Low-temperature (LT) AlN interlayers can be applied to reduce the tensile stress and cracks in thick GaN layers on Si. Here, we present in X-ray diffractometry study revealing the influence of metalorganic chemical vapor phase deposition parameters on stress relaxation by these interlayers. The degree of stress relaxation is observed to strongly depend on interlayer deposition temperature. At low temperatures, LT-AlN grows incoherently on GaN, which leads to a temperature-dependent partial decoupling of stress and also to a decoupling of the GaN layers separated by the interlayers. We further observe a Ga incorporation into the LT-AlN interlayers dependent on growth temperature and Al-content of AlGaN layers grown on top of LT-AlN layers. By introducing LT-AlN interlayers a GaN X-ray diffractometry rocking curve FWHM of the (0 0 0 2) reflection of 400 arcsec for 3 mum thick crack-free layers is achieved. (C) 2002 Elsevier Science B.V. All rights reserved.