Investigation of dual-wavelength selective self-powered photo response of ZnO/Si heterojunction with insertion of thin TiO2 layer

In the current work, ZnO film (similar to 143 nm) is deposited on the CMOS compatible Si substrate by using RF sputtering technique to form a p-n type heterojunction device and further, thin buffer layer of TiO2 (similar to 52 nm) is inserted in between ZnO and Si to reduce the interfacial defects remarkably in ZnO/TiO2/Si bilayer heterojunction for UV/Visible sensing applications. Smooth interface, and highly crystallite qualities of TiO2-brookite and ZnO-hexagonal wurtzite phases are observed from atomic force microscopy (AFM) and Field-emission gun scanning electron microscopy (FEG-SEM) and X-ray diffraction (XRD), respectively. X-ray photoelectron spectroscopy (XPS) clarifies the chemical states of elements, which indicate a significant amount of the reduction in oxygen vacancies after insertion of the TiO2 thin layer. An enhanced absorption in UV region and slight red shift in emission are observed in UV-Visible spectroscopy and Photoluminescence (PL) plots for TiO2/ZnO bilayer heterojunction, and oxygen related complex defects are reduced due to TiO2 insertion. Finally, Current-voltage (I-V) measurements demonstrate the dark current reduction in ZnO/Si heterojunction with TiO2 incorporation and such heterojunction exhibits photovoltaic behavior under specific wavelengths (380 nm and 420 nm). A superior responsivity (0.17 A/W), detectivity (7.80 x 10(13) Jones) with rapid response speed (< 1 s) at zero bias are achieved in the UV-A/Visible wavelength range for ZnO/TiO2/Si heterojunctions. The corresponding photo-carrier generation and transport mechanism are analyzed in detail by using corresponding energy band diagram. Therefore, all the results indicate that such TiO2 thin layer inserted ZnO/Si heterojunction may provide a cost-effective feasible design strategy for the development of interfacial defect less, self-powered wavelength selective UV/Visible detectors in recent future.