2026
This paper is fruit of my Undergraduate Senior Thesis at Physics Intistute of University of
Brasília and also from an undergraduate research project (PIBIC in Brazil) developed at the same place.
In this work, ZnO thin films were deposited by DC magnetron sputtering under varying working pressures and subsequently annealed in air, followed by vacuum thermal annealing. The increase of working pressure drive to the reduction of the film thickness, crystallite size, lattice constants, and to the strengthening of the (002) X-ray diffraction peak, suggesting changes in the in oxygen vacancy concentration. Scanning electron microscopy revealed the formation of randomly distributed nanorods, while UV–Vis spectroscopy data analysis evidenced the presence of defect-related levels inside the band gap. As the thickness decreases, Hall measurements show a noticeable drop in charge carrier density and mobility, which is linked to the combined impact of defects and the decreasing size of crystallites. This suggests that thicker films exhibited a higher density of zinc interstitials, whereas thinner films exhibit more oxygen vacancies (Vo), mainly associated with surface states, as supported by temperature-dependent resistance measurements and photocurrent analysis. Gas detection tests demonstrated a superior response to methane (CH4) for thinner films at 200 °C, attributed to their higher oxygen vacancy concentration. Photocurrent and gas sensing measurements showed similar trends, indicating a common defect-driven mechanism. These results highlight the potential of tuning defect chemistry in ZnO films to optimize their performance for gas sensing and optoelectronic devices.