Reduction of threading dislocations in hydrothermally grown ZnO films by lateral epitaxial overgrowth

Epitaxial ZnO films have been hydrothermally grown in water at 90 degrees C on MgAl2O4 (111) substrates. A lateral epitaxial overgrowth (LEO) method was utilized to reduce threading dislocations at the boundaries of crystal mosaic in the epitaxial films. In the optimized ZnO LEO 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 10(9) to 2.3 x 10(8) cm(-2). A double LEO process was applied for further dislocation reduction with the 3 mu m-wide unmasked region centered on the coalesced wings region from the first LEO. The average density of dislocation was found not to decrease by another order of magnitude but only to 1 x 10(8) cm(-2) because new threading dislocations were created at the coalescence of wings from the first LEO. (C) 2010 Elsevier B.V. All rights reserved.