Tuning the threshold voltage of exfoliated β-Ga ₂ O ₃ flake-based field-effect transistors by photo-enhanced H ₃ PO ₄ wet etching

Monoclinic β-Ga ₂ O ₃ with an ultra-wide energy bandgap of ∼4.9 eV has facile cleavage planes because of the high anisotropy in the lattice structure. An exfoliated nanolayer flake of β-Ga ₂ O ₃ can be used as an active channel layer in nanoelectronics. However, the mechanical exfoliation method used poses a fundamental issue in that the separated individual layer has a random thickness, which makes it challenging to obtain reproducible device performance. In our study, we demonstrated a photo-enhanced chemical etching technique to control the thickness of exfoliated β-Ga ₂ O ₃ nanolayers, enabling us to adjust the threshold voltage of field-effect transistors (FETs) based on these nanolayers. Thickness-dependent device characteristics (threshold voltage, subthreshold swing, on/off ratio, and field-effect mobility) of the back-gated FETs were investigated as a function of the active channel layer (β-Ga ₂ O ₃ ) thickness achieved by the photo-enhanced H ₃ PO ₄ etching. Our study paves the way for the implementation of exfoliated β-Ga ₂ O ₃ nanolayers in nanoelectronics.