Annihilation and Regeneration of Defects in (11(2)over-bar2) Semipolar AlN via High-Temperature Annealing and MOVPE Regrowth

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, (11 (2) over bar2) 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.

Automated summary

This work investigates the growth of semipolar AlN thin films on m-plane sapphire substrates using a hierarchical growth mode, and the effects of thermal annealing and regrowth on the evolution of defects in AlN. The study found that extended defects turned into partial dislocations after high-temperature treatment, leading to improved crystalline quality in the AlN regrowth layer. High-temperature annealing and regrowth processes were demonstrated to be stable and repeatable techniques for high-efficiency semipolar UV semiconductor devices.