Why Chemical Vapor Deposition Grown MoS2 Samples Outperform Physical Vapor Deposition Samples: Time-Domain ab Initio Analysis.

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) have drawn strong attention due to their unique properties and diverse applications. However, TMD performance depends strongly on material quality and defect morphology. Experiments show that samples grown by chemical vapor deposition (CVD) outperform those obtained by physical vapor deposition (PVD). Experiments also show that CVD samples exhibit vacancy defects, while antisite defects are frequently observed in PVD samples. Our time-domain ab initio study demonstrates that both antisites and vacancies accelerate trapping and nonradiative recombination of charge carriers, but antisites are much more detrimental than vacancies. Antisites create deep traps for both electrons and holes, reducing energy gaps for recombination, while vacancies trap primarily holes. Antisites also perturb band-edge states, creating significant overlap with the trap states. In comparison, vacancy defects overlap much less with the band-edge states. Finally, antisites can create pairs of electron and hole traps close to the Fermi energy, allowing trapping by thermal activation from the ground state and strongly contributing to charge scattering. As a result, antisites accelerate charge recombination by more than a factor of 8, while vacancies enhance the recombination by less than a factor of 2. Our simulations demonstrate a general principle that missing atoms are significantly more benign than misplaced atoms, such as antisites and adatoms. The study rationalizes the existing experimental data, provides theoretical insights into the diverse behavior of different classes of defects, and generates guidelines for defect engineering to achieve high-performance electronic, optoelectronic, and solar-cell devices.