The Growth of Metal Oxide Structures and their Application for Optoelectronic and Sensing Devices

Abstract

The main goal of this dissertation is the synthesis and application of metal oxide nanostructure The dissertation is divided into three sections due to different kind of material and application The first one is the investigation of p-type CuO nanowires (NWs) and application for field emitters In the beginning of this dissertation the growth of p-type CuO NWs by thermal oxidation of Cu film deposited on CuO/glass template is reported It was found that we could achieve a higher NW density longer average NW length by increasing the Cu film thickness The sample with higher NW density has low turn-on field and large field enhancement factors (β) Furthermore it was found that we could improve the field emission ability and reduce the turn-on field from by simply illuminating the samples with ultraviolet (UV) light In order to enhance the field emission properties further hybrid Cu/CuO NWs are fabricated by reduction of CuO NWs It was found that the surfaces of CuO NWs partially transformed into Cu via rapid thermal annealing (RTA) at 270 °C in H2 ambiance forming hybrid Cu/CuO NWs The results show that hybrid Cu/CuO NWs efficiently reduce turn-on field and increase β values Furthermore a novel three-dimensional (3-D) structure with CuO NWs is demonstrated Cu rods with diameter of 10 μm on a flexible silicon substrate were fabricated using through silicon via (TSV) process and chemical mechanical polishing (CMP) 3-D CuO NWs were then grown vertically and laterally on the top and sidewall of the Cu rods via heat treatment in air The sample performs great field emission properties through above fabrications The 3-D CuO NWs are suitable for future applications that require a flexible substrate Second the growth and analysis of n-type monoclinic Ga2O3 (β-Ga2O3) sensors are studied β-Ga2O3 NWs were synthesized via a vapor-liquid-solid mechanism by heating a GaN/sapphire template It was found that the conductivity of the β-Ga2O3 NW humidity sensors increased monotonically when the relative humidity (RH) was increased To determine the relationship between UV light and humidity sensing properties the humidity was measured with and without UV illumination and the UV photoresponse was measured at various RH values respectively On the third part of this dissertation metal oxide devices integrated with interdigitated back contact (IBC) photovoltaic (PV) cell as a self-powered device is demonstrated Ta2O5/a-IGZO thin film transistor (TFT) was fabricated on the rear side of crystalline-Si IBC PV cell by vertical stacking method The connection of a-IGZO and IBC PV cell was linked by depositing Al to form a single chip as the function of self-powered solar device This device exhibits switch property of on/off status under illuminated or dark environment Moreover self-powered multi-functional sensors were fabricated by integrating an IBC PV cell with a vertically stacked structure into a single chip The IBC PV cell was vertically connected with WO3 thin film humidity sensor and Ga2O3 thin film PD in parallel The measured current of WO3 thin film humidity sensor increased monotonically when the RH was increased The cutoff wavelengths of WO3 and Ga2O3 thin-film were around 370 and 250 nm respectively which can be applied to dual band PDs

Date of Award	2016 Jul 5
Original language	English
Supervisor	Shoou-Jinn Chang (Supervisor)