RESUMEN
Two-dimensional (2D) GeSe has been proven promising in fast and broadband optoelectronic applications for its complicated band structure, inert surface property, and excellent stability. The major challenge is the deficiency of the effective technique for controllably prepared large-scale few-to-monolayer GeSe films. For this purpose, a layer-by-layer thinning method by thermal sublimation for manufacturing large-scale mixed few-layer GeSe with direct bandgaps is proposed, and an optimized sublimation temperature of 300 °C in vacuum is evaluated by atomic force microscopy. Scanning electron microscopy, transmission electron microscopy, energy-dispersive spectra, and fluorescence mapping measurements are performed on the thinned GeSe layers, and results are well-indexed to the orthorhombic lattice structure with direct bandgaps with an atomic ratio of Ge/Se ≈ 5:4. Raman and fluorescence spectra show an α-type crystalline structure of the thinned GeSe films, indicating the pure physical process of the sublimation thinning. Both the bulk and few-layer GeSe films demonstrate broadband absorption. Conductivity of the few-layer GeSe device indicates the overall crystalline integrity of the film after thermal thinning. Given the convenience and efficiency, we provide an effective approach for fabrication of large-scale 2D materials that are difficult to be prepared by traditional methods.
RESUMEN
Owing to the attractive energy band properties, a black phosphorus (BP)-analogue semiconductor, germanium selenide (GeSe), shows a promising potential applied for optoelectronic devices. Herein, ultrathin GeSe nanosheets were systematically prepared via a facile liquid-phase exfoliation approach, with controllable nanoscale thickness. Different from BP, ultrathin GeSe nanosheets exhibit good stability under both liquid and ambient conditions. Besides, its ultrafast carrier dynamics was probed by transient absorption spectroscopy. We showed that the GeSe nanosheet-based photodetector exhibits excellent photoresponse behaviors ranging from ultraviolet (UV) to the visible regime, with high responsivity and low dark current. Furthermore, the detective ability of such a device can be effectively modulated by varying the applied bias potential, light intensity, and concentration of the electrolyte. Generally, our present contribution could not only supply fundamental knowledge of a GeSe nanosheet-based photoelectrochemical (PEC)-type device, but also offer guidance to extend other possible semiconductor materials in the application of the PEC-type photodetector.