Zinc Oxide MESFET Transistors
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
Zinc oxide is a familiar ingredient in common household items including sunscreen and medicines. It is, however, also a semiconductor material. As such, it is possible to use zinc oxide (ZnO) to make semiconductor devices such as diodes and transistors. Being transparent to visible light in its crystalline form means that it has the potential to be the starting material for so-called 'transparent electronics', where the entire device is transparent. Transparent transistors have the potential to improve the performance of the electronics currently used in LCD display screens. Most common semiconductor devices require the material to be selectively doped with specific impurities that can make the material into one of two electronically distinct types – p- or n-type. Unfortunately, making reliable p-type ZnO has been elusive to date, despite considerable efforts worldwide. This lack of p-type material has hindered development of transistors based on this material. One alternative is a Schottky junction, which can be used as the active element in a type of transistor known as a metal-semiconductor field effect transistor, MESFET. Schottky junctions are traditionally made from noble metal layers deposited onto semiconductors. Recent work at the Canterbury University has shown that partially oxidised metals may in fact be a better choice, at least to zinc oxide. This thesis describes the development of a fabrication process for metal-semiconductor field effect transistors using a silver oxide gate on epitaxially grown zinc oxide single crystals. Devices were successfully produced and electrically characterised. The measurements show that the technology has significant potential.