Direct Growth of A-Plane GaN on R-Plane Sapphire Substrate by Metalorganic Vapor Phase Epitaxy

We have investigated a direct growth of non-polar a-plane GaN on r-plane sapphire substrate by metalorganic vapor-phase epitaxy (MOVPE). We found that high-density nucleation of GaN islands was grown on r-plane sapphire substrate at an initial stage of high temperature growth without a buffer layer, which resulted in a flat surface of the a-plane GaN. We also studied an effect of growth conditions on surface morphologies and the growth features of the a-plane GaN. The results showed that inverse-triangular pits surrounded with facets were formed at a relatively high V/III ratio, and the lateral growth rate along the c-axis direction was enhanced at a relatively low V/III ratio.

In the present paper we propose to extend the selective epitaxy of GaN to the lateral overgrowth and to take advantage of the growth anisotropy to produce strain free GaN crystals. After filling the openings in a dielectric mask by selective epitaxy, lateral overgrowth occurs reflecting the growth anisotropy. This allows the fabrication of samples with non-planar geometry. The selective epitaxy was achieved by metal organics vapour phase epitaxy (MOVPE) whereas lateral overgrowth until island coalescence was carried out either by MOVPE or halide vapour phase epitaxy (HVPE). A GaN epitaxial layer is first grown using atmospheric pressure metalorganic vapour phase epitaxy on sapphire. The dielectric film is silicon nitride. The openings are achieved using standard photolithographic technology. These openings reveal free GaN surface and are used for epitaxial regrowth by MOVPE, and then by HVPE.


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