Abstract
Hexagonal (2H) germanium is found to be a direct bandgap semiconductor, showing the potential of efficient light emission. Based on 2H–Ge, the structure and electronic properties of 2H–SiGe alloys are studied in detail by hybrid functional calculations. By varying the Si content of the 2H–SiGe alloys, the bandgap is found to be direct for Si contents smaller than 0.35. We find that the key factor in determining the indirect-to-direct transition of the band structures for 2H–SiGe alloys originates from the variation of lattice constant. Furthermore, the Si-rich 2H–SiGe alloy can be changed from indirect to direct bandgap by strain engineering. Furthermore, we consider the effective electron masses (me), band alignments with several oxides, optical absorption properties, and vacancy formation energies of 2H–SiGe alloys, which show that the direct-gap 2H–SiGe alloys have the potential for optoelectronic applications.
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