Discovering the desirable physical properties of arsenic compounds AB 2 As 2 and their alloys: a theoretical study.

In the current study, the stability, elastic, electronic, and optical properties of AB 2 As 2 (A = Ca, Sr; B = Mg, Zn, Cd) and their alloys with a trigonal CaAl 2 Si 2 -type structure are thoroughly examined for the first time based on the first-principles calculations. The optimized structural parameters are highly consistent with the experimental data. The dynamic stability of four alloys is demonstrated by computing their phonon spectra. All compounds are mechanically stable and brittle materials. The results imply that both CaMg2As2 and SrMg2As2 exhibit indirect band gaps at the Γ - M symmetry point, while AZn 2 As 2 and ACd 2 As 2 at the Γ point exhibit direct bandgap features. Moreover, the trend of band gap reduction (∼1 eV) is presented from AMg 2 As 2 to ACd 2 As 2 . The allowed transition from an indirect band gap to a direct band gap is observed from AMg 2 As 2 to A(Mg 0.5 B 0.5 ) 2 As 2 . Four alloys display more suitable direct band gaps (1.2-1.5 eV) for potential optoelectronic applications. In addition, these compounds possess high carrier mobility. The analysis of various optical properties is discussed in detail. This finding demonstrates that some novel compounds can be potential candidates for possible optoelectronic devices.