Kinetic study of <b> <i>κ</i> </b> ( <b> <i>ε</i> </b> ) to <b> <i>β</i> </b> phase transformation in Ga2O3 thin films via <i>in situ</i> high-temperature XRD

Abstract

The kinetics of the κ(ε) to β-Ga2O3 phase transformation were investigated in five batches of nominally phase-pure κ(ε)-Ga2O3 thin films heteroepitaxially grown on c-plane sapphire, with film thickness ranging from 700 to 1100 nm, using in situ high-temperature x-ray diffraction. Phase fractions were quantitatively extracted through modified Rietveld refinement that accounts for preferred orientation, and the transformation kinetics were analyzed using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model. The applicability of the JMAK model to thin-film materials was evaluated, and its lower and upper bounds for thin films and bulk materials were established. Based on this analysis, a model specifically suited for thin-film kinetic studies was developed and yielded reproducible and robust results across all five sample batches. The results indicate that the κ(ε) to β phase transformation in ∼700–1100 nm films is best described as a diffusionless transformation comprising local atomic rearrangements with effectively two-dimensional (2D) growth, as evidenced by an Avrami exponent near 2 throughout the transformation interval.