Thermal microcrack distribution control in GaN layers on Si substrates by lateral confined epitaxy

GaN epitaxial layers grown uniformly on Si substrates suffer from randomly distributed thermal cracks. The growth on prepatterned Si substrates is dem onstrated as an efficient way to control the geometrical distribution of th e thermal cracks. In order to study this effect and to find the maximum cra ck-free lateral dimension of a GaN patterned unit on Si, a simple procedure termed lateral confined epitaxy (LCE) was developed. This procedure confin es the growth of GaN to separate mesas of Si, which are defined on the Si s ubstrate prior to the growth. The growth is performed by a single, continuo us metalorganic chemical vapor deposition run. LCE enables the variation of mesa lateral size, while keeping the growth rate nearly unchanged. By perf orming a set of LCE growth runs of similar to0.7 mum GaN, on Si mesas of va rying lateral dimensions, we specified the maximum crack-free range of GaN on Si as 14.0 +/-0.3 mum, for that GaN thickness. A reduction of random cra ck density is observed with decreasing GaN pattern size and is explained in terms of shear-lag stress distribution. (C) 2001 American Institute of Phy sics.