Two-dimensional MgP3 monolayer with remarkably tunable bandgap and enhanced visible-light and UV optical absorptions
Graphical abstract
Introduction
Two-dimensional (2D) materials have received extensive attention since the discovery of graphene due to their unique properties and huge promising applications [[1], [2], [3]]. 2D materials have been reported with many remarkable properties, for example, high carrier mobility, large specific surface area, and insulating topology [4]. For example, the 2D phosphorus has an adjustable bandgap under strain engineering [5]. Additionally, the phosphorene monolayer demonstrates several novel electronic properties [[6], [7], [8], [9], [10]] containing the satisfactory bandgap of 1.51 eV and the high hole mobility close to 2.6 × 104 cm2V−1s−1 [10]. The self-assembled monolayers(SAM) have been widely used in field-effect transistors [11]. For example, the field-effect transistor has been successfully manufactured with few-layer black phosphorus [9,[12], [13], [14]], and the hole mobility is as high as 5.2 × 103 cm2V−1s−1 while the drain current modulation can reach 105 [9,14]. The potential applications of monolayer materials in the photovoltaic fields were also reported. In 2018, Haq et al. [15] investigated the different phases of SnSe and found that the single-layer honeycomb polymorphs SnSe is very suitable for photovoltaic applications. Recently, Ali et al. [16] have summarized the SAM's applications in the interface engineering of perovskite solar cells to enhance stability and efficiency. Lei et al. [17] discovered a new PdSe2 monolayer with anisotropic and large carrier mobility could be used as a photovoltaic material. The narrow bandgap monolayer and SAM can also be used as thermoelectric materials. Park et al. [18] made a comprehensive review on the SAM's thermal conductance. In fact, many investigations for the thermoelectric properties of monolayers are reported recently. For example, the potential thermoelectric applications of lead-chalcogenide monolayers at room temperature are explored by Haq et al. [19] 2D materials can have a wide range of applications in the fields of electronics and optical devices. Therefore, the electronic and optical properties of 2D materials have been studied extensively. For example, Singh et al. [20] reported the optical and electronic properties of ThO2, UO2, and PuO2. Singh et al. [21] and Bhuyan et al. [22] studied the optical and electronic properties of several monolayers.
Recently, a series of studies on the properties of 2D triphosphides have been carried out, and many interesting results have been reported. In 2017, the 2D GeP3 monolayer is reported by Jing et al. [23]. The largest carrier mobility of the monolayer is 8.84 × 103 cm2 V−1 s−1, and the optical absorption in the visible-light range is apparent. Lu et al. [24] found that the CaP3 monolayer with a direct bandgap of 1.15 eV and ultrahigh carrier mobility. Very recently, the BiP3 [25] and AlP3 [26] monolayers are found to be excellent electronic and optical properties, and they can be used as potential photocatalysts for hydrogen evolution reaction under strains. Therefore, XP3 monolayers have become a monolayer family with various novel optoelectronic properties.
In this paper, inspired by the discovery of 2D CaP3 monolayer by Lu et al. [24], we suggest a triphosphate monolayer of MgP3 with the P1 space group as a new part of the XP3 monolayer family. The geometrical structure of the MgP3 monolayer is constructed and relaxed according to that of the CaP3 monolayer, and the stability is confirmed by the phonon dispersion with density functional perturbation theory and the structural and energy evolutions with ab initio molecular dynamics simulation(AIMD). By utilizing the first-principles density functional theory(DFT) with hybrid functional(HSE06) [27,28], we investigate the electronic and optical properties. The results show that the MgP3 monolayer possesses a direct 1.18 eV bandgap and can be remarkably changed by strain engineering. Meanwhile, the apparent optical absorption in ultra-violet(UV) and visible light range and anisotropic carrier mobilities are also observed. The strain engineering can apparently impact the conduction band edge, the bandgap value, and the optical absorption. The remarkably tunable bandgap and enhanced visible and UV light absorption imply that the MgP3 monolayer could be used as a promising candidate for photovoltaic, solar energy harvesting, and optoelectronic devices or materials.
Section snippets
Computational method
The electronic properties are calculated by employing the DFT method with plane-wave basis sets, which is completed with the Vienna ab initio simulation package (VASP 6.1.2) code [29,30]. In the geometrical optimization, the generalized gradient approximation based on the Perdew–Burke–Ernzerh of parameterization (PBE) is taken up to describe the electron interactions with exchange-correlation functional [27]. The electronic properties and optical absorption are obtained with the aid of the
Geometry and stability of the MgP3 monolayer
The fully optimized geometrical structure of the MgP3 monolayer with the P1 space group is shown in Fig. 1. The lattice parameters a and b are 5.59 and 5.71 Å, respectively. In the primitive cell, the red balls are Mg atoms and the blue ones are P atoms. The Mg atoms are six coordinated (six Mg–P bonds), there are two types of P atoms, one type is four coordinated (four P–P bonds), and the other type is four coordinated (two P–P bonds and two Mg–P bonds). As shown in Fig. S1, there is a small
Conclusion
The geometrical structure of the MgP3 monolayer with the P1 space group is identified on the basis of the first-principles calculations. The dynamical and the thermal stabilities of the newfound monolayer have been assured by employing the phonon dispersion and the AIMD simulation. The electronic properties, carrier mobility, and optical properties of the MgP3 monolayer are obtained with HSE06. A direct bandgap of 1.18 eV is identified for the newfound monolayer, and the carrier mobility of the
Author statement
Miao Liu: Data curation, Investigation, Writing-Original draft preparation. Chuan-Lu Yang: Conceptualization, Methodology, Supervision, Writing-Reviewing and Editing. Mei-Shan Wang: Visualization. Xiao-Guang Ma: Software.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. NSFC-11874192.
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