Strain-dependent electronic and optical properties of boron-phosphide and germanium-carbide hetero-bilayer: A first-principles study

Opto-electronic properties of boron phosphide–germanium carbide (BP/GeC), a new van der Walls hetero-bilayer (HBL) with all possible stacking patterns, are studied under the density functional theory originated first-principles. The dynamical and chemical stabilities of the hetero-bilayer are confirmed by phonon spectra and binding energy. Among the dynamically stable HBLs, HBL 1 has the lowest binding energy with the smallest interlayer spacing of about 3.442 Å. Both values and natures (indirect or direct) of the electronic band structure are highly responsive to the stacking patterns. We have found that HBL 1 is indirect, while HBL 2 and HBL 3 become a direct bandgap at the K high symmetry point. All HBLs show type-II band alignment. Both compressive and tensile biaxial strains on the electronic properties of HBLs have been considered. All the HBLs become a direct bandgap for the compressive strain at 4% and 6%. We have also presented the optical property calculations on the HBLs, namely, the complex dielectric function and absorption properties, showing unique optical properties with significant absorption (5 × 105 cm−1 in HBL 2) in the whole solar spectra compared with their comprising monolayers. Moreover, the strain-dependent optical absorption coefficients with varying photon wavelengths are calculated and the maximum value is attained to be about 6.5 × 105 cm−1 in HBL 2 at 4% compressive strain. Consequently, the optoelectronic properties we have explored in our proposed new hetero-bilayer systems can guide the experimental realization of the hetero-bilayers and effective use in the future photovoltaic applications.