α-In2Se3 Nanostructure-Based Photodetectors for Tunable and Broadband Response

The strong thickness-dependent narrow direct band gap of few-layer α-In2Se3 makes it a promising candidate for high-performance photodetectors. However, few researchers focus on the relationship between thickness and optoelectronic characteristics, and most results are based on the mechanically exfoliated α-In2Se3 nanoflakes. Herein, a reliable physical vapor deposition strategy to grow α-In2Se3 nanosheets with tunable thickness and submillimeter scale is reported. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) studies confirmed the high-quality growth of α-In2Se3 nanosheets. The back-gate field-effect transistors on SiO2 substrates display n-type semiconductor behavior. A systematical investigation of the optoelectronic properties reveals a thickness-dependent broadband response from visible (447 nm) to near-infrared (1550 nm) wavelengths with better and excellent performance obtained in thicker α-In2Se3 nanosheets than that in thinner devices. More importantly, a great improvement of the responsivity, detectivity, and external quantum efficiency (EQE) can be achieved by changing the thickness of In2Se3. The photodetector exhibits an outstanding photoresponsivity of 347.6 A/W, an ultrahigh detectivity of 1.5 × 1013 Jones, and an external quantum efficiency of 8.3 × 104%, which is superior to several α-In2Se3 nanostructure- or other two-dimensional (2D)-based photodetectors. The thickness-dependent broadband response characteristics make the α-In2Se3 nanostructure a promising candidate for multifunctional optoelectronic device applications.