Annealing Effect on GaN Buffer Layer Surface

Abstract

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 H 2 þ N 2 gas mixture and the thickness of the buffer layers. The correlation between this observation and the AFM images indicates that H 2 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 N 2 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.

Understanding GaN nucleation layer evolution on sapphire

“…This roughened growth mode results in an attenuation of the reflectance signal. A similar reduction in the reflectance signal due to roughness has also been observed as the NL is annealed [30,41,42]. The root-mean-square (RMS) surface roughness, s RMS , will attenuate the surface reflectivity, R, by…”

“…Optical reflectance has previously been used to investigate GaN film evolution [30,[38][39][40][41][42][43][44]. In these optical reflectance studies, particular attention has been paid to the NL evolution [30,38,41,44] and the 3D roughening to 2D smoothing transition at high T [38][39][40]42,43].…”

“…In these optical reflectance studies, particular attention has been paid to the NL evolution [30,38,41,44] and the 3D roughening to 2D smoothing transition at high T [38][39][40]42,43]. From these studies and accompanying AFM images, correlations have been established between the reflectance signal and the GaN morphology.…”

“…From these studies and accompanying AFM images, correlations have been established between the reflectance signal and the GaN morphology. For example, Halidou et al have shown that annealing a GaN NL in a mixed H 2 /NH 3 results in a rough NL with larger GaN nuclei, while annealing the NL in a mixed N 2 /NH 3 flow results in smaller GaN nuclei [41]. In…”

Influence of the nucleation layer morphology and epilayer structure on the resistivity of GaN films grown on c-plane sapphire by MOCVD

“…[5][6][7][8][9][10]), but only a few of these describe its influence on the GaN NL [11,12]. Halidou et al [11] presented AFM images of NL grown using different carrier gas. The authors observed similar relations between carrier gas and and NL surface morphology as presented in this paper.…”