It was noted that GaN layers, grown onto Si(111) substrates, suffered from high tensile stresses that could lead to cracking at layer thicknesses exceeding 1μm. Also, the high dislocation density of GaN layers grown onto Si(111) was detrimental to device performance. It was shown here that a step-graded AlGaN buffer layer could compensate the tensile stress, thus avoiding cracking, and simultaneously reduce the dislocation density. An additional SiNx interlayer in the GaN layer further reduced the dislocation density to some 108/cm2. Weak-beam dark-field transmission electron microscopy was used to study the dislocation reduction in cross-sectional samples and to compare the step-graded AlGaN buffer layer structure with a continuously graded one.

Dislocation Reduction in MOVPE Grown GaN Layers on (111)Si using SiNx and AlGaN Layers. M.Haeberlen, D.Zhu, C.McAleese, M.J.Kappers, C.J.Humphreys: Journal of Physics - Conference Series, 2010, 209[1], 012017