Novel Devices Using Multifunctional ZnO and Its Nanostructures

Zinc oxide ZnO is a promising wide band gap semiconductor. It has a direct energy band gap, Eg of 3.3eV at room temperature. ZnO 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, it also can be made transparent and conductive, piezoelectric, or ferromagnetic. ZnO based single crystal nanostructures can be grown at relatively low temperature on various substrates. In this paper, we report new devices by using ZnO based multilayers and nanostructures. We have grown high quality epitaxial ZnO and MgxZn1-xO films on r-plane sapphire substrates by metal organic chemical vapor deposition MOCVD. The ZnO based semiconducting and piezoelectric multilayer structures are used to demonstrate various devices, including wireless SAW UV detectors and monolithically integrated tunable phase shifters. Single crystal ZnO and MgxZn1-xO nanotips are grown on various substrates, including Si, GaN, glass, and metal, used for new light emitting diode LED devices. The nanotips have a diameter of 60 nm and are oriented along the c-axis, normal to the growth plane. We have developed novel LED structures by integrating ZnO nanostructures on top of a GaN LED to enhance light extraction efficiency.