Low temperature UV assisted water based solution processing: investigation of structural, optical, and electrical characteristics of yttrium oxide thin films

Abstract This work presents the UV annealing method (UVAM) as an efficient way to produce yttrium oxide (Y 2 O 3 ) thin films, using water-based solution processing. The effect of increasing UV exposure (30-, 60-, 90-, and 120 min) on the microstructure, optical and electrical properties of Y 2 O 3 films has been investigated and also compared with a thermally (at 350 °C) annealed film. All the films are found to be amorphous (via x-ray diffraction, Raman spectroscopy) with a decreasing crystallinity component (representing increasing disorder) have a smooth-to-grainy surface morphology (via scanning electron microscopy) and exhibit oxygen deficiency with increasing UVAM exposure. The fourier transform infrared spectroscopy (FTIR) analysis reveals characteristic footprints of Y–O vibrations with minimal traces of impurities. An increasing trend in optical transmittance (80%–89%), while a decrease in band gap energy ( E g ) (4.58–4.10 eV) is observed from UV–Vis spectroscopy. Spectroscopic ellipsometry measurements have confirmed that defects play a substantial role in the dispersion profiles of the optical constants of Y 2 O 3 films. Considerable increases in the refractive index ( n ) (1.62–2.25) and dielectric constant ( ϵ r ) (2.62–5.28) are observed in UVAM Y 2 O 3 films compared to thermally treated films. The luminescence bands in photoluminescence (PL) spectra are ascribed to the transitions from donor acceptor pairs and oxygen related defects. Furthermore, the increase in both the PL peak intensity and the carrier concentration with the decrease in the electrical resistivity (6–1.8 × 10 4 Ω cm), found from Hall Effect measurements, confirms the effective photo functionalization induced by UVAM in Y 2 O 3 films. We have also obtained a significant improvement of optoelectronic figure of merit ( ϕ = 1.01 × 10 −5 (Ω cm) −1 ) with UVAM. A clear connection between the UVAM and optical and/or electrical parameters found for Y 2 O 3 films confirms that tuning these characteristics for tailor-made applications is achievable through UVAM, which has established its potential to produce Y 2 O 3 thin films with performance on par with high temperature annealing-based films. Also, water-based solution processing offers a straightforward and low-cost method as an alternate for flexible and environmentally friendlier opto-electronic technologies.