Propriétés structurales, électroniques et optiques des monocouches GeS2, GeO2 et du Janus GeSO.

Abstract

This master’s thesis analyzes the structural, electronic, and optical properties of GeS2 , GeO2 , and Janus GeSO monolayers in their trigonal crystalline form. Calculations, performed within the framework of density functional theory (DFT) using the VASP code, employ the GGA-PBE and HSE06 approximations for the exchange-correlation potential, along with the DFT-D2 method to account for van der Waals interactions. After determining the structural parameters, the energetic and mechanical stability of the GeS2, GeO2 , and Janus GeSO monolayers was confirmed. The electronic properties reveal distinct semiconductor behaviors : GeS2 and GeO2 exhibit indirect bandgaps, while Janus GeSO has a direct bandgap, making it suitable for optoelectronic applications. The structural asymmetry of Janus GeSO induces a permanent electric dipole, enhanced by a specific orbital distribution between its faces, positioning it as a promising material for electronic engineering of 2D Janus structures. Optically, GeS2 shows strong absorbance in the visible and low-UV range, while GeO2 absorbs efficiently in the high-UV range. Janus GeSO, with versatile absorption covering the infrared, visible, and mid-UV ranges, complements these properties. This spectral complementarity positions these materials, particularly in heterostructures, for applications in multispectral photodetection and photovoltaic conversion. These theoretical results highlight the potential of 2D Janus materials for advanced optoelectronic and energy devices, pending experimental validation.