Job title:
Post-doctorat (M/F) synthèse de matériaux métastables et caractérisations electro-optiques
Company:
Job description
Offer Description—-ContextControlling the crystal polytypism (i.e. difference in the stacking sequence of the building layer) is an emerging pathway to modify material properties and create on demand new functionalities. Most semiconductors, like Si, Ge and GaAs, crystallize in the cubic (3C) structure, but they may also be stabilized with a polytype stacking with hexagonal symmetry (2H and 4H). Specifically, the reduction of crystal symmetry strongly modifies the electronic band structure. It occurs to be a valuable mean of electronic band engineering. In particular, the hexagonal 2H and 4H structures of Ge exhibit a direct band gap and efficient light emission capabilities [1]. These materials hold the promise of photonic functionality compatible with the silicon technology. Quantum dots (QD) of hex-Ge would be particularly well suited for single photon source.
In defiance to crystal energetics considerations, hexagonal metastable phases can be stabilized by using well-adapted growth kinetics[2]. Until now, the controlled growth of hexagonal metastable GaAs has been only realized using vapor-liquid-solid growth in the form of III-V nanowires. Recently, we have achieved a disruptive epitaxy of planar layers of hexagonal metastable of GaAs. This breakthrough makes possible a full characterisation of hexagonal GaAs. Besides, this hexagonal GaAs thin layer is used as a template for integration and design of hexagonal Si(1-x)Gex for light emission.[1] E. Fadaly et al. Nature 2020, 580, 205-209 doi: 10.1038/s41586-020-2150-y
[2] L. Vincent et al., Adv. Materials Interfaces 9, 2102340 (2022)Objectives
GaAs thin films with the wurtzite (2H) as well as the 4H stacking sequence are deposited by heteroepitaxy on adequate and oriented substrates, using UHV-VPE. The first objective is to improve the crystalline quality of the layers by optimizing substrate surface preparation and growth conditions. The challenge is to maintain the hexagonal structure during growth with reduced defect density. A special attention will be paid on the formation and nature of stacking faults that would lead the material to turn to cubic structure. The quantification of the hexagonality yield will require experimental developments based on cross-correlation of structural characterizations.
These hexagonal GaAs layers will be fully characterized with standard electrical and optical characterizations to achieve a comprehensive investigation of the potential of this material. The hexagonal stacking displays significant anisotropic features, thin films will provide opportunity to explore nonlinear properties.
Besides, we intend to develop the epitaxy of thin layers and quantum dots of hexagonal Si(1-x)Gex with well controlled compositions and sizes to demonstrate enhanced light emission.Work plan and skill training
The selected candidate will perform cutting-edge fundamental research in material science by contributing to:
– improve the crystalline quality of metastable GaAs (2H and 4H) thin films with UHV-VPE by optimising the growth parameters (substrate preparation, growth temperature, precursor flow)- structural characterisations to identify the nature of defects, reduce their density, evaluate the hexagonality yield and study the stability of the metastable phases
– investigate the electro-optical properties with various standard characterization methods (ellipsometry, photoluminescence, cathodoluminescence, electroluminescence, Raman spectroscopy, I(V), C(V), EBIC, hall effect…) to assess the refractive index, the charge carrier concentration, the identification of optically active defects… The impact of I3 defects on optical properties is an open question that should will be addressed. Complementary techniques (IR absorption, SNOM) can be implemented, in collaboration with our partners in SOLEIL synchrotron
– develop the growth of Si(1-x)Gex on hexagonal GaAs template.The position is in the SEEDs group from Material department in Center of Nanosciance and Nanotechnologies. Visit our website
The Centre de Nanosciences et de Nanotechnologies (C2N- ) is a joint research unit between the CNRS and Université Paris-Saclay developping research in the field of material science, nanophotonics, nanoelectronics, nanobiotechnologies and microsystems, as well as in nanotechnologies. The center hosts one of the cleanroom in France dedicated to micro and nanofabrication processes, growth, epitaxy and characterization.
SEEDs team has a long-standing know-how in synthesis and characterisation of group-IV and III-V semiconductor. At the moment we are especially investigating different ways to synthesized metastable hexagonal phase of such materials.
Among growth facilities our group hold an original cluster tool currently used for the epitaxial growth of III-IV-V materials in the form of semiconducting 2D and 3D structures, quantum wells, quantum dots, nanowires… It is fully compatible with 4″ or possibly 8″ substrates and comprises two UHV-VPE chambers fed with hydrides (silane, germane, digermane, diluted diborane and phosphine) or metal organic precursors (TMGa, TBAs…), a third chamber is equipped with surface analysis probes, i.e. AES (Auger Electron Spectroscopy) and XPS (X-ray photoelectron spectroscopy). RHEED technique is used for monitoring the epitaxial growth in real time.Where to apply WebsiteRequirementsResearch Field Physics Education Level PhD or equivalentLanguages FRENCH Level BasicResearch Field Physics Years of Research Experience NoneAdditional InformationEligibility criteriaProfile and skills required
We are looking for applicants with a PhD in physics, physical chemistry, material science solid state physics or related areas with an interest in nanotechnologies.
The candidate should have:
-expertise in growth processes
– strong knowledge in crystallography and crystal defects as well as interest in crystal growth
– strong knowledge in semiconductor physics
– ability to work in a cleanroom environment
– ability to work in a team and good communication skills
– upper intermediate level in English (minimum B2)Additional comments—-
RAS Website for additional job detailsWork Location(s)Number of offers available 1 Company/Institute Centre de Nanosciences et de Nanotechnologies Country France City PALAISEAU GeofieldContact CityPALAISEAU WebsiteSTATUS: EXPIREDShare this page
Expected salary
Location
Palaiseau, Essonne
Job date
Thu, 02 Jan 2025 07:14:04 GMT
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