Investigation of ZnO nanorods for UV detection

Sammanfattning: In recent years, there has been increasing interest in ZnO semiconductors for optoelectronic application in the UV wavelength region due to its large exciton binding energy of 60 meV and wide bandgap energy of 3,37 eV at room temperature. One-dimensional ZnO nanostructures such as nanorods or nanowires have been considered as promising candidates for UV sensing and detecting applications owing to its high surface to volume ratio. In this thesis work 5 different types of UV photodetectors based on ZnO nanorods were fabricated successfully. The basic technique is to utilize a chemical solution synthesis method for forming ZnO nanorods on different types of substrate, and then fabricate simple metal semiconductor metal (MSM) and P-doped/N- doped (PN) photodetectors using the nanorods as UV detecting material. The MSM photodetectors are accomplished using interdigitated electrodes forming by the thin gold fingers on the desired substrates, while the PN photodetector were fabricated using ZnO nanorods sandwiched between a top metal contact and a heavy P-doped Si substrate. So far various lateral and vertical ZnO nanorods/nanowires with different dimensions (60 nm to 80 nm in diameter) and length (1 μm to 7 μm) have been synthesized. Also, the ZnO nanoflower (about 5 μm in height) arrays based on ZnO nanorods were demonstrated. The nanoflowers were mainly formed by three process steps. First a seed layer was spin coated on Si substrate, and then a positive photoresist layer with thickness of 1.5 μm was patterned for allowing the growth of ZnO nanorods precisely in desired locations. Finally the photoresist was stripped away. The structural and composition properties of the ZnO nanostructures (seed, nanorods and nanoflowers) were inspected and characterized by implement of optical microscope, atomic force microscopy (AFM), scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS). The device performance was characterized by current-voltage (I-V) characteristics in the dark, visible light and UV light, spectral photoresponse and time response as UV light switching on and off. Demonstration of cost-effective ZnO nanorods UV photodetectors through this work reveals a promising potential for extending nano- and micro-technologies beyond the lab bench for future commercialization of such components, thus facilitate entry to new markets.