Germanium Diselenide Ribbons with Orthorhombic Crystal Structure.

Many materials are known to exist in several stable polymorphs, but synthesis only provides access to a subset. This situation is exemplified by the dichalcogenide semiconductor GeSe. Besides the amorphous form, which attracted intense interest, crystalline GeSe in the bulk and in nanostructures such as flakes and nanobelts invariably adopts the 2D/layered monoclinic β-phase. Hence, the properties of other polymorphs such as the orthorhombic 3D GeSe phase remain unknown. Here, we report the high-yield synthesis of orthorhombic GeSe nanoribbons by GeSe/Se vapor transport over Au catalysts. Access to air-stable monocrystalline, single-phase ribbons enabled investigating the properties of orthorhombic GeSe including its characteristic Raman spectrum. Optical absorption on ensembles and cathodoluminescence spectroscopy on individual ribbons show a wide bandgap and intense band-to-band emission in the visible, with a broad sub-bandgap emission tail. Our results establish orthorhombic GeSe ribbons as a promising wide-bandgap semiconductor nanostructure for applications in optoelectronics and energy conversion.