Large‐Area Synthesis of Layered HfS₂₍₁₋<i>_x</i>₎Se₂<i>_x</i> Alloys with Fully Tunable Chemical Compositions and Bandgaps

Abstract

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_2(1- _x ₎Se₂ _x 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_2(1- _x ₎Se₂ _x photodetectors with different Se compositions are fabricated, and the HfSe₂ photodetector manifests the best performance among all the tested HfS_2(1- _x ₎Se₂ _x devices. Remarkably, by introducing a hexagonal boron nitride layer, the performance of the HfSe₂ photodetector is greatly improved, exhibiting a high on/off ratio exceeding 10⁵, an ultrafast response time of about 190 µs, and a high detectivity of 10¹² Jones. This simple and controllable approach opens up a new way to produce high-quality 2D HfS_2(1- _x ₎Se₂ _x layers, which are highly qualified candidates for the next-generation application in high-performance optoelectronics.