Origins of bandgap bowing character in the common-anion transition-metal-dichalcogenide ternary alloyed monolayer: ab initio investigation

• Published in: New journal of physics Vol. 23; no. 10; pp. 103027 - 103040
• Main Authors: Alfalasi, Wadha, Al Qasir, Iyad, Tit, Nacir
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.10.2021
• Subjects: Alloying; Alloys; Anions; bandgap bowing; Bowing; Cations; Chalcogenides; Chemical vapor deposition; Density functional theory; Energy gap; Graphene; Inventors; Molecular beam epitaxy; Molecular orbitals; Monolayers; Nanotechnology devices; Origins; Photoluminescence; photonic nano-devices; Physics; Symmetry; Ternary alloys; Transition metal alloys; Transition metals; transition-metal di-chalcogenide alloys
• ISSN: 1367-2630; 1367-2630
• DOI: 10.1088/1367-2630/ac2d73

Density functional theory is employed to investigate the origins of bandgap bowing character in transition-metal-dichalcogenide ternary alloyed monolayers (TMD-MLs). The available experimental photoluminescence (PL) data in literature have confirmed the existence of bowing character in the common-anion ternary alloys (e.g. Mo1−x W x S2) and its complete absence in the common-cation ternary alloys (e.g. MoS2(1−x)Se2x ). Our theoretical modeling of bandgap energy versus alloy composition, \({E}_{\text{g}}\left(x\right)\), in these respective alloys have yielded trends and bowing parameters in excellent agreement with the available PL data (i.e. B = 0.26 eV and zero, respectively). Calculated band structures showed that the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) states in TMD-ML to be fully attributed to the metal atoms and to follow the symmetry of the irreducible representations A 1′ (singlet \({d}_{{z}^{2}}\) state) and E′ (doublet of \({d}_{{x}^{2}-{y}^{2}}\) and d xy states) of the point group D 3h , respectively. Consequently, in case of common-cation TMD-ML alloys, \({E}_{\text{g}}\left(x\right)\) is linear and the bowing is absent. Whereas, in case of common-anion TMD-ML alloys, \({E}_{\text{g}}\left(x\right)\) is quadratic and the bowing is present because of the existence of competition between the cations (i.e. metal atoms) in contributing to HOMO/LUMO states. Our theoretical findings are corroborated with the available experimental data and have direct impact in TMD-based photonic nano-device applications.