Quantitative analysis of heterogeneous microstructures in compositionally graded (0001) AlGaN grown by ammonia molecular beam epitaxy
Phys. Rev. Materials 10, 024605 – Published 11 February, 2026
DOI: https://doi.org/10.1103/1kcg-cjns
Abstract
Future high-power, high-frequency transistors may make use of high-Al-content AlGaN due to its large critical electric field and resulting potential for highly scaled devices. Since AlN is the most likely substrate for these devices, there is a significant lattice mismatch between the AlN substrate and lower-Al alloy layers needed for barriers, channels, and contacts. This work demonstrates fully coherent graded AlGaN heterostructures based on AlN templates, which could be implemented into future devices. We show the importance of well-controlled growth conditions, AlGaN layer thicknesses, and composition steps through transmission electron microscopy, atomic force microscopy, and high-resolution x-ray diffraction measurements to guide the epitaxial design of future generations of AlGaN-based transistors. We also emphasize the importance of careful analysis of high-resolution x-ray diffraction data in the context of a heterogeneous microstructure, such as one exhibiting crosshatch, in which there are simultaneously heavily dislocated and coherent crystalline regions in a thin layer.
