Cryogenic UV detection using stress-engineered zero-bias ZnO-thin film based Piezo-Photonic detector

Abstract: We demonstrate a zero-bias ultraviolet (UV) detector using zinc oxide (ZnO) thin films as the active semiconductor layer, specifically for application in cryogenic conditions. The zero-bias device utilizes the piezoelectric potential developed through interfacial stress in the active semiconductor layer for charge transport. We explored two vertically stacked metal-semiconductor-metal (MSM) configurations: Sample I, a device comprised of chromium (Cr)/ZnO/Cr layers, and Sample II, a ZnO-silicon nitride (Si3N4) device comprised of Cr/Si3N4/ZnO/Cr layers. The Si3N4 layer in Sample II was introduced in the form of pillars, with the aim of increasing the residual stress in the active region. These fabricated devices were tested at both room and cryogenic temperatures to characterize their UV-detection performance in a custom test stand using a 365 nm UV LED source. We observe a higher UV-induced voltage signal for Sample II in comparison to Sample I at both temperature regimes. Grazing-incidence X-ray diffraction (GIXRD) measurements showed approximately 40% higher residual stress in Sample II than in Sample I. A higher residual stress suggests a higher induced piezopotential in Sample II, explaining the enhancement in the UV-induced signal. Our results demonstrate that through appropriate in-device stress engineering, UV photoinduced signals can be enhanced, increasing detector sensitivity. A zero-bias photodetector with in-device stress engineering, as demonstrated here, can have applications in extreme environments, like cryogenic liquid noble elements or high radiation space environments, where low or zero-power detection may be required.