Metal oxide nanostructure based ultraviolet photodetectors for smart lighting applications

Abstract

A modular polystyrene spheres-based template assisted solvothermal method is also present-ed for the synthesis of zinc oxide and beta gallium oxide hollow nanospheres. Template-based method allows higher tunability of the hollow sphere morphology. These materials are suitable for fabrication of UV-A and UV-C photodetectors.

Ultraviolet (UV) photodetectors are used in a wide range of applications including safety ap-plications such as electric arc and flame detection, strategic applications for detecting missile plumes, for instrumentation in space applications, for environmental applications such as water or air quality monitoring, and for defense applications to detect chemical or biological threats. Existing commercial UV photodetectors provide poor performance with peak responsivity in the ultraviolet range of less than 0.2 A/W.

Performance enhancement of the photodetectors is achieved by using functionalized multi-walled carbon nanotubes for better charge carrier collection efficiency and faster charge transport. The impact of the thickness of carbon nanotube network on the dark and photo current of the photodetectors is studied. Surface passivation using two polymers: PVA and PVP, is proposed to suppress the parasitic luminescence caused by defects in the metal oxides. Surface passivation is shown to improve the responsivity of the photodetector by a factor of hundred. The polymer properties that dictate the performance enhancement of photodetectors are evaluat-ed. Hollow nanospherical structures are explored to further improve the responsivity. Template free synthesis method for tin oxide hollow nanospheres using Ostwald ripening process is pre-sented. The responsivity of the photodetector fabricated with tin oxide hollow nanospheres shows nine hundred times improvement compared to the nanoparticle-based detector. Whisper-ing gallery mode resonance phenomenon is discussed to explain high responsivity of photodetec-tors fabricated using hollow nanospheres.

In this thesis, we have developed visible blind UV photodetectors with high responsivity. The application of focus in this work is UV photodetectors for biohazard detection in living spaces. The intrinsic fluorescence at 340 nm from microbes is exploited to detect microbes in the presence of ambient light. High performance UV photodetectors based on metal oxide nanostruc-tures are designed and fabricated. Three metal oxides: tin oxide, zinc oxide and gallium oxide are explored for the fabrication of high performance UV photodetectors.