Abstract
Newly discovered cubic phase of Germanium monochalcogenide (pi-GeS and pi-GeSe) with a moderate bandgap, less toxicity, and novel electronic properties have earned significant attention of researchers due to appropriate nature for the energy-related applications such as photovoltaic, optoelectronic and thermoelectric devices. The structural, electronic (band structure and DOS), optical and elastic properties of pi-GeS and pi-GeSe have been studied by ultrasoft pseudopotential technique. The band structure calculations confirm that both pi-GeS and pi-GeSe are indirect in nature with bandgap energies 1.38 and 1.04 eV respectively. The first-time calculated elastic constants of pi-GeS and pi-GeSe satisfy their mechanical stability criteria (Born stability). The elastic moduli (bulk, Young's, shear), Lame's parameters, Poisson's ratio, Debye temperature, and average sound velocity are determined by Voigt-Reuss-Hill approximation. The shear and Young's elastic properties reveal that both pi-GeS and pi-GeSe are anisotropic, which is also confirmed from 2D and 3D surface visualization. The calculated Debye temperature (theta(D)) of pi-GeS and pi-GeSe are 262.28 K and 264.46 K at 300 K, respectively. Additionally, the longitudinal and transversal waves sound velocities are calculated for the first time in [1 1 1], [1 1 0] and [1 0 0] directions. The present results reveal that n-GeS and n-GeSe could be appropriate candidates for exploitation in energy storage, optoelectronic and thermoelectric devices. Particularly GeS, which has higher absorption peaks and optimum bandgap (1.38 eV) for practical photovoltaic and photo-sensing applications. The present work provides the pathways for theoretical and experimental studies on electronic devices based upon cubic chalcogenides.