Naomie Messudom | Searcharxiv

arXiv2025

Graphene assisted III-V epitaxy towards substrate recycling

Re-using the substrate is identified as a method for reducing the cost of high efficiency III-V solar cells. The approach investigated here consists in inserting a graphene layer onto a (001)GaAs substrate prior to the epitaxial growth of GaAs. To obtain a monocrystalline GaAs grown layer, the graphene layer is patterned, followed by a two-step epitaxial growth, here performed by molecular beam epitaxy (MBE). The first step is a selective area growth of GaAs in graphene openings, followed by a lateral overgrowth, under a modulated Ga flux. The second step, after reaching coalescence, consists in a regular growth under continuous Ga supply. It is observed that the pattern orientations relative to the crystallographic direction of the GaAs substrate below the graphene have an influence on GaAs morphology and quality. The best result was obtained for patterns oriented along [1__10]+22.5{\textdegree} with a graphene coverage of 50%, with a significantly reduced roughness down to 3.3 nm.

cond-mat.mtrl-sci↗

arXiv2025

Growth of Highly Conductive PtSe2 Films Controlled by Raman Metrics for High-Frequency Photodetectors and Optoelectronic Mixers at 1.55 {\mu}m

Two-dimensional PtSe2 exhibits outstanding intrinsic properties such as high carrier mobility, tunable bandgap, broadband absorption and air stability, making it ideal for (opto)electronic applications. In particular, thick PtSe2 is semimetallic and well suited for ultrafast optoelectronics in the infrared domain. However, achieving PtSe2 films of high crystalline quality with controlled properties on low-cost and insulating substrates remains challenging. Here, highly crystalline semimetallic PtSe2 films are grown by molecular beam epitaxy on sapphire substrates. It is shown how an optimized post-growth annealing remarkably improves the out-of-plane crystallinity and leads to record sheet conductances, up to 1.6 mS. In-depth structural analyses reveal the strong influence of the domain arrangement within the films on their electrical properties. Films that are mainly composed of vertically single crystalline domains exhibit high sheet conductance (1.1 - 1.6 mS), whereas films that contain superimposed twisted domains present low sheet conductance (0.5 - 0.6 mS). Moreover, it is demonstrated that the A1g Raman peak width, in addition to the commonly used Eg peak width, are both effective metrics for evaluating the quality of PtSe2: films with narrower Eg and A1g peaks exhibit higher in-plane and out-of-plane crystalline quality, respectively, as well as higher sheet conductance. Finally, coplanar waveguides integrating a semimetallic PtSe2 channel are fabricated on a 2-inch sapphire substrate to demonstrate optoelectronic devices operating at the 1.55 {\mu}m telecom wavelength. This includes photodetectors with a record 60 GHz bandwidth and the first PtSe2-based optoelectronic mixer with a bandwidth above 30 GHz.

cond-mat.mtrl-sci↗