Structural characterization of high temperature AlN intermediate layer in GaN grown by molecular beam epitaxy

Transmission electron microscopy has been used to study the structural qual ity of GaN grown on sapphire by plasma assisted molecular beam epitaxy usin g high temperature AlN intermediate layers with different thicknesses. The introduction of an AlN intermediate layer with an optimum thickness is obse rved to minimize the density of dislocations reaching the overgrown GaN sur face. In this sample, the measured threading dislocation density reaching t he surface of 1 x 10(10) cm(-2) resulted to be seven times lower than that of a reference sample, without any AlN interlayer. The bending at the GaN/A lN interface and following interactions between dislocations have been obse rved in cross-sectional transmission electron micrographs. This fact explai ns the decrease of dislocation density reaching the GaN surface. (C) 2001 P ublished by Elsevier Science B.V.