ZnO-based materials, nanostructures, and devices have attracted increasing attention in recent years. ZnO has a direct energy bandgap (Eg ≈ 3.3 eV at room temperature). It can be alloyed with CdO and MgO to form the ternaries CdxZn1-xO and MgxZn1-xO, extending the direct energy band from 2.8eV to 4.0eV. Through proper doping, ZnO can be made transparent and conductive, semiconducting, piezoelectric, or ferromagnetic. Furthermore, it is possible to utilize ZnO based multilayer structures and ZnO nanostructures to design and construct completely new integrated devices, such as tunable RF devices and multifunctional sensors.
We have grown high quality epitaxial ZnO films on r-plane sapphire substrates by MOCVD. The non-polar a-plane ZnO based multilayer structures have been used to demonstrate various new devices, including optically addressed high contrast and high speed UV modulator, high speed MSM photoconductive type UV detector, ZnO Schottky diode photodetector, and high frequency low loss SAW filters, BAW resonators, monolithically integrated tunable SAW sensor (MITSAW), wireless UV SAW sensor, nano-SAW and nano-BAW sensor. Epitaxial MgxZn1-xO films, with Mg composition up to 35% have been grown on r-plane sapphire substrates. Schottky and non-alloyed ohmic contacts to these films have been developed. The selective MOCVD growth technology has been developed to fabricate ZnO nanotips. In this talk, our research results of the MOCVD growth, physical properties, and device applications of ZnO-based materials and nanostructures will be presented. Recent progress in the areas of ZnO nanotip/GaN blue LEDs, ZnO nanostructure-based biochemical sensors, ZnO and MgxZn1-xO transparent FETs, and ZnO TCO plus nanotip-based dye sensitized solar cells, etc., will also be discussed.
ACKNOWLEDGEMENTS: The work has been sponsored by NSF, AFOSR, ARO, and NJ Excellence Center Program.