Study of the Phase Transition and Physical Properties of AlAs, ScAs and Al_xSc_1-XAs Compounds by the FP-LMTO Method

In this present work, we will study the physical properties of a brand new semiconductor material. the structural stability and the electronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) semiconductors as well as their ternary alloys (Al_xSc_1-xAs, 0≤ x≤1) in both rocksalt RS (B1) and zincblende ZB (B3). Calculations on both structures are done the method (FPLMTO, Full Potential Linear Muffin Tin). In the framework of density functional theory (DFT). The exchange-correlation potential was calculated using both the Local Density Approximation and the Generalized Gradient Approximation.

The structural parameters of Al_xSc_1-xAs alloys, such as the lattice constant, the bulk module and its derivative are calculated. The lattice parameter deviates slightly from the line of Vegard’s Law in B3 structure, while the deviation was more pronounced in B1 structure.

The calculations showed a phase transition from the ZnS phase (B3) to the RS phase (B1) at pressures (7, 10.5, 14.0 and 23.0 Gpa in LDA and (10.0, 12.5, 10.0 and 25.0 GPa) in GGA for x = 0.25, 0.50, 0.75 and 1.00) respectively.The calculated electronic properties showed that in phase B1, there exists an energy band (X-X) with a direct gap at x = 0.00. On the other hand, in phase B3, there are two kinds of energy bands, of direct gap (Γ-Γ) for x = 0.25, 075 and 1.00, the second band is of indirect gap (Γ-X) for x = 0.50, suggesting the possibility to be used in the long wavelength optoelectronic applications. The deviation of The calculated band gap deviation from linear behavior was significant in both structures. The Al_xSc_1-xAs alloys were found to be semiconducting at x=0 in the B1 phase and at x=0.25, 0.50, 0.75 and 1 in the B3 phase. Concerning calculations of the optical properties of the ternary Al_xSc_1-xAs alloy at concentrations x= 0.25, 0.50 and 0.75 in the ZnS (B3) phase, and from our bibliographic research we are sure that no reference exists in the literature. Our work can therefore be used as a reference for future research. Our simulation results are in good agreement with those obtained theoretically and experimentally.