Comparative study of ZnO and WO3 thin films grown by pulsed laser deposition at similar substrate temperatures

Abstract

In this work, zinc oxide (ZnO) and tungsten trioxide (WO3) thin films were grown by a pulsed laser deposition (PLD) technique at an elevated substrate temperature of 400ºC. The PLD technique involves using a high-intensity laser to vaporize and deposit material onto an n-type silicon (Si) substrate. The field emission gun scanning electron microscopy (FEG-SEM) was employed to visualize and characterize the morphology of the two samples viz., ADW4 and ADZn4. The grazing incidence X-ray diffraction (GIXRD) was used to assess the crystallite structure of the two thin films based samples. The study found that ADW4 exhibited a significantly smaller average crystallite size (6.48 nm) compared to ADZn4 (16.22 nm). The smaller crystallite size of ADW4 is noteworthy and indicates the potential presence of quantum confinement effects, which are crucial in the development of optoelectronic devices such as light-emitting diodes (LEDs), and photodetectors. The room-temperature photoluminescence (RTPL) emission peak for ADW4 and ADZn4 was found to be at 323 nm (3.84 eV) and 379 nm (3.27 eV), respectively, under an excitation wavelength of 300 nm. The RTPL spectra revealed that the peak at around 323 nm for ADW4 gradually shifted towards the ultra-violet (UV) region compared to ADZn4 (379 nm). Significantly, such blue emission is shifted towards the UV-A region in ADW4 suggesting that it could be used to produce UV-A LEDs, which have applications in disinfection, water purification, and UV curing processes.