Structural, mechanical and electronic properties of two-dimensional single-layer hexagonal structures in the (1 1 1) crystal plane of IIIAs-ZnS systems (III = B, Ga and In) are studied by first-principles calculations based on density functional theory (DFT). Elastic and phonon dispersion relation display that 2D h-IIIAs systems (III = B, Ga and In) are both mechanical and dynamically stable. Electronic structures analysis show that the semiconducting nature of the 3D-IIIAs compounds is retained by their 2D single layer counterpart. Furthermore, density of states reveals the influence of σ and π bonding in the most stable geometry (planar or buckled) for 2D h-IIIAs systems. Calculations of elastic constants show that the Young's modulus, bulk modulus and shear modulus decrease for 2D h-IIIAs binary compounds as we move down on the group of elements of the periodic table. In addition, as the bond length between the neighboring cation-anion atoms increases, the 2D h-IIIAs binary compounds display less stiffness and more plasticity. Our findings can be used to understand the contribution of the σ and π bonding in the most stable geometry (planar o buckled) for 2D h-IIIAs systems. Structural and electronic properties of h-IIIAs systems as a function of the number of layers have been also studied. It is shown that h-BAs keeps its planar geometry while both h-GAs and h-InAs retained their buckled ones obtained by their single layers. Bilayer h-IIIAs present the same bandgap nature of their counterpart in 3D. As the number of layers increase from 2 to 4, the bandgap width for layered h-IIIAs decreases until they become semimetal or metal. Interestingly, these results are different to those found for layered h-GaN. The results presented in this study for single and few-layer h-IIIAs structures could give some physical insights for further theoretical and experimental studies of 2D h-IIIV-like systems.
Abstract-In this paper, we carried out first-principles calculations in order to investigate the structural and electronic properties of the binary compound gallium antimonide (GaSb). This theoretical study was carried out using the Density Functional Theory within the plane-wave pseudopotential method. The effects of exchange and correlation (XC) were treated using the functional Local Density Approximation (LDA), generalized gradient approximation (GGA): Perdew-Burke-Ernzerhof (PBE), Perdew-Burke-Ernzerhof revised for solids (PBEsol), Perdew-Wang91 (PW91), revised Perdew-Burke-Ernzerhof (rPBE), Armiento-Mattson 2005 (AM05) and meta-generalized gradient approximation (meta-GGA): Tao-Perdew-Staroverov-Scuseria (TPSS) and revised Tao-Perdew-Staroverov-Scuseria (RTPSS) and modified Becke-Johnson (MBJ). We calculated the densities of state (DOS) and band structure with different XC potentials identified and compared them with the theoretical and experimental results reported in the literature. It was discovered that functional: LDA, PBEsol, AM05 and RTPSS provide the best results to calculate the lattice parameters (a) and bulk modulus (B 0 ); while for the cohesive energy (E coh ), functional: AM05, RTPSS and PW91 are closer to the values obtained experimentally. The MBJ, Rtpss and AM05 values found for the band gap energy is slightly underestimated with those values reported experimentally.
Based on density functional theory, first-principles calculations were performed in order to study the titanium incorporation on polar and nonpolar GaN surfaces. The formation energy calculations indicate that Ti impurity atoms prefer to incorporate in surface layers (first and second) of GaN. It is also concluded that the incorporation of Ti atoms in Ga-substitutional sites are more energetically favorable compared with N-substitutional or interstitial sites on the polar and nonpolar GaN surfaces. For Tirich growth conditions, formation energy calculations show the formation of TixN layers on the a and c GaN surfaces, which corroborates recent experimental observations. Results also display that the 3d-Ti states are the responsible for the metallization of the surface on the c and m planes, forming an intermetallic alloy (TixN), which could be used as low-resistance ohmic contacts for GaN. In addition, the magnetic properties with Ti doping show magnetization of about 1.0 μB/Ti atom for the nonpolar GaN surfaces.
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