Large-Area Synthesis of Layered HfS Se Alloys with Fully Tunable Chemical Compositions and Bandgaps.

Alloying transition metal dichalcogenides (TMDs) with different compositions is demonstrated as an effective way to acquire 2D semiconductors with widely tunable bandgaps. Herein, for the first time, the large-area synthesis of layered HfS Se alloys with fully tunable chemical compositions on sapphire by chemical vapor deposition is reported, greatly expanding and enriching the family of 2D TMDs semiconductors. The configuration and high quality of their crystal structure are confirmed by various characterization techniques, and the bandgap of these alloys can be continually modulated from 2.64 to 1.94 eV with composition variations. Furthermore, prototype HfS Se photodetectors with different Se compositions are fabricated, and the HfSe photodetector manifests the best performance among all the tested HfS Se devices. Remarkably, by introducing a hexagonal boron nitride layer, the performance of the HfSe photodetector is greatly improved, exhibiting a high on/off ratio exceeding 10, an ultrafast response time of about 190 µs, and a high detectivity of 10 Jones. This simple and controllable approach opens up a new way to produce high-quality 2D HfS Se layers, which are highly qualified candidates for the next-generation application in high-performance optoelectronics.