Stoichiometry-controlled synthesis and optoelectronic performance of 2D InSe

Two-dimensional (2D) indium selenide (InSe) is a promising semiconductor for next-generation optoelectronics, but high quality nanoflakes with controllable stoichiometric ratios have not yet been achieved. Furthermore, their performance suffers from defect-related limitations. We report a crystal growth strategy that adopts various stoichiometric ratios of In/Se in the melt. Two types of high crystallinity InSe and InSe_0.92 crystals were acquired by the vertical Bridgman (VB) method, enabling precise regulation of defects. The distinct chemical compositions and crystal structures of the derived indium selenide with different stoichiometric ratio will be revealed with the aid of multiscale characterization techniques. The as-obtained crystals demonstrate exceptional composition uniformity, a pure phase structure, and high crystallinity. The two types of crystals, InSe and InSe_0.92, exhibit different defect concentrations and types. In addition, their optoelectrical devices are also examined to unravel the stoichiometry-dependent electronic properties. Optoelectronic devices based on the produced InSe_0.92 nanoflakes demonstrate outstanding electronic transport performance surpassing that of InSe-based devices, including an extremely high photoresponsivity (from 0.132 to 169.731 A W⁻¹) at room temperature. However, optoelectronic devices based on InSe nanoflakes demonstrate fast response speed (a rise time of 6.157 to 0.078 s and a decay time of 0.167 to 0.04 s). Overall, this research is expected to propel the stoichiometry-tunable fabrication, the related physical property explorations, and the versatile applications of 2D indium selenide materials in next-generation electronic and optoelectronic devices.