Both non-polar a-plane GaN and ZnO films grown on (0 0 1) LaAlO3 (LAO) substrates consist of orthogonal domain structures. The influence of inserted underlying ZnO on the growth behavior of subsequently grown GaN has been investigated by using transmission electron microscopy and scanning electron microscopy. The size of GaN domains is increased after the incorporation of ZnO underlayer. GaN domains deposited on ZnO/(0 0 1) LAO extend along an in-plane preferential direction which has about 43-45 degrees from [0 0 0 1](GaN). The underlying ZnO results in overgrown GaN domains to locally form r-plane twin structures. (C) 2009 Elsevier B.V. All rights reserved.