Aqueous lateral epitaxy overgrowth of ZnO on (0001) GaN at 90AC: Part I. Increasing the critical thickness

Thick, epitaxial ZnO thin films have been grown on (0001) GaN buffered Al2O3 substrates using an aqueous solution at 90AC. Films with improved structural, optical and electrical characteristics, were grown using a lateral epitaxial overgrowth (LEO) method. Different photoresist masks were used to enable LEO. The masks included linear windows and two different hexagonal arrays of circular windows. Films that exceeded a critical thickness mechanically failed through buckling, consistent with the large compressive stresses expected due to the mismatch of the ZnO lattice with the underlying GaN substrate. It was shown that improved mechanical stability could be achieved using the LEO method. Without LEO, a film thickness no greater than 4Akm could be grown without buckling. The critical thickness could be increased to 10Akm using linear windows, whereas a critical thickness of 50I14m was achieved with one array of circular windows, and 80Akm for a second array. The two different arrays of circular windows differed relative to their orientation on the substrate. It was also shown that the critical thickness increased with increasing distance between the growth windows. Optical transmission, micro-photoluminescence and Hall Effect measurements showed that the LEO method also results in improved optoelectronic properties.