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We demonstrated how annealing of the sputtered AlN buffer layer (sp‐AlN) on r‐plane sapphire could be used to produce a high‐crystalline‐quality a‐plane GaN (a‐GaN). The sp‐AlN with large grains was confirmed by annealing at 1600 °C in N2 ambient, consequently its crystalline orientation and quality were significantly improved. Moreover, it was found that a‐GaN grown on annealed sp‐AlN showed better crystalline quality, including a reduction of basal stacking fault density, than a‐GaN grown on untreated sp‐AlN (as sputtered). The implication is that the a‐GaN growth method using annealed sp‐AlN is an effective way to obtain high crystalline quality.

Typical multi quantum well (MQW) grown on nonpolar a-plane GaN templates shows many pits composed of several semipolar planes, and these pits emit at different wavelengths due to the variation of indium incorporations into the QW. In this study, a surface-recovery GaN layer and hightemperature grown barrier were introduced to improve the a-plane MQW quality. We succeeded in decreasing the pits prior to the MQW growth and improving the interfaces of MQW. The structural and optical properties of the MQW were significantly improved.

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