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 demonstrated as an efficient way to control the geometrical distribution of the thermal cracks. In order to study this effect and to find the maximum crack-free lateral dimension of a GaN patterned unit on Si, a simple procedure termed lateral confined epitaxy (LCE) was developed. This procedure confines the growth of GaN to separate mesas of Si, which are defined on the Si substrate prior to the growth. The growth is performed by a single, continuous metalorganic chemical vapor deposition run. LCE enables the variation of mesa lateral size, while keeping the growth rate nearly unchanged. By performing a set of LCE growth runs of similar to0.7 mum GaN, on Si mesas of varying 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 crack density is observed with decreasing GaN pattern size and is explained in terms of shear-lag stress distribution. (C) 2001 American Institute of Physics.