Significant anisotropy in photoelectronic response of SnSe nanosheets

SnSe, a type of class IV-metal monochalcogenide, exhibits good electrical and optoelectronic properties in the near-infrared band. Due to the low symmetry of the lattice structure, two-dimensional SnSe is expected to show significant anisotropic electric and optoelectric properties. However, this anisotropy has not been fully studied until now because of the difficulty of obtaining high quality single-crystalline SnSe nanosheets. In this manuscript, single-crystalline SnSe nanosheets with thicknesses varying from 7 to 100 nm and a lateral size of 10 μm were deposited via a low-pressure chemical vapor deposition method. The high quality of pure α-SnSe single-crystalline nanosheets was confirmed by x-ray diffraction and high-resolution transmission electron microscopy. Furthermore, the anisotropic electric transport properties of SnSe were investigated. Higher conductance along the zigzag direction was observed under all gate biases. The anisotropic ratio of conductance is as high as 2.1 under zero gate bias. Finally, the anisotropic photoelectric properties were characterized with the 532 and 808 nm lasers, respectively. A higher photocurrent and responsivity were obtained along the zigzag direction, which may be a result of higher conductance along the specific direction. More importantly, the photoresponsivity of 132 A/W with a specific detectivity of 2.75 × 108 was achieved with an 808 nm laser, which rivals the performance of current commercial infrared photodetectors used at room temperature.