Printed Schottky Diodes based upon Zinc Oxide Materials

Abstract: The aim of this master thesis was to develop a process for fabricating Schottky diodes, using techniques that are suitable for cheap large volume mass production e.g. printing, with tetrapod structured ZnO as the semiconductor. Part of the work involved selecting suitable metals for ohmic and Schottky contact and identification of a binder that can be used for dispersion of the Zinc Oxide (ZnO). ZnO is a II-VI compound semiconductor with a wide band gap (3,4 eV). The Schottky diode is used as a rectifier. A rectifier serves the purpose to turn Alternating Current (AC) to Direct Current (DC). The Schottky diode should only conduct current in the forward direction, in the reverse direction the current should be blocked. In this thesis printed diodes were used to construct different types of rectifiers for example half wave rectifiers and full wave rectifiers. Aside from electrical properties, adhesion properties have also been investigated. Adhesion was showed to depend on not only the choice of binder, but also UV-dose and annealing temperature. Aluminum and silver together with ZnO proved to be the best materials combination with a rectification ratio up to 105−106. Different sizes of Schottky diodes were printed and the smaller diodes with an area of 0,5x0,5mm^2 performed best as a half wave rectifiers while the larger size,1x1mm^2, performed best as a full wave rectifier.