Ab initio study of BAs under pressure

Abstract

We use an ab initio total energy pseudopotential technique within the Density Functional Theory in the local-density approximation to determine the vibrational normal modes (phonons) defined within the first Brillouin Zone of BAs. We also study the effects of hydrostatic pressure on these phonons and the mode Grüneisen parameters using the response-function formalism for the computation. There is a very good agreement between the transversal optical phonon frequency at the Γ point calculated on this way and that with the frozen phonon technique. We also study the electronic band structure, the band-gap pressure dependence and the generalized stability criteria.1 Introduction A wide variety of physical properties of solids depends on their lattice-dynamical behaviour. Their understanding in terms of phonons is considered to be one of the most convincing pieces of evidence that our current quantum picture of solids is correct. Theoretical studies of structural and vibrational properties of materials are now routinely obtained by means of first principles calculations. The achievement of Density Functional Theory (DFT) and the development of a very efficient perturbative approach, the Density Functional Perturbation Theory (DFPT), even using the Local Density Approximation (LDA), make possible to obtain accurate phonon dispersions on a fine grid of wave vectors covering the entire Brillouin Zone.Boron compounds have attracted increasing research interest in the last few years. These materials are wide band gap semiconductors of technological interest, for potential optical and high temperature applications. The group of the zinc-blende boron compounds displays a peculiar behaviour when comparing with other semiconductors of the III-V family. Apparently their unusual properties are related with the absence of the p electrons in the core and the small core size of the B atom as shown by several studies [1 -4]. According to the Phillips van Vechten [5] scale BAs is the least ionic compound of the III -V family, f i = 0.002, so BAs is a boundary compound in the region that separates the ionic and covalent compounds.In a previous work [6], we had obtained the full set of first-order elastic constants of BAs, the bulk modulus, the optical phonon frequency at the Γ point, and the electronic band structure. In this work, we determine the pressure dependence of the electronic structure of BAs studying the main gaps behaviour under pressure. It is well known that DFT -LDA does not accurately describes the band gap, due to the well known underestimations of gaps. However, the pressure derivatives of conduction band states and their relative positions are given reasonably well within the DFT -LDA. By the other hand, we are also

How do electronic properties of conventional III–V semiconductors hold for the III–V boron bismuth BBi compound?

“…The conduction states Γ 1c and L 1c are the most sensitive to pressure. The pressure derivative coefficients of the Γ 1c states are close to the other III-V semiconductors [24] and to the boron compounds [25,26]. However, the pressure derivative coefficients of the X c states are much smaller than those observed in other semiconductors [24], but a similar behavior was found for boron compounds [25,26].…”

Pressure effects on the structural and electronic properties of ABX4 scintillating crystals

“…However, the boron anomaly in the FY diagram disappears if the second rule of the FY diagram is changed by the following: 2) A cation is always the cation with larger ionic radius (r A > r B ). In this case, all the compounds in the FY diagram basically remain at the same locations but the arsenate and phosphate compounds BAsO 4 and BPO 4 must be renamed to become "borates" AsBO 4 and PBO 4 because the radius of B is very small and leads boron to have the smaller coordination despite having smaller valence than As or P. This result is related to the reversal of the cation and anion role in BAs and BP recently reported and discussed in the literature[186,187]. Therefore, assuming that the compounds AsBO 4 and PBO 4 are not arsenates and phosphates but "borates", both compounds have k > 1 and the phase transition from high-cristobalite to quartz is compatible with the E rule in FY diagram.…”

Some physical properties of GaX (X=P, As and Sb) semiconductor compounds using higher-order perturbation theory

“…Due to technological importance of these materials it is essential to understand various properties of such semiconductor compounds and hence it is the current topic of interest for theoretical investigations as well as experimental research. It is also true that the interest of the research has increased on high-pressure behaviors of above materials [1][2][3][4][5][6].…”