Use of mist chemical vapor deposition to impart ferroelectric properties to ε-Ga2O3 thin films on SnO2/c-sapphire substrates

ε-Ga2O3 has a polar crystal structure with non-inversion-symmetry along the direction of the c-axis. In a previous study, the ferroelectric hysteresis loop of ε-Ga2O3 was successfully measured using a planar-plate capacitor comprising a thick ε-Ga2O3 layer (3 μm). Herein, we aim to enhance the ferroelectric properties of ε-Ga2O3 to allow ferroelectric measurements to be conducted with a lower maximum applied voltage and a higher measurement frequency as compared with previous studies. We successfully observed ferroelectric hysteresis loops of orthorhombic ε-Ga2O3 thin (250 nm) films grown on SnO2 conductive layers on c-sapphire substrates. Moreover, the smooth-surface morphology and improved crystal quality induced ferroelectric properties in the ε-Ga2O3 thin films grown at 750 °C. This material was used to facilitate ferroelectric measurements at a relatively high frequency of 1 kHz with a maximum applied electric field of 0.38 MV/cm and a small remnant polarization (2Pr = 7.6 nC/cm2) at room temperature.