Annihilation and Regeneration of Defects in (1122) Semipolar AlN <i>via</i> High-Temperature Annealing and MOVPE Regrowth
Li Chen, Wei Lin, Hangyang Chen, Houqiang Xu, Chenyu Guo, Zhibin Liu, Jianchang Yan, Jie Sun, Huan Liu, Jason X. Wu, Wei Guo, Junyong Kang, Jichun Ye
Abstract
Semipolar III-nitrides have attracted great attention due to their weak polarization field for optoelectronic devices. High-quality AlN is a perfect template in the epitaxial growth of AlGaN-based ultraviolet optical devices. In this work, (112̅2) semipolar AlN was grown on m-plane sapphire by the hierarchical growth mode. A high density of extended defects due to the lattice mismatch and anisotropic growth rate is identified in the as-grown AlN thin film. The influence of thermal annealing and AlN regrowth on the evolution of stacking faults and dislocations in AlN was thoroughly investigated by high-resolution transmission electron microscopy. Extending defects turned into partial dislocations after high-temperature treatment, by which the stacking faults were buried inside the AlN template, incapable of propagating into the AlN regrowth layer. As a result, the AlN regrowth layer exhibits superior crystalline quality. However, compressive strain is found after high-temperature annealing (HTA), which introduces new defects in the AlN regrowth layer. Strain management is demonstrated to be crucial for the quality control of the AlN layer. Overall, high-temperature annealing and regrowth processes proved to be stable and repeatable techniques in the realization of high-efficiency semipolar UV semiconductor devices.