Tuning the thickness of exfoliated quasi-two-dimensional β-Ga₂O₃ flakes by plasma etching

We demonstrated the thinning of exfoliated quasi-two-dimensional β-Ga₂O₃ flakes by using a reactive ion etching technique. Mechanical exfoliation of the bulk β-Ga₂O₃ by using an adhesive tape was followed by plasma etching to tune its thickness. Since β-Ga₂O₃ is not a van der Waals material, it is challenging to obtain ultra-thin flakes below a thickness of 100 nm. In this study, an etch rate of approximately 16 nm/min was achieved at a power of 200 W with a flow of 50 sccm of SF₆, and under these conditions, thinning of β-Ga₂O₃ flakes from 300 nm down to ∼60 nm was achieved with smooth morphology. We believe that the reaction between SF₆ and Ga₂O₃ results in oxygen and volatile oxygen fluoride compounds, and non-volatile compounds such as GaF_X that can be removed by ion bombardment. The opto-electrical properties were also characterized by fabricating solar-blind photodetectors using the plasma-thinned β-Ga₂O₃ flakes; these detectors showed fast response and decay with excellent responsivity and selectivity. Our results pave the way for tuning the thickness of two-dimensional materials by using this scalable, industry-compatible dry etching technique.