Electronic and optical properties of defective MoSe2 repaired by halogen atoms from first-principles study

Abstract

Using first-principles calculations, we have investigated the electronic and optical properties of MoSe2 with Se vacancies (SVSe, α-DVSe, and β-DVSe) and further repaired by halogen atoms (F, Cl, Br and I). For the MoSe2 with Se vacancies, Cl, Br and I atoms can occupy the Se vacancies and form three bonds with the neighboring Mo atoms, but F atom only can form two F-Mo bonds with the lowest adsorption energies due to its smaller atomic radius. Halogen atoms possess one more electron than Se atom, which results in a local magnetic moment of 1µB for single vacancy and 2µB for double vacancies. The MoSe2 with Se vacancies exhibits n-type doping semiconductor, which agrees well with the experimental observations. After halogen atoms doping in the defective site, the defective levels shift from electron donor levels to the electron acceptor levels, and finally reduces the n-type doping from the defective structure through a p-doping process. Compared to the defective MoSe2, absorption enhancement around low energy area of 0∼3 eV is observed in the halogen-repaired MoSe2 structures. Our results provide new insights in structural repairing of the transition metal dichalcogenides and promote their remarkable properties for applications in optoelectronics.

Nonstoichiometric Phases of Two-Dimensional Transition-Metal Dichalcogenides: From Chalcogen Vacancies to Pure Metal Membranes

“…If the sample is n-type doped, it may give rise to negative charge accumulation. The additional charge may also come from other defects created in MoSe 2 by the electron beam − or adsorption of impurities on these defects, which gives rise to the occupied or partially occupied defect-induced states in the gap.…”

Development of laser-combined scanning multiprobe spectroscopy and application to analysis of WSe2/MoSe2 in-plane heterostructure

“…In general, p-type characteristics are difficult to obtain for these materials, 23) and when Se atoms are desorbed, n-type characteristics are expected to be introduced. 24,25) Based on these results, Schottky barrier at MoSe 2 did not suppress the current compared with the barrier at the WSe 2 , possible band structures for the MoSe 2 (band gap: 1.6 eV) and WSe 2 (band gap: 1.7 eV) regions 26) with PtIr 5 coated tips are shown in Fig. 2(d).…”

Gate-Tunable Bound Exciton Manifolds in Monolayer MoSe2

“…Previous density functional theory (DFT) calculations showed that a monoselenium vacancy (V Se ) gives rise to two unoccupied degenerate states near the conduction band minimum (CBM) and one occupied state below the valence band maximum (VBM) in monolayer MoSe 2 . − It is worth noting that other defects such as a diselenium vacancy (V 2Se ) and a V Se pair (V Se –V Se ) also result in in-gap states, , but we focus on the effect of V Se due to its predominance (Figure S6). While chalcogen vacancies were previously thought to be responsible for the commonly observed n-type behavior in TMDs, there is increasing evidence that they are in fact deep acceptors (A). − Theory shows that V Se is stable in either neutral or negatively charged states: − that is, it can accept an electron to compensate the native n-doping.…”