Phase‐Selective MOCVD of Orthorhombic Ferroelectric Gallium Oxide: Temperature‐Pressure Control of Phase Stability, Crystallinity, and Ferroelectricity for Memristor Applications

ABSTRACT Orthorhombic ferroelectric gallium oxide ε(κ)‐Ga 2 O 3 holds significant promise for non‐volatile functionality in ultra‐wide‐bandgap electronics, yet achieving scalable epitaxy remains a challenge. This study establishes a quantitative materials‐to‐device framework by mapping the temperature‐pressure landscape of metal‐organic chemical vapor deposition, delineating a phase transformation map from amorphous to ε(κ) and β phases. A narrow stability window for phase‐pure ε(κ)‐Ga 2 O 3 is identified between 560–590∘C and 7–23 Torr. Within this regime, phase boundaries are shown to follow an inverse T‐P trade‐off and an Ostwald step rule pathway. A critical kinetic threshold is established: when the growth rate exceeds ∼11‐12 nm/min, the system bypasses the metastable ε(κ) phase in favor of the thermodynamically stable β phase. At the optimized condition of 570°C, the films exhibit a minimum oxygen‐vacancy fraction of 2.1% and peak c‐axis crystalline coherence (rocking‐curve FWHM = 0.56°), which directly amplifies the ferroelectric response. Positive‐Up‐Negative‐Down (PUND) measurements confirm a switchable polarization of 60 nC/cm 2 after excluding leakage contributions. Lateral memristors fabricated from these optimized films deliver an I on /I off ratio of ∼200 and robust synaptic functions, with the spike‐voltage‐dependent plasticity index increasing by 70 percentage points. This work provides a transferable blueprint linking process kinetics to defect chemistry and device‐level performance for ε(κ)‐Ga 2 O 3 ferroelectric memristors.