Effects of defects on the electrical and optical properties of ZnO thin films

Zinc oxide is a wide band gap semiconductor with potential applications in optoelectronic devices. The greatest challenge for these applications is to fabricate reliable and stable p-type ZnO thin films. There exist many reports of p-type conductivity in ZnO films doped with group V elements.Ü However, little understanding of the role of defects, either native or induced by doping, on the onset of p-type conductivity and on the degradation of optical properties. In this talk, we will demonstrate the effects of crystal defects on the optoelectronic properties of p-type ZnO epitaxial thin films. We will show that the interplay between dopants and extended defects such as dislocations and stacking faults is fundamentally important for the fabrication of p-type ZnO. ZnO thin films doped with nitrogen, phosphorus and antimony were grown by pulsed laser ablation. We will show that dislocations can, under certain conditions, aid the formation of shallow acceptors. ThÜe role of dislocations on the dopant solubility, electrical transport properties and photoluminescence will be addressed. We will also show that depending on the oxygen chemical potential, different defect levels can be introduced in the band-gap. These defects result in various optical transitions that can provide useful information on the donors and acceptors formed. Finally, issues of homoepitaxy and p-n junction fabrication will be presented.Ü From these studies, we conclude that the fabrication of p-type ZnO films is trivial, however, a p-type epitaxial thin film with high structural quality is challenging.Ü