Role of oxygen incorporation in high temperature annealed AlGaN

High-temperature annealing (HTA) is a powerful technique to decrease dislocation density in AlN, which can also be applied on AlGaN. This work investigates the impact of using sapphire and AlN as a material cover during the face-to-face HTA process on Al${}_x$Ga${}_{1-x}$N (0.55 < x < 0.93) properties. Before HTA, the threading dislocation density (TDD) in the AlGaN for all x${}_{Al}$ was about 6.0 × 10${}^9$ cm${}^{-2}$. Meanwhile, after HTA, the sapphire cover led to a further reduction of the TDD at 5.7 × 10${}^9$ cm${}^{-2}$ for the lowest x${}_{Al}$ and 1.4 × 10${}^9$ cm${}^{-2}$ for the highest x${}_{Al}$ in comparison to the AlN cover. In most cases, strain relaxation increased by HTA, especially with the sapphire cover. Furthermore, increased optical absorption in HTA AlGaN can be lessened by the sapphire cover. Such absorption compromises the performance of UV LEDs which usually emit through the substrate. These advantages of sapphire over AlN as the cover in the HTA process are associated with additional oxygen incorporation into the AlGaN, most probably from the surface of the sapphire cover. (© 2023 The Authors. physica status solidi (a) applications and materials science published by Wiley‐VCH GmbH)