High-Pressure Synthesis and Characterization of β‑GeSeA Six-Membered-Ring Semiconductor in an Uncommon Boat Conformation

Two-dimensional materials have significant
potential for the development
of new devices. Here we report the electronic and structural properties
of β-GeSe, a previously unreported polymorph of GeSe, with a
unique crystal structure that displays strong two-dimensional structural
features. β-GeSe is made at high
pressure and temperature and is stable under ambient conditions. We
compare it to its structural and electronic relatives α-GeSe
and black phosphorus. The β form of GeSe displays a boat conformation
for its Ge–Se six-membered ring (“six-ring”),
while the previously known α form and black phosphorus display
the more common chair conformation for their six-rings. Electronic
structure calculations indicate that β-GeSe is a semiconductor,
with an approximate bulk band gap of Δ ≈ 0.5 eV, and,
in its monolayer form, Δ ≈ 0.9 eV. These values fall
between those of α-GeSe and black
phosphorus, making β-GeSe a promising candidate for future applications.
The resistivity of our β-GeSe crystals measured in-plane is
on the order of ρ ≈ 1 Ω·cm, while being essentially
temperature independent.