ZnO is a remarkable semiconducting oxide material that presents opportunities in transparent electronics, UV photonics, nanoelectronics, and spintronics. A key element is to impose the desired functionality via heteroepitaxy and doping. In this talk, we will discuss the synthesis of epitaxial ZnO thin films and nanowires doped for charge and spin functionality. For spin functionality, the magnetic properties of transition metal doped epitaxial ZnO thin films will be described. For specific co-doping combinations, we find evidence for ferromagnetism with a Curie temperature approaching 300 K. The magnetization versus field behavior for an epitaxial Mn,Sn doped ZnO film shown in Fig. 1 clearly shows hysteresis, which is indicative of magnetism. Differences in zero field-cooled and field-cooled magnetization persists up to ~ 250 K. In doping for charge, the most significant issue is in achieving p-type conductivity. To this end, we will discuss recent studies of group V anion doping. In particular, the doping behavior of phosphorus in ZnO thin films grown by pulsed-laser deposition is examined. The transport properties of epitaxial ZnO films doped with 1 to 5 at.% P were characterized via room temperature Hall measurements. As-deposited films doped with phosphorus are highly conductive and n-type. The origin of the shallow donor level appears to be either substitution of P on the Zn site or formation of a donor complex. Annealing these phosphorus-doped films significantly reduces the carrier density, transforming the transport from highly conducting to semi-insulating. These results, shown in Fig. 2, indicate that the phosphorus-related donor defect is relatively unstable, and suggests the formation of a deep level upon annealing. The latter is consistent with phosphorus substitution on the O site yielding a deep level in the gap.
展开▼
