N. Zainal^a,b, S. Hagedorn^a, N.S. Azmi^a,b, T. Kolbe^a, C. Netzel^a, A. Mogilatenko^a, M. Weyers^a

Published in:

Mater. Sci. Semicond. Process., vol. 200, pp. 109949 (2025).

Abstract:

The high temperature annealing (HTA) process has recently emerged as a promising method to significantly reduce the threading dislocation density (TDD) in AlGaN. However, the process can degrade the AlGaN surface, especially for Si-doped AlGaN layers due to Ga loss during HTA. Particularly, surface pits and protruding nanocolumns are observed after HTA. This study attempts to address this issue by removing a surface part of the Si-doped HTA AlGaN layers via inductively coupled plasma etching. With the optimal layer removal, the low TDD can be maintained. Meanwhile, the in-plane lattice constant, a, is still larger than that of the reference AlN layers. Furthermore, the etching effectively recovers the transparency of the annealed AlGaN layers. Nonetheless, the etching enlarges the nanocolumns formed by the HTA process, causing rougher surfaces. Pits are also still observed. The surface can be smoothened by treating the annealed AlGaN through a series of annealing steps, including the deposition of a thin pseudomorpic AlN layer. The use of the treated HTA-AlGaN:Si layer as a template for the growth of AlGaN based UVB LED heterostructure is demonstrated.

Keywords:

AlGaN; HTA; Ga loss; Inductive couple plasma etching; Hydrogen and ammonia annealing

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