Temperature-dependent growth of few layer β-InSe and α-In₂Se₃ single crystals for optoelectronic device

Controllably selective growth of two-dimensional (2D) layered single crystals plays an important role for their applications in electronic and optoelectronic devices. Among these 2D materials, indium selenide (In_xSe_y), especially InSe and In₂Se₃, are typical III-VI compound semiconductors which have attracted particular attention due to their excellent electronic transport properties, photoresponse and nonlinear effect. However, controllably selective growth of 2D InSe and In₂Se₃ by a common method is still a great challenge due to the existence of various stoichiometric substances and crystalline phases of each substance in the indium selenide system. Here, we demonstrate a temperature-dependent chemical vapor transport (CVT) strategy to synthesize few-layer β-InSe and α-In₂Se₃ single crystals at 400 °C and 450 °C on mica substrate, respectively. A few-layer β-InSe photodetector was fabricated, which displayed high sensitivity to a broad photoresponse range from visible light (500 nm) to near infrared light (850 nm) with a high responsivity of 2103 A W^-1 and detectivity of 4.25 ×10¹² Jones illuminated by 500 nm. Moreover, we first demonstrate the piezo-phototronic effect of 2D α-In₂Se₃. The photodetection performance of α-In₂Se₃ photodetector was increased by 35% with a uniaxial tensile strain of 0.44% under 700 nm light. Our work demonstrates that few-layer β-InSe and α-In₂Se₃ single crystals can not only be synthesized selectively, but also exhibit excellent optoelectronic properties, which paves a way for their application in optoelectronic and flexible devices.