Title: High-Pressure Synthesis and Characterization of $β$-GeSe - A Semiconductor with Six-Rings in an Uncommon Boat Conformation,
Abstract: Two-dimensional materials have significant potential for the development of
new devices. Here we report the electronic and structural properties of
$\beta$-GeSe, a previously unreported polymorph of GeSe, with a unique crystal
structure that displays strong two-dimensional structural features.
$\beta$-GeSe is made at high pressure and temperature and is stable under
ambient conditions. We compare it to its structural and electronic relatives
$\alpha$-GeSe and black phosphorus. The $\beta$ form of GeSe displays a boat
conformation for its Ge-Se six-ring, while the previously known $\alpha$ form,
and black phosphorus, display the more common chair conformation for their
six-rings. Electronic structure calculations indicate that $\beta$-GeSe is a
semiconductor, with an approximate bulk band gap of $\Delta~\approx$ 0.5 eV,
and, in its monolayer form, $\Delta~\approx$ 0.9 eV. These values fall between
those of $\alpha$-GeSe and black phosphorus, making $\beta$-GeSe a promising
candidate for future applications. The resistivity of our $\beta$-GeSe crystals
measured in-plane is on the order of $\rho \approx$ 1 $\Omega$cm, while being
essentially temperature independent.