Ion beam analysis of epitaxial (Mg, Cd)_xZn_(1―x)O and ZnO:(Li, Al, Ga, Sb) thin films grown on c-plane sapphire

摘要

In this study ZnO thin films, nominally undoped, doped with Li, Al, Ga and Sb and alloyed with Mg and Cd grown epitaxially on c-plane sapphire by pulsed laser deposition (PLD) were investigated. In order to correlate the optical and electrical properties, e.g. the band gap energy and carrier concentration, to the elemental composition, the films were analyzed by RBS, PIXE and PIGE using He~+ and H~+ ion beams. It was found that the element transfer from the PLD target to the film differs significantly for the individual doping and alloying elements, with concentration ratios between film and target ranging from ～4% for Li and Cd to ～400% for Ga. In general, the films exhibited a metal to oxygen ratio of 1:1, only the ZnO:Li films were slightly oxygen deficient. Furthermore, the crystalline quality of the films was investigated using ion channeling. The nominally undoped ZnO films which were deposited with low-temperature in-terlayers for lower lateral stress showed a normalized minimum RBS yield of χ_(min) = 3.3% under channeling conditions. Whereas the incorporation of isovalent alloying atoms into the ZnO films leads to a slight degradation of the crystalline quality only, doping degrades the crystalline quality remarkably, even at low dopant concentrations.