GaN-based epitaxy on silicon: stress measurements

We present an in situ method for the determination of the stress in GaN layers on hetero‐substrates, in particular Si, via measuring the wafer curvature. For device application it is essential to obtain stress free low‐curvature layers. With our in situ method we directly observe the evolution of strain and can identify the sources of strain and the efficiency of strain compensating layers. We find a strong increase in tensile stress with increasing Si doping up to 0.18 GPa for a 1018 cm−3 Si doping concentration. This can be significantly reduced by an appropriate buffer layer growth scheme. The compensation of tensile thermal stress by introducing AlN interlayers to avoid cracking of GaN on Si is in situ investigated. We find that the impact of undoped AlN interlayers is independent of growth temperatures Tgrowth up to Tgrowth > 1000 °C. A linear dependence of strain reduction on AlN interlayer thickness up to a thickness of 12 nm is observed. Using appropriate growth schemes more than 6 μm thick crack free high quality GaN layers on Si were grown. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)