Colloidal nanoparticles have great potential in making high performance photodetectors as 1) their high surface area to volume ratio contributes to better absorption of light than bulk material does, 2) their 3-D quantum confinement effects enable continuous tuning of the detection wavelengths by changing the size of nanoparticles, 3) their high quantum efficiency benefits optical to electrical signal conversion, 4) their solution-based synthesis is well compatible with additional surface coating processes to improve the materials' performance, and 5) they are independent of the substrate onto which they are ultimately deposited, eliminating the lattice matching requirements inherent in the growth of crystalline semiconductors.

In this thesis, high performance, large area, visible blind and wavelength selective planar/vertical/heterojunction organic and inorganic hybrid UV photodetectors based on polyvinyl-alcohol (PVA) coated ZnO colloidal nanoparticles created by top-down wet-chemical etching method onto different functional substrates for different applications were studied for the first time. With PVA surface passivation, suppressed parasitic green photoluminescence and enhanced UV emission of ZnO colloidal nanoparticles were achieved, which contributed to the high performance of the frbricated photodetectors.

The planar PVA coated ZnO nanoparticles MSM photodetector with finger contacts fabricating by normal lithography and wet-etching method was done for the first time. The MSM photodetector has the highest normalized detectivity and response speed product compared with other reported photodetectors based on ZnO nanomaterials till the time of writing this thesis. Lowpass and wavelength selective bandpass alternative spectral response of photoconductor and p-GaN/ZnO heterojunction photodiode were achieved relying on illuminating directions through GaN or ZnO. Reproducibility, distribution uniformity, sensitivity dependence of substrates, and aging effect of these photodetectors has been studied. Advantages of wavelength selective photodetectors on functionalized substrates were demonstrated by their applications in a compact semiconductor based bio-detection system with 90º and 180º setup respectively and a scintillator based multilayer alpha particle sensor. Successful experience was expanded to another metal oxide (In₂O₃) with targeted peak response moving towards the visible light direction.