Ex Situ and In Situ Thermal Evolution and Crystallization of Amorphous (In,Ga) 2 O 3

The present study investigates the structural evolution of amorphous (In,Ga)2O3 thin films grown by pulsed laser deposition and thermal annealing under vacuum (ex situ) and in situ transmission electron microscopy (TEM). Ex situ annealing results showed that the crystallization starts close to the substrate interface at 500 °C with randomly oriented nanocrystals, nanovoids, and on top of that, columnar grains of cubic c-(In,Ga)2O3. For the in situ TEM studies, we observed the formation of a heterogeneous polycrystalline mixture of elemental indium (In), monoclinic β-Ga2O3, and a minor contribution of c-In2O3 when annealed at 400 °C. Further annealing at 700 °C led to gradual evaporation of indium, resulting in a β-Ga2O3-dominated sample with nanovoids. These findings provide insights into phase stability, evolution, and elemental redistribution, which are critical for optimizing (In,Ga)2O3 thin films for optoelectronic applications.