Influence of LT-AlN buffer layers on density of threading dislocation in AlGaN layers

To assess the influence of low temperature (LT) AlN buffer layers on the density of threading dislocations, we deposited multilayer structures consisting of AlN and AlGaN using metal organic chemical vapor deposition. We used two types of composite substrate in this study: (1) ELOG GaN/sapphire, and (2) sapphire. The resulting multilayer structures were examined in cross section by transmission electron microscopy. We show that the deposition of low temperature AlN buffer on highly perfect ELOG GaN leads to defective AlN/GaN interfaces. Some of the dislocations associated with these interfaces evolve into threading dislocations in AlGaN layers. We also demonstrate that multilayer of AlN buffers are only moderately effective in reducing the density of TDs into overgrown AlGaN layers.