Highly anisotropic solar-blind UV photodetector based on large-size two-dimensional α-MoO₃ atomic crystals

Orthorhombic MoO₃ (α-MoO₃) is a typical layered n-type semiconductor with optical band gap over 2.7 eV, which have been widely studied in catalysis, gas sensing, lithium-ion batteries, field-emission, photoelectrical, photochromic and electrochromic devices, supercapacitors and organic solar cells. However, the bottleneck of generation large size atomic thin two-dimensional (2D) α-MoO₃ crystals remain challenging this field (normally several micrometers size). Herein, we developed a facile vapor-solid (VS) process for controllable growth of large-size 2D α-MoO₃ single crystals with a few nanometers thick and over 300 μm in lateral size. High-performance solar-blind photodetectors were fabricated based on individual 2D α-MoO₃ single crystal. The detectors demonstrate outstanding optoelectronic properties under solar-blind UV light (254 nm), with a photoresponsivity of 67.9 A W^-1, external quantum efficiency of 3.3 × 10⁴%. More important, the devices showed strong in-plane anisotropy in optoelectronic response and transport properties, e.g. the photocurrent along b-axis was found to be 5 times higher than the values along c-axis under 254 nm UV light, and current ON/OFF ratio and mobility anisotropy is about 2 times high. Our work suggests an optimized synthesis routine for 2D crystals, and the great potential of 2D oxides in functional optoelectronics.