Colloidal ZnO Quantum Dots Based Spectrum Selective Ultraviolet Photodetectors

This letter reports (possibly for first time) the synthesis, fabrication, and characterization of a solution processed colloidal ZnO quantum dots (QDs) photoconductor-based spectrum selective ultraviolet (UV) photodetector on low-cost glass substrates without using any additional absorption tuning layer. The QD nature of colloidal ZnO was confirmed by transmission electron microscopy measurements in terms of average particle size (~2.53nm) smaller than Bohr's radius (~2.87 nm for ZnO). Furthermore, annealing at the ambient environment showed a shift in the bandgap from 3.231 to 3.136 eV of the ZnO QDs corresponding to the change in the annealing temperature from 450 °C and 600 °C. The responsivity characteristics showed a spectrum selective UV photoconductor nature with a full width half maximum of ~49 nm and the maximum responsivity of ~15.04 A/W at 2 V bias voltage and ~360-nm operating wavelength. The response time and recovery time were measured as 7.2 and ~18.5 s, respectively. The responsivity is believed to be the best among the reported ZnO QDs-based spectrum selective detectors.