Band Gap of Semiconducting High Pressure Phase of Boron

Abstract

The partially ionic high pressure phase of boron γ-B28 was synthesized at 12 GPa 1500oC using a multi-anvil press. The crystal structure of γ-B28 was confirmed by x-ray diffraction. The γ-B28 phase is metastable at ambient condition. Upon grinding, the sample back transform to α-B12 phase. Optical absorption was conducted to investigate the γ-B28 sample. The optical absorption edge was observed at a wavelength of 725nm indicating a band gap of 1.7 eV for this semiconducting high pressure phase, in a good agreement with theoretical calculation (1.5-1.7 eV).