Fabrication And Properties Of ZnO Based Heterostructures And Related Field Effect Transistors

Zinc oxide (ZnO) is a direct wide band gap semiconductor with a large exciton binding energy of60meV. Owing to its superior optoelectronic properties, ZnO has the potential for transparent and flexible electronics for displays and other devices, like violet-blue light emitting diodes, ultraviolet photodetectors and shortwavelength exciton-based lasers. The lack of stable and reproducible p-type materials restrict the application of ZnO. So researchers have concentrated on the investigation of intrinsic physical properties of ZnO. However, the heterostructure can be used to take advantage of the superior properties of ZnO. In this work, the following aspects have been studied systematically:fabrication process of ZnO-based devices has been proposed and investigated; electrical and photoluminescencent properties of heterostrustures with2DEG in the interface; fabrication of HFET, measurement and study of its electrical properties. The article results include:1. The ZnO-based devices’fabrication process has been studied and investigated systematically. Processes such as lithography, electro beame vaporation and rapid thermal process for alloying processes have been investigated. Rapid thermal process has been employed to improve the Ni/Au contact to ZnO film. Key parameters of process were achieved, and ZnO-based TFT has been fabricated. This study lays a foundation for further ZnO-based optoelectronic devices fabrication.2. Growth and Properties of ZnMgO/ZnO heterostrustures has been studied. Carrier concentration of ZnMgO/ZnO heterostrustures at room temperature was7x1017cm-3, with mobility of1516cm2/V-s. The formation of two-dimensional electron gas (2DEG) in the interface and its electrical properties has been studied. These properties include the layer thickness dependence of sheet carrier concentration, and temperature dependence of mobility. Reported that the formation of2DEG was the combined action of piezoelectric polarization and spontaneous polarization3. ZnO/ZnMgO heterostructure field-effect transistor (HFET) was fabricated with a150-nm-thick SiO2gate dielectric. Current-voltage characteristics were measured at room temperature, which showed the transconductance was180μS/mm and mobility was182cm2/Vs. The property was limited by leakage current through the SiO2gate insulator. However at low temperature, the property was improved due to the reduced leakage current.