Defect annihilation mechanism of AlN buffer structures with alternating high and low V/III ratios grown by MOCVD

Abstract

A novel structure was built by alternating high and low V/III ratios to improve the quality of the AlN layer at a lower temperature (1100 °C) as compared with conventional growth temperatures (≥1300 °C). This novel structure was applied to fabricate the stacking structure and superlattice layers. We designed four different AlN epitaxial structures to verify the effect of these new structures on the crystallinity. The dislocation density decreased by about one order of magnitude from 7.8 × 10⁹ cm⁻² to 7.4 × 10⁸ cm⁻² after inserting the superlattice in the middle AlN layer. The full width at half maximum values of AlN (0002) and (10−12) also were improved. Interestingly, we found that the growth mechanism and dislocation behavior were greatly dependent on the inserting sites of the superlattice by transmission electron microscopy. As the superlattice was grown first, the growth of the AlN layer was dominated by an island mode forming a column-like structure with twist boundaries. Most of the threading dislocations were decreased by bending and combining with each other along the grain boundary in the columnar structure. We believed that this novel structure could help achieve the growth of an AlN epilayer with optimal quality at a low temperature under the consideration of prolonging the lifetime of the heating system.