# High-Pressure Synthesis and Characterization of $\beta$-GeSe - A Semiconductor with Six-Rings in an Uncommon Boat Conformation

## TL;DR

This paper reports the discovery and characterization of a new polymorph of GeSe, called $eta$-GeSe, with a unique boat conformation of six-rings, exhibiting semiconducting properties suitable for future electronic applications.

## Contribution

The study introduces $eta$-GeSe as a novel high-pressure synthesized polymorph with distinct structural and electronic properties compared to known GeSe forms.

## Key findings

- $eta$-GeSe has a bulk band gap of approximately 0.5 eV.
- Monolayer $eta$-GeSe has a band gap of approximately 0.9 eV.
- Resistivity of $eta$-GeSe crystals is about 1 Ω·cm and temperature-independent.

## 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.