A combined approach of atom probe tomography and unsupervised machine learning to understand phase transformation in (AlxGa1−x)2O3

Abstract

In this paper, we investigated the evolution of microstructural chemistry of metal organic chemical vapor deposition grown (010) (AlxGa1−x)2O3 films with varying Al contents, x = 0.10–1.0, using atom probe tomography (APT). At a low Al content (x ≤ 0.25), the films are homogeneous, where layer inhomogeneity appears at a high Al content (x > 0.25). Further increasing the Al content up to x ≥ 0.60 results in a homogeneous (AlxGa1−x)2O3 layer. This change in microstructural features was linked to the phase transformation of (AlxGa1−x)2O3 using a manifold learning approach to capture the governing features hidden in the data dimensionality. Combining APT to unsupervised machine learning enables APT to be an independent material characterization tool to investigate the microstructure, chemical composition, and phase related information.

Probing structural and chemical evolution in (AlxGa1−x)2O3 using atom probe tomography: A review

“…Since wide bandgap semiconductor tips may exhibit poor response to laser pulsing, it is critical to optimize the APT experimental conditions, especially the base specimen temperature and pulse energy beforehand [80]. Experimental parameters including temperature (K), pulse repetition rate (kHz), laser pulse energy (pJ), and evaporation rate (ions per pulse) were optimized to ensure efficient data acquisition from (Al x Ga 1−x ) 2 O 3 tips containing layered structure with varying Al content [28,29,87,88]. The evaporated ions from individual layers are projected and collected in a position-sensitive detector (PSD) that provides the TOF and detection event in 2D positions [89] which is used in the reconstruction of the 3D tip image and data analysis.…”

“…The change in the atomic-level structure and chemical composition of (Al x Ga 1−x ) 2 O 3 at Al content, x > 0.25, results in a degraded crystallinity of the films [28,29,87,88] limiting the solubility of α-Al 2 O 3 in β-Ga 2 O 3 . This crystal degradation was attributed to the phase separations in (Al x Ga 1−x ) 2 O 3 at high Al content [10,26,28,29,30]. Since the phase purity is related to film's homogeneity with well-defined Al/Ga stoichiometry at the atomic level, it is required to study the change in the atomic-level structure and chemistry of (Al x Ga 1−x ) 2 O 3 with Al to conclusively determine the Al solubility limit in this alloy.…”

“…However, significantly degraded device efficiency was reported at high Al content beyond ∼25% [20,25]. This reduced efficiency is due to the crystallinity degradation of (Al x Ga 1−x ) 2 O 3 , arising from the solubility limit of corundum Al 2 O 3 in monoclinic Ga 2 O 3 beyond a certain Al content [10,12,26,27,28,29,30]. The theoretically predicted solubility limit of Al in (Al x Ga 1−x ) 2 O 3 was ∼60% [31,32].…”

Probing structural and chemical evolution in (AlxGa1−x)2O3using atom probe tomography: A review

“…The first step is to divide the sample into multiple sections, and each section will have a respective TOF spectrum as shown in (b-k). Reprinted from Ref [29]. with the permission of AIP Publishing.Invited Feature Paper -Review ▪ Journal of Materials Research ▪ 2020 ▪ www.mrs.org/jmr © The Author(s), 2020, published on behalf of Materials Research Society by Cambridge University Press cambridge./www.cambridge.org/core/terms.…”

“…The flow chart illustrating the algorithm used to perform PCA on the TOF of (Al x Ga 1−x ) 2 O 3 films with x = 0.1-1.0. Reprinted from Ref [29]. with the permission of AIP Publishing.…”