High quality, highly transparent Cu incorporated WO3 thin films suitable for blue LED application

Abstract

Good crystalline Cu doped WO3 thin films are prepared using Radio Frequency (RF) magnetron sputtering and the films are characterised using various characterisation tools. Structural study using X-ray diffraction technique (XRD) and Micro-Raman Spectroscopy confirms the formation of monoclinic WO3 phase in all the films. The prepared films are preferentially oriented along a-axis and the film with 3 wt% Cu concentration show better crystalline quality. Morphological analysis (Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM)) and elemental analysis (Energy Dispersive X-ray Spectroscopy (EDX)) show that Cu nanoparticles can act as seeding sites for the formation of bigger clusters in the films. The valence states of Cu in the prepared thin films are found to be +2 and 0 and/or +1 using X-ray Photoelectron Spectroscopic (XPS) study. The dip in the transmittance spectra and the corresponding enhanced absorption in the absorbance spectra around 620 nm region of 5 and 7 wt% Cu doped films detected using UV–Visible analysis can be attributed to localised surface plasmon resonance (LSPR) behaviour of Cu nanoparticles in these films. LSPR behaviour of Cu nanoparticles at higher Cu doped films suggests their suitability for improving the quantum efficiency of various photonic devices. A band gap renormalisation from 3.14 eV to 2.97 eV can be observed with increase in Cu incorporation concentration. Emission behaviour of Cu doped WO3 films are studied for their visible colour perception which show chromaticity coordinates corresponding to intense blue colour. The intense blue emission from Cu doped WO3 thin films suggests their suitability in blue light emitting diodes and in phosphor converted white light emitting diodes.