Evolution of AlN Step Bunching Morphology During High-Temperature Annealing

Abstract

Abstract: In this article, an AlN epitaxial layer with a step bunching surface morphology was grown on 0.2° to 1.0° offcut angle c-plane sapphire substrates by metal organic chemical vapor deposition (MOCVD), and the evolution regularity of the surface morphology during high-temperature annealing (HTA) was systematically studied. The underlying physical mechanisms were further uncovered through first-principles calculations. It is revealed that as the annealing temperature gradually increase, thermal etching pits with hexagonal structure characteristics first appear on step edges, and then polygonal pits with regular edges formed on the step terraces. The main reason is that the energy of Al-N pairs decomposed from AlN surface at the step-bunching edges (10.72 eV) is smaller than that of Al-N pairs decomposed from the step terraces (12.12 eV), which leads to the phenomenon that the morphology of step edges will change firstly during HTA. In addition, because the width of the step becomes narrower with the increase of the miscut angle, the pits of the step terraces tend to merge with the pits of the step edges during the expansion process to form a V-shaped edge, resulting in step terraces with large miscut angle hardly appearing pits. This study clarifies the evolution mechanism of step-bunching morphology of AlN grown on sapphire substrates with various offcut angles during high-temperature annealing, and provides theoretical support for the preparation of high-quality AlN templates. This template can be used for AlGaN in-plane composition modulation to obtain high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs).

Key words: AlN, surface morphology, high-temperature anneal, step bunching, miscut substrate, thermal etch

CLC Number:

O78
O793

NIE Zikai, BEN Jianwei, ZHANG Entao, MA Xiaobao, ZHANG Shanli, SHI Zhiming, LYU Shunpeng, JIANG Ke, SUN Xiaojuan, LI Dabing. Evolution of AlN Step Bunching Morphology During High-Temperature Annealing[J]. Journal of Synthetic Crystals, 2023, 52(6): 1016-1024.

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