Northwestern researchers have developed a technique to deposit biaxially oriented ZnO thin films on amorphous substrates. Well textured ZnO thin films on low-cost substrates are of interest for ZnO-based devices and as “substrates” for subsequent growth of devices based on AlN, GaN, InN, such as light-emitting diodes and lasers. With continued improvement in the crystal orientation of ZnO, new low-cost devices should become possible.
Biaxially oriented ZnO films have been successfully grown on glass and thermally oxidized silicon by a technique known as dual magnetron oblique sputtering (DMOS). DMOS was originally developed at Northwestern to create oriented yttria stabilized zirconia. The technique uses reflected ions from two dc magnetron sputter sources positioned at oblique angles to the substrate normal to create in-plane orientation in the deposited film. It has been found that orientation in ZnO films is dependent on the incident angle of the incoming ions. The degree of orientation is highest when incident ions have an incoming angle of ~30° from the surface normal, based on x-ray data. It has also been found that post-deposition annealing substantially increases the orientation; resulting in a 60% increase in degree of orientation. Substrate heating during deposition has a detrimental affect on the orientation.
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