Defects in a nitrogen-implanted ZnO thin film

Defects in a nitrogen implanted and thermally annealed zinc oxide thin film (n-type conducting) and reference samples were studied. Space charge regions realised by fabrication of semitransparent palladium Schottky contacts enabled the application of capacitance spectroscopic methods and photo - current measurements. We report on the formation of a deep level, in the following labelled TN1. It is 580 meV below the conduction band edge, probably related to nitrogen, and must be distinguished from the well known intrinsic deep level E4 at almost equal energetical depth. Capacitance measurements in combination with optical excitation, conducted at different temperatures, as well as photo-current measurements revealed the existence of two states approximately 60 meV and 100 meV above the valence band edge for the nitrogen implanted sample. These states cause an acceptor compensation degree larger than 0.9. The thermal emission of holes from these states into the valence band was observed by optical deep level transient spectroscopy.