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A Microscopic Evaluation of the Surface Structure of OMVPE Deposited α-GaN Epilayers

  • G. S. Rohrer (a1), J. Payne (a1), W. Qian (a1), M. Skowronski (a1), K. Doverspike (a2), L. B. Rowland (a2) and D. K. Gaskill (a2)...

Abstract

The surface structure of organometallic vapor phase epitaxy (OMVPE) grown α-GaN films was investigated using optical and scanning force microscopy (SFM). Optical microscopy shows that the surface is decorated with several different types of faceted features that have lateral dimensions of 10 to 75 μm and occur with a density of approximately 104/cm2. SFM images show that on the flat regions of the surface, single diatomic layer steps, 2.6 Å high, are straight, evenly spaced (at 500 to 1500 Å intervals), and oriented along á101ñ directions. The SFM images also show that the regular step patterns are often interrupted by faceted growth hillocks, 0.8 to 5 μm in diameter and 120 to 400 Å high, that occur with a density of 106/cm2. An open-core screw dislocation with a Burgers vector of 5.2 Å occurs at the center of each hillock and is a source for spiral steps. Other dislocations are also observed to intersect the flat regions of the surface and create a step, but these have smaller Burgers vectors, do not form spirals, and do not have open cores. Based on these observations, we conclude that thick OMVPE GaN films grow by a combination of the layer-by-layer and spiral growth mechanisms.

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