An experimental and theoretical understanding of a UV photodetector based on Ag nanoparticles decorated Er-doped TiO2 thin film

Abstract

Glancing angle deposition (GLAD) was employed to synthesise plasmonic Silver (Ag) nanoparticles (NPs) on the chemically prepared Erbium-doped Titanium dioxide (Er:TiO2) thin films (TFs). The impact of using Ag NPs on the morphological, optical, and electrical aspects of Er:TiO2 TFs were sequentially analysed. From the field emission scanning electron microscopy (FESEM) image, the Ag NPs appeared spherical and uniformly distributed on the Er:TiO2 TFs. The size (diameter) of the maximum number of Ag NPs was ~15 nm (calculated from FESEM image). Energy dispersive X-ray (EDX) spectra assured the presence of Ag NPs on the TFs. X-ray diffraction (XRD) pattern for Ag NPs decorated Er:TiO2 TFs closely resembled the face centred cubic crystal structure of Ag NPs and body centred tetragonal Ag–O compound. The optical spectroscopy (UV–visible diffuse reflectance and photoluminescence) elucidated that the absorption of light was significantly enhanced in the UV–visible spectral range for the TFs in which Ag NPs were sandwiched between Er:TiO2 TF layers (Er:TiO2/Ag NPs/Er:TiO2). The Schottky contact-based Au/Er:TiO2/Si photodetector (PD) and Au/Er:TiO2/Ag NPs/Er:TiO2/Si (plasmonic) PD were constructed. The plasmonic PD offered a better photo-responsivity of ~4.5 fold higher as compared to Er:TiO2 TF-based PD upon 380 nm illumination under −6 V bias. An increase in detectivity and a decrease in noise equivalent power was observed for the plasmonic device compared to Er:TiO2 device in the UV region. A theoretical approach had been adopted to calculate the wavelength-dependent responsivity for both devices. Further, the important parameters like photoconductive gain, electron transit time and electron mobility were calculated by simulating the experimental responsivity curves of the devices. These parameters exhibited improvement in the UV regime for the plasmonic PD. The fast temporal response with short rise and decay time proves the excellent efficiency of the plasmonic UV PD.