Effects of Optical Resonance on the Performance of Metal (Pd, Au)/CdSe Quantum Dots (QDs)/ZnO QDs Optical Cavity Based Spectrum Selective Photodiodes

In this paper, we have reported the effect of optical resonance on the spectrum selectivity, external quantum efficiency (EQE), and time response of Metal (Pd, Au)/CdSe quantum dots (QDs)/ZnO QDs optical cavity based Schottky photodiodes on the ITO coated glass substrates. The CdSe QDs layer acts as the active layer while the ZnO QDs layer act as the electron transport layer (ETL) as well as a filter layer. The optical illumination is coupled into the device through the substrate side to enhance the optical absorption in the active layer due to multiple reflections from both metal (Pd, Au)/ CdSe QDs and CdSe QDs/ZnO QDs interfaces. The measured photoresponse over the 350-650 nm gives ~61 nm (190 nm), 2.21% (0.87%), and 17.15 ms (28.9 ms) values for the full width at half maximum (FWHM), EQE, and response time of Pd (Au)/CdSe QDs based Schottky photodiodes, respectively. The improvements in the spectrum selectivity, EQE, and response time due to the change in the Schottky electrode from Au to Pd are attributed to higher reflection characteristic of the Pd/CdSe QDs interface than that of the Au/CdSe QDs interface which are duly justified by measured results and theoretical models presented in this paper. An improved responsivity with reduced FWHM obtained by merely replacing the Au by Pd is possibly reported for the first time for the spectrum selective photodetectors.