Long-Hui Zeng, Di Wu, Sheng-Huang Lin, Chao Xie, Hui-Yu Yuan, Wei Lu, Shu Ping Lau, Yang Chai, Lin-Bao Luo,* Zhong-Jun Li, * and Yuen Hong Tsang*

Abstract:Palladium diselenide (PdSe₂), a thus far scarcely studied group-10 transition metal dichalcogenide (TMD) has exhibited promising potential in future optoelectronic and electronic devices due to unique structures and electrical properties. Here, we reported on the controllable synthesis of wafer-scale and homogenous two-dimensional (2D) PdSe₂ film by a simple selenization approach. By choosing different thickness of precursor Pd layer, 2D PdSe2 with thickness of 1.2 to 20 nm can be readily synthesized. Interestingly, with the increase in thickness, obvious red shift in wavenumber is revealed by Raman spectroscopy. Moreover, in accordance with density functional theory (DFT) calculation, optical absorption and ultraviolet photoemission spectroscopy (UPS) analysis confirm that the PdSe₂ exhibits an evolution from a semiconductor (monolayer) to semimetal (bulk). Further combination of the PdSe₂ layer with Si leads to a highly sensitive, fast and broadband photodetector with a high responsivity (300.2 mA/W) and specific detectivity (~10¹³ Jones). By decorating the device with black phosphorus quantum dots (BPQDs), the device performance can be further optimized. These results suggest the as-selenized PdSe₂ is a promising material for optoelectronic application.