Multi-band visible photoresponse study of Co2+ doped ZnO nanoparticles

In this article, near UV (NUV) and near UV-visible photodetectors (PDs) were fabricated using pure (ZnO) and Co doped ZnO (Zn1-xCoxO) nanoparticles synthesised by co-precipitation method. The structural, morphological, compositional and chemical state analysis of the nanoparticles were done using X-ray diffractometry, transmission electron microscopy, energy dispersive spectrometry and X-ray photoelectron spectrometry respectively. The optical spectra which were recorded using a UV-Vis spectrometer exhibited the presence of absorption peaks in the visible region for Co doped ZnO due to d-d transitions. Enhanced photoresponse in the NUV region was found in lower doping concentrations and all the Co doped ZnO photodetectors showed a noticeable response to visible light sources. A maximum responsivity of 63 mA W-1 and quantum efficiency of similar to 20% was achieved in the NUV region for the PD fabricated with 2 at% Co doping. The 2 at% Co doped ZnO based photodetector showed efficiency in the range 11-35% for the wavelengths from 401 to 634 nm.