I. Halidou

Annealing Effect on GaN Buffer Layer Surface

We investigate the effect of annealing parameters (carrier gas, duration) on GaN buffer layers grown by metalorganic vapor phase epitaxy. The samples were characterized in situ by a laser reflectometry (LR) set-up with a He–Ne laser beam and ex situ by atomic force microscopy (AFM). The reflectivity decreases when the temperature is about 1050 °C. This fact depends on the hydrogen flow rate in the H2 + N2 gas mixture and the thickness of the buffer layers. The correlation between this observation and the AFM images indicates that H2 generates a mass transport on the substrate surface and a three-dimensional (3D) mode surface morphology for thick buffer layers. For thin buffer layers this phenomenon is limited and the sample surfaces have a two-dimensional aspect (2D) similar to that obtained under N2 rich annealing ambient. Under this ambient, no surface transformation is observed for longer annealing duration, which means that all the surface transformations occur during the temperature ramp between 600 and 1050 °C.