Epitaxial ZnO films were hydrothermally grown in water at 90C on MgAl2O4 (111) substrates. A lateral epitaxial overgrowth method was used to reduce threading dislocations at the boundaries of crystal mosaic in the epitaxial films. In the optimized ZnO lateral epitaxial overgrowth with a ratio of window to wing (3:10), dislocations arose from two regions, i.e. unmasked window and coalescence of masked wings while they were seldom present in the wing area. The average density of dislocation was significantly reduced from 1.4 x 109 to 2.3 x 108/cm2. A double lateral epitaxial overgrowth process was applied for further dislocation reduction with the 3μm-wide unmasked region centered on the coalesced wings region from the first lateral epitaxial overgrowth. The average density of dislocation was found not to decrease by another order of magnitude but only to 1 x 108/cm2 because new threading dislocations were created at the coalescence of wings from the first lateral epitaxial overgrowth.

Reduction of Threading Dislocations in Hydrothermally Grown ZnO Films by Lateral Epitaxial Overgrowth. Y.B.Zhang, G.K.L.Goh, S.Li: Thin Solid Films, 2010, 518[24-1], e104-6