface, which hampers precise control of the electronic properties in compositional heterostructures.