First-principles study on tunable optoelectronic properties of monolayer Mo1-xWxSe2 alloys and defect engineered electronic properties of Mo1-xWxSe2 alloys

When two lattice-matched nanoparticles with different band gaps, namely MoSe2 and WSe2, are alloyed to construct a ternary compound, the resulting mixture exhibits interesting changes in dynamic stability, electronic, and optoelectronic features. Subsequently, by introducing single Se vacancy in Mo1-xWxSe2 alloys, dynamic stability and electronic properties of the alloys are modulated. In this work, we conducted first-principles calculations based on density-functional theory (DFT) to evaluate the tunable stability and physical properties of two dimensional monolayer Mo1-xWxSe2 and defective Mo1-xWxSe2 for different alloy compositions. Our investigation discloses that the direct band gap in these alloys could be modulated with nonlinear dependency on composition. On the other hand, band gap reduced significantly for every composition in defective Mo1-xWxSe2 alloy and chalcogen vacancies induced non-zero density of states (DOS) within the band gap. These defects change the structure of the valence and conduction band and therefore the significant increase in effective mass which results in a reduction in mobility. The other electronic parameters were gradually tuned by varying composition in pure and defected alloys including DOS, charge densities, charge accumulation, mobility, and effective mass. Pure and defective Mo1-xWxSe2 alloys were energetically and dynamically stable. Furthermore, the high optical absorption of the alloys can be utilized in optoelectronic devices. The findings of this work revealed the tunability of the physical properties of Mo1-xWxSe2 and defective Mo1-xWxSe2 by alloying and will be beneficial to design nanoscale electronic and optoelectronic devices with enhanced performance.