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Defect reduction via confined epitaxial growth of GaN

III-N materials continue to play a significant role in a range of technologies from rf electronics to visible and UV emitters and detectors. This is true despite a heavy population of extended defects in the active regions of these devices, which degrade the operation, potential performance, and reliability of such devices. One approach to improve this situation involves the use of confined epitaxy to reduce strain in the selectively grown epitaxial material and encourage dislocation annihilation near the interface between the continuous epitaxial layer and the confined epitaxy region, thus reducing dislocation density in the device active region grown by confined epitaxy. This approach is similar to lateral epitaxial overgrowth in the use of a patterned substrate, but in an effort to enable vertical devices and utilize the substrate as part of the device, the confined epitaxial method does not involve lateral growth. Using this technique, we have developed materials with dislocation densities reduced by a factor of 10 and stress reductions of 50% compared to continuous layers [1]. These improvements are theorized to be the result of the ability of the confined epitaxy columns to twist and flex to accommodate strain without a need for extended defect formation [2]. Taking advantage of the improved material, two-color UV imagers have been fabricated using this approach [3].