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Successive selective growth of semipolar (11-22) GaN on patterned sapphire substrate

Thanks to the use of two successive selective growths by metal organic chemical vapor deposition reactor, high quality semipolar (11-22) GaN with a homogenous defect repartition over the surface was achieved. The procedure starts with a first selective growth on a patterned sapphire substrate, leading to continuous stripes of three dimensional (3D) GaN crystals of low defect density. Then, a second selective growth step is achieved by depositing a SiNx nano-mask and a low temperature GaN nano-layer on the top of the GaN stripes. Hereby, we demonstrate an original way to obtain a homoepitaxial selective growth on 3D GaN crystals by taking advantage of the different crystallographic planes available. Basal stacking faults (BSFs) are generated during this second selective growth but could be eliminated by using a three-step growth method in which elongated voids are created above the defective area. For a fully coalesced sample grown using the 2 step method, dislocation density of 1.2 × 108 cm−2 and BSFs density of 154 cm−1 with a homogenous distribution have been measured by cathodoluminescence at 80 K. Consequently the material quality of this coalesced semipolar layer is comparable to the one of polar GaN on c-plane sapphire.