Ab Initio Study Of Band Gap Properties In Metastable Bc8/St12 Sixge1-X Alloys

The cubic Ia (3) over bar (BC8) and tetragonal P4(3)2(1)2 (ST12) high pressure modifications of Si and Ge are attractive candidates for application in optoelectronic, thermoelectric, or plasmonic devices. SixGe1-x alloys in BC8/ST12 modifications could help overcome the indirect and narrow bandgaps of the pure phases and enable tailoring for specific use-cases. Such alloys have experimentally been found to be stable at ambient conditions after release from high pressure synthesis; however, their fundamental properties are not known. In this work, we employ ab initio calculations based on density functional theory (DFT) to investigate the electronic properties of these compounds as a function of composition x. We obtain the effective band structures of intermediate alloys by constructing special quasi-random structures (SQSs) and unfolding their band structure to the corresponding primitive cell. Furthermore, we show that the indirect bandgap of the ST12 Ge end-member can be tuned to become direct at x(Si) approximate to 0.16. Finally, our investigations also demonstrate that the BC8 modification, on the other hand, is insensitive to compositional changes and is a narrow direct bandgap semiconductor only for the case of pure Si. Published under license by AIP Publishing.