Dislocation reduction in MOVPE grown GaN layers on (111)Si using SiNx and AlGaN layers

Abstract

Growth of GaN on Si(111) potentially enables cost efficient manufacturing of optoelectronic devices due to the possibility of using cheap large area substrates. However, GaN layers grown on Si(111) substrates suffer from high tensile stress that can lead to cracking at layer thicknesses exceeding 1 μm. Another challenge is the high dislocation density of GaN layers grown on Si(111) which is detrimental to device performance. In this paper we show that a step graded AlGaN buffer layer can compensate tensile stress, avoiding cracking, and at the same time reduce the dislocation density. An additional SiNx interlayer in the GaN layer is shown to further reduce the dislocation density down to the high 108 /cm2. Weak beam dark field TEM was used to study the dislocation reduction in cross sectional samples and for comparison of the step graded AlGaN buffer layer structure to a continuously graded one. STEM ADF was used to determine the exact location of dislocation bending with respect to the position of the interface.