Stress and Defect Distribution of Thick GaN Film Homoepitaxially Regrown on Free-Standing GaN by Hydride Vapor Phase Epitaxy

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A 220-μm-thick Gallium nitride (GaN) layer was homoepitaxially regrown on the Ga-polar face of a 200-μm-thick free-standing $c$-plane GaN by hydride vapor-phase epitaxy (HVPE). The boundary of the biaxial stress distribution in the GaN substrate after regrowth was clearly distinguished. One half part, the regrown GaN, was found to be more compressive than the other half part, the free-standing GaN. Additionally, the densities of the screw and mixed dislocations reduced from $2.4 \times 10^{7}$ to $6 \times 10^{6}$ cm-2 after regrowth. Furthermore, the yellow band emission almost disappeared, accompanied by a peak emission at approximately 380 nm related to the edge dislocation was under slightly improved in regrown GaN. We conclude that the reduction of the dislocation defects and Ga vacancies and/or O impurities are the two main reasons for the higher compressive stress in the regrown GaN than in the free-standing GaN, causing the curvature of the GaN substrate to be twice concave after regrowth.
2010-09-25