Tuning the Threshold Voltage of Exfoliated β-Ga2O3 Flake-Based Field-Effect Transistors by Photo-Enhanced H3PO4 Wet Etching

Abstract

Monoclinic β-Ga2O3 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-Ga2O3 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-Ga2O3 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-Ga2O3) thickness achieved by the photo-enhanced H3PO4 etching. Our study paves the way for the implementation of exfoliated β-Ga2O3 nanolayers in nanoelectronics.