Synthesis and characterization of single-crystal CdS nanosheet for high-speed photodetection

Abstract

One-dimensional nanostructures have several unique advantages over bulk material and thin films, which can be exploited for high-speed photodetection. Furthermore, as bulk CdS has a high photosensitivity and quantum efficiency, there is considerable potential for the use of CdS nanostructures in advanced devices. In this study, single-crystal CdS nanosheets were grown by thermal evaporation and fully characterized to determine their potential for application in high-speed photodetectors. A high-quality nanosheet was confirmed to have a smooth surface with no extraneous particles and a strong orientation to the (110) plane of the wurtzite (hexagonal) phase of CdS. The Cd/S ratio was found to be nearly stoichiometric at 1.09. Photoluminescence measurement of a single-crystal CdS nanosheet showed a high emission intensity at a wavelength of 493nm. The current–voltage characteristics of the CdS nanosheet on Al thin film indicated an Ohmic contact in dark and under illumination by ambient, 365-nm, 405-nm, and 460-nm light. The light responsivity showed a peak at 460nm. Under 365-nm, 405-nm, and 460-nm chopped light, at a bias voltage of 1, 3, and 5V, the photocurrent rise and decay times were investigated. The device showed faster response times for 460-nm light. This fast response was attributed to the high quality of the single crystal, the absence of defect states, and the high surface/volume ratio. The device showed a high quantum efficiency of 22.3×103% when it was illuminated by 365-nm light under a bias of 5V; this efficiency increased to 36.3×103% and 40.5×103% when the device was illuminated by 405-nm and 460-nm light, respectively.