Role of surface induced defects in modulating persistent photoconductivity of spray pyrolyzed Zn0.93Sm0.07O thin films

The influence of surface induced defect states on the structural, optical, electrical properties and optoelectonic properties of Zn 0.93 Sm 0.07 O thin films were systematically examined to assess their potential for optoelectronic applications, specifically as ultraviolet (UV) photodetectors by varying the substtrate temperature (300 °C – 500 °C in the interval of 50 °C). X-ray diffraction analysis confirmed the wurtzite crystal structure for all the films, with optimal crystalline quality achieved at a substrate temperature of 450 °C, evidenced by an intense (0 0 2) peak. Scanning electron microscopy showed fibrous morphology for all the deposited films and energy-dispersive X-ray analysis validated the effective incorporation of Sm 3+ ions and reduced defect density at higher temperatures. The optical characterization revealed enhanced transparency and a reduced bandgap for films deposited at 450 °C. The photoluminescence spectra showed stronger near-band-edge emission and diminished defect-related emissions. Electrical measurements demonstrated better performance at 450 °C including higher photocurrent, faster rise and fall times. The efficient photoresponse was centered at 370 nm, attributed to improved charge carrier mobility and lower defect concentration due to lesser surface defects present in the deposited films. In contrast, films deposited at 300 °C exhibited reduced photocurrent due to increased defect trapping. These findings highlight the importance of substrate temperature in tuning material properties, with Zn 0.93 Sm 0.07 O films deposited at 450 °C emerging as promising candidates for high-performance UV photodetectors.