Enhancing the properties of CdO thin films by co-doping with Mn and Fe for photodetector applications

Abstract

In this communication, we report on how the co-doping of two transition metal ions (Fe and Mn) effectively improves the structural, morphological, optical, electrical and photodetection properties of CdO thin films than individual doping. For this, pure-CdO, Fe-doped, Mn-doped and (Fe-Mn) co-doped CdO thin films are deposited by spray pyrolysis technique. X-ray diffraction (XRD) patterns reveal that these films possess cubic structure and belong to the Fm-3 m space group. The Field Emission Scanning Electron micrographs hold a qualitative agreement with the crystalline sizes obtained from the XRD analysis. Energy Dispersive X-Ray Analysis approved the existence of constituent elements in the prepared films. The photoluminescence spectra identified the quality of crystal structure and the presence of defects in the prepared films. Analyzing the absorption spectra unveiled the direct bandgap values in the range 2.32 eV (for pure-CdO) - 1.96 eV (for CdO:Fe(1%):Mn(1%)). The Hall Effect measurements established n-type behavior with the values of resistivity (ρ), carrier concentration (n) and carrier mobility values in the range 5.8–7.1 mΩcm, 6.7−2.4 × 1019 cm−3 and 16−37 cm2/Vs, respectively. Three different transport mechanisms such as ohmic, recombination-tunneling and space-charge limited current are found to play roles in the three distinct ranges of the I–V data measured for the films under study. The ideality factor values are obtained from the region where the recombination-tunneling mechanism is prevalent. The photoelectric parameters such as photo-responsivity, and external quantum efficiency are obtained. The values of these quantities pertaining to pure-CdO, CdO:Mn, CdO:Fe and CdO:Fe:Mn films vary in the range 128.4–561.3 mA/W, and 30–131.1 %, respectively. From the current study, it was found that photoresponsivity and external quantum efficiency are enhanced by a factor of four in codoped CdO films than the undoped CdO film and can find potential photodetector applications.