Study of III-V Nitride and Semiconducting Metal-Oxide Based Chemical Sensors

Abstract

In this dissertation a series of high performance　III-V nitride compound and semiconducting metal-oxide based chemical sensors including Schottky diodes resistors and extended-gate field-effect transistors (EGFETs) are fabricated and studied III-V nitride compound semiconductors such as AlGaN- and GaN-based materials serve as sensing platforms Since these materials have larger band gaps the fabricated devices are suitable for high-temperature operation In addition Pt and Pd are used as sensing metals because of their good catalytic activity toward ammonia and hydrogen gases respectively On the other hand metal-oxide semiconductor such as NiO- and ZnO- based materials serve as a sensing membrane The NiO sensing membrane demonstrates excellent pH sensing and specific gas sensing characteristics good chemical stability and corrosion resistance The ZnO sensing membrane shows excellent performance for NO2 sensing Therefore the NiO-based material is suitable for high-performance pH sensing applications and both NiO- and ZnO-based materials can be used as specific gas sensing membranes Electrical characteristics and sensing performance of the studied gas sensors are investigated at different temperatures and gas concentrations Furthermore pH sensing properties and non-ideal effects of the studied NiO-based pH sensor are studied First a chemically electroless plated (EP) Pt/AlGaN/GaN Schottky diode-type ammonia sensor is fabricated and studied The thermionic emission (TE) equation is employed to characterize the current-voltage (I-V) behaviors of the studied EP device upon introduction of ammonia gases The Schottky barrier height extracted from the TE equation is found to be sensitive to ammonia gases under various concentrations Ammonia sensing behaviors of the studied EP device are investigated in terms of those diode parameters sensing responses and response times Second the hydrogen sensing characteristics of Pd/AlGaN/GaN Schottky diodes with nanostructures are investigated Pd/SiO2/AlGaN (metal/oxide/semiconductor) hydrogen sensors prepared by spin-coating SiO2 nanoparticles between Pd and AlGaN layers are fabricated Due to the observation of a better junction quality and a higher surface roughness hydrogen sensing properties of the studied device can be improved On the other hand a Pd pyramid-like nanostructure is successfully made by thermal evaporation and lift-off processes with PS nanospheres This structure can efficiently increase the surface-area-to-volume ratio which caused the more active adsorbing sites Analyses of the sensing properties of the studied devices with nanostructures at different temperatures and hydrogen concentrations are presented respectively Third NiO thin film-based extended-gate field-effect transistor (EGFET)-type pH sensors and a resistor-type gas sensor prepared by the radio-frequency (RF) sputtering process are fabricated and studied The influences of various sputtering conditions and post-annealing are investigated by I-V curves variation of studied EGFET-type devices when immersing in different pH buffer solutions Moreover a NiO thin film-based resistor-type gas sensor deposited on interdigitated electrodes is fabricated Hydrogen and ammonia sensing behaviors of the studied resistor-type device are analyzed and investigated at different temperatures Finally the nitride oxide (NO2) sensing performance of ZnO nanoparticles (NPs)-based sensors is demonstrated and investigated ZnO NPs are employed to the increase surface-area-to-volume ratio of the studied device which causes more active adsorbed sites Thus an enhanced sensing performance can be observed Experimentally the studied devices exhibits excellent sensing responses towards high NO2 concentration and a low detection limit at high temperatures Based on good results and compatibility of these sensing devices in this dissertation the studied devices are promising for the integration of high-performance sensor and micro-electro-mechanical-systems (MEMS)

Date of Award	2015 Jul 6
Original language	English
Supervisor	Wen-Chau Liu (Supervisor)