Robust indirect band gap and anisotropy of optical absorption in B-doped phosphorene

Abstract

A traditional doping technique plays an important role in the band structure engineering of two-dimensional nanostructures. Since electron interaction is changed by doping, the optical and electrochemical properties could also be significantly tuned. In this study, density functional theory calculations have been employed to explore the structural stability, and electronic and optical properties of B-doped phosphorene. The results show that all B-doped phosphorenes are stable with a relatively low binding energy. Of particular interest is that these B-doped systems exhibit an indirect band gap, which is distinct from the direct one of pure phosphorene. Despite the different concentrations and configurations of B dopants, such indirect band gaps are robust. The screened hybrid density functional HSE06 predicts that the band gap of B-doped phosphorene is slightly smaller than that of pure phosphorene. Spatial charge distributions at the valence band maximum (VBM) and the conduction band minimum (CBM) are analyzed to understand the features of an indirect band gap. By comparison with pure phosphorene, B-doped phosphorenes exhibit strong anisotropy and intensity of optical absorption. Moreover, B dopants could enhance the stability of Li adsorption on phosphorene with less sacrifice of the Li diffusion rate. Our results suggest that B-doping is an effective way of tuning the band gap, enhancing the intensity of optical absorption and improving the performances of Li adsorption, which could promote potential applications in novel optical devices and lithium-ion batteries.

Borophosphene: A New Anisotropic Dirac Cone Monolayer with a High Fermi Velocity and a Unique Self-Doping Feature

“…Thus, this layer exhibits orthogonal symmetry with two B atoms and two P atoms in a unit cell. The calculated lattice constants a and b are 3.22 and 5.57 Å, respectively, which are very close to those of the h -BP monolayer. − The B–B, P–P, and B–P bond lengths (see Table ) are comparable to those of the h -BP monolayer (B–P, 1.86 Å), borophene (B–B, 1.62 Å), and phosphorene (P–P, 2.22 Å), , indicating that the chemical bonds in the borophosphene are strong. Cohesive energy is one of the key factors for evaluating the feasibility of experimental synthesis for the predicted 2D materials, − which is calculated according to the formula E c = ( E B + E P – E BP )/2, where E B , E P , and E BP are the total energies of a single B atom, a single P atom, and one BP molecule in the borophosphene, respectively.…”

“…The calculated lattice constants a and b are 3.22 and 5.57 Å, which are very close to those of h-BP monolayer. [42][43][44][45] The bond lengths of B-B, P-P and B-P (see Table 1) are comparable to those of 5 h-BP monolayer (B-P: 1.86 Å), 45 borophene (B-B: 1.62 Å), 46 and phosphorene (P-P: 2.22 Å), 47,48 indicating that the chemical bonds in the borophosphene are strong. Cohesive energy is one of the key factors to evaluate the feasibility of experimental synthesis for the predicted 2D materials, [49][50][51] which is calculated according to the formula of In order to evaluate the stability of borophosphene, phonon spectrum with density of state (DOS) is calculated and shown in Figure 1b.…”

Shining Light on New-Generation Two-Dimensional Materials from a Computational Viewpoint

“…Most importantly, it exhibits strong optical anisotropic nature along armchair and zigzag directions (see Figure c), which remain intact after chemically doping the system . Wu et al have shown boron-doped phosphorene to absorb more intensely in the lower energy range (low light absorption in these systems is observed between 0 and 3.0 eV in the zigzag direction, which is absent in the pure phosphorene) than pure phosphorene due the presence of a boron-dominated impurity band or charge transfer (CT) state in this modified system . Fortunately, recent experimental developments are now able to realize and testify to the computational calculations.…”

“…Interestingly, other newly emerged 2D materials such as phosphorene (i.e., in this case, single-layer black phosphorus) exhibits a much smaller optical gap of 1.22 eV in the G 0 W 0 +BSE level of theory, a bit lower than the experimental one (1.88 eV) . Most importantly, it exhibits strong optical anisotropic nature along armchair and zigzag directions (see Figure c), which remain intact after chemically doping the system . Wu et al have shown boron-doped phosphorene to absorb more intensely in the lower energy range (low light absorption in these systems is observed between 0 and 3.0 eV in the zigzag direction, which is absent in the pure phosphorene) than pure phosphorene due the presence of a boron-dominated impurity band or charge transfer (CT) state in this modified system .…”

“…(b) Optical absorption spectra of g-C 3 N 4 nanoflakes after physicochemical modifications calculated by TDDFT with HSE06 (reprinted with permission from ref ; Copyright 2017 American Chemical Society), showing a huge range of absorption wavelength. (c) Optical absorption spectra of pure and B-doped phosphorene along armchair and zigzag directions at the PBE-GGA level (reprinted with permission from ref ; Copyright 2017 Royal Society of Chemistry). (d) Optical conductivity of germanene, antimonene, and their heterostructures at the PBE-GGA level (reprinted with permission from ref ; Copyright 2016 Royal Society of Chemistry).…”