title: Properties of the exotic metastable ST12 germanium allotrope.
abstract: The optical and electronic properties of semiconducting materials are of great importance to a vast range of contemporary technologies. Diamond-cubic germanium is a well-known semiconductor, although other 'exotic' forms may possess distinct properties. In particular, there is currently no consensus for the band gap and electronic structure of ST12-Ge (tP12, P43212) due to experimental limitations in sample preparation and varying theoretical predictions. Here we report clear experimental and theoretical evidence for the intrinsic properties of ST12-Ge, including the first optical measurements on bulk samples. Phase-pure bulk samples of ST12-Ge were synthesized, and the structure and purity were verified using powder X-ray diffraction, transmission electron microscopy, Raman and wavelength/energy dispersive X-ray spectroscopy. Optical measurements indicate that ST12-Ge is a semiconductor with an indirect band gap of 0.59 eV and a direct optical transition at 0.74 eV, which is in good agreement with electrical transport measurements and our first-principles calculations.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.|State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
authors.forename: Zhisheng
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.
authors.forename: Haidong
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.|Center for High Pressure Science and Technology Advanced Research, 1690 Cailun Road, Building 6, Pudong, Shanghai 201203, China.
authors.forename: Duck Young
authors.initials: DY
authors.lastname: Kim
authors.affiliation: State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
authors.forename: Wentao
authors.initials: W
authors.lastname: Hu
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.
authors.forename: Emma S
authors.initials: ES
authors.lastname: Bullock
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia 20015, USA.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Strobel