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 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-membered ring ("six-ring"), while the previously known a 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 approximate to 0.5 eV, and, in its monolayer form, Delta approximate to 0.9 eV. These values fall between those of a-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 approximate to 1 Omega.cm, while being essentially temperature independent.