Thermodynamic and Kinetic Effects on the Nucleation and Growth of ε/κ- or β-Ga2O3 by Metal-Organic Vapor Phase Epitaxy

In this paper, we focus on the growth of beta- and epsilon/kappa-Ga2O3 thin films via metal- organic vapor phase epitaxy on c-plane sapphire using water and trimethyl-gallium at temperatures between 610 and 650 degrees C. Using these precursors, the monoclinic beta-phase is usually obtained only at temperatures higher than 700 degrees C. We show her; for the first time, that both beta-and epsilon-Ga2O3 can also be obtained by tuning the growth rate of the film, that is, by controlling the supersaturation of the vapor phase. The experimental findings are discussed in the framework of classical nucleation theory and Ostwald's step rule, showing the interplay of thermodynamic (related to different chemical potentials for the metastable epsilon/kappa phase and the stable beta phase) and kinetic effects (mainly related to different surface energy barriers for nuclei of different crystallographic phases/planes). The experimental conditions that permit the nucleation and growth of the desired Ga2O3 polymorph are identified and thoroughly explained, giving to this work a fundamental as well as a technological relevance.

Automated summary

This paper focuses on growing beta- and epsilon/kappa-Ga2O3 thin films using metal-organic vapor phase epitaxy on c-plane sapphire at temperatures between 610 and 650 degrees C. The study shows that tuning the growth rate of the film can result in obtaining both beta- and epsilon-Ga2O3, with the experimental findings discussed in the framework of classical nucleation theory and Ostwald's step rule to understand the interplay of thermodynamic and kinetic effects. The experimental conditions enabling the nucleation and growth of the desired Ga2O3 polymorph are identified and explained, highlighting the fundamental and technological relevance of this work.