Ion-beam modification of metastable gallium oxide polymorphs

•Structural changes revealed in α + ε(κ)-phase Ga2O3 under Al+ ion irradiation.•Interpretation of new X-ray diffraction peaks after irradiation is twofold.•Either phase transition or strain can be ion-induced in metastable Ga2O3. Structural changes under the action of Al+ irradiation have been investigated by X-ray diffraction for polymorphic Ga2O3 layers grown by halide vapor phase epitaxy on c-plane sapphire and consisting predominantly of α-phase with inclusions of ε(κ)-phase. As a result of irradiation, some new reflections appear, which can be interpreted in two ways – either as a phase transition of the α- and/or ε(κ)-phase to the more stable β-phase, or as a selective radiation-stimulated strain of the ε(κ)-phase, i.e., an increase in the interplanar distance of a family of planes parallel to the surface. The discussed ion-stimulated phenomena have to be taken into account when utilizing ion implantation to modify Ga2O3 properties.