MOCVD-grown ε(κ)-Ga2O3 with highly preferred orientation for memristor applications

Gallium oxide (Ga 2 O 3 ), a wide-bandgap semiconductor, has attracted attention for advanced electronics due to its high breakdown field and environmental stability. Among its polymorphs, the ε(κ)-phase, characterized by intrinsic spontaneous polarization, offers promise for memristor devices owing to its ferroelectricity. This study reports the heteroepitaxial growth of ε(κ)-Ga 2 O 3 on silicon substrates using a TiN buffer via metal-organic chemical vapor deposition (MOCVD), achieving highly oriented, uniform films across a 2-inch wafer. The crystallization evolves from amorphous to ε(κ)-phase, and finally to β-phase as growth temperature rises from 490 °C to 640 °C. Optimized conditions yield ε(κ)-Ga 2 O 3 with low defect density (XRD FWHM of 0.111°), ∼3 % oxygen vacancies, and near-ideal stoichiometry. Memristor devices fabricated from the as-grown ε(κ)-Ga 2 O 3 exhibit reliable bipolar resistive switching, driven by the spontaneous polarization of the ε(κ)-phase. These devices demonstrate a high R ON /R OFF ratio exceeding 6 × 10 4 , endurance beyond 4 × 10 3 cycles, and switching speeds below 1 μs, underscoring their robust performance and wide memory window. Furthermore, under pulsed voltage stimulation, the devices exhibit key synaptic plasticity functions, including excitatory postsynaptic currents, spike-voltage-dependent plasticity, and spike-number-dependent plasticity. Notably, repeated stimulation enhances the spike-voltage-dependent plasticity index by more than 280-fold, highlighting the device's strong learning capability. These findings underscore the potential of ε(κ)-Ga 2 O 3 as an enabling material for next-generation neuromorphic computing applications.