Ab-initio DFT FP-LAPW GGA and LDA TB-mBJ and SO theoretical study of structural and elastic properties of Zinc-Blende crystal phase GaAs1−xBix alloys

We present an ab-initio theoretical study of structural and elastic properties of GaAs1−xBix alloys in the Zinc-Blende (ZB) phase. We use a recent version of Wien2k package code based on Density Functional Theory (DFT) Full Potential and Linearized Augmented Plane Waves (FP-LAPW) method including recent Tran-Blaha modified Becke-Johnson correction of the exchange potential (TB-mBJ) and the spin-orbit interaction (SO). The calculations are performed within the Local Density Approximation (LDA) as well as the Generalized Gradient Approximation (GGA). We study first the structural properties of GaAs1−xBix alloys by solving Murnaghan equation of state. Our results show that the ZB phase is the lowest equilibrium crystal structure of GaAs1−xBix in the whole alloy composition range, in agreement with previous theoretical predictions. The variations versus Bi contents of the ZB GaAs1−xBix lattice constant a0, bulk modulus B0 and its pressure derivative B0′ are also found very close to other theoretical and experimental data, but with much smaller bowing effects indicating a better resolution thanks to TB-mBJ correction. The variations of B0 versus the reverse equilibrium volume of the unit cell (1/V0) are found to be described by the simple linear empirical expression B0 = −0.21068 + 0.16695/V0 which is close to the theoretical prediction for III-V semiconductors with, however, somewhat lower linear coefficients values, suggesting a more metallic behavior. In a second part of this work, we use Birch-Murnaghan approach to study the elastic properties of GaAs1-xBix alloys. The elastic stiffness coefficients, C11, C12 and C44, and their variations versus alloy composition were determined for ZB GaAs1−xBix alloy. Their values in GaAs and GaBi binary compounds are found in very good agreement with available experimental and/or theoretical data. Their variations in GaAs1−xBix alloy show a monotonic decrease with increasing Bi contents, indicating a softening behavior as is typically the case for metallic alloys. The values of the bulk modulus derived with the help of C11, C12 and C44 elastic stiffness coefficients are found very close to B0 values derived directly from Murnaghan equation of state, indicating the good accuracy of Cij coefficients deduced from Birch-Murnaghan procedure.