Impact of Post-Annealing Time Duration on the Structural, Optical and Resistive Switching Properties of RF Sputtered β-Ga₂O₃ Thin Films

Wide bandgap semiconductor gallium oxide (Ga₂O₃) recently began garnering increasing scientific interest owing to its large bandgap of 4.7−4.9 eV. The exceptional thermochemical stability of β-Ga₂O₃ makes it an intriguing material for several applications, including high-power electronic devices, solar-blind UV photodetectors, light-emitting diodes, photocatalysts, transparent conducting oxides, and chemical sensors. This presentation will discuss the impact of post-annealing time on the structural and optical properties of radio-frequency (RF) magnetron-sputtered amorphous Ga₂O₃thin films. 100 nm thick amorphous Ga₂O₃ thin films were deposited on p-type (100) silicon substrates and post-annealed in a tube furnace at 1000 °C under an argon (Ar) atmosphere for different time intervals: 1, 2, and 7 h. Various characterization techniques were used in this investigation, including grazing-incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), and UV-visible- NIR spectrophotometry. GIXRD scans showed that the as-deposited Ga₂O₃ thin films were amorphous. In contrast, all post-annealed thin films were polycrystalline β-Ga₂O₃, exhibiting a monoclinic crystal structure with a C2/m space group and dominant (400) orientation. In addition, the degree of crystallinity and grain size increased upon increasing the annealing time. Cross-sectional TEM of 7 h annealed Ga₂O₃ thin film revealed interplanar distances of 2.93 Å and 2.88 Å, which correspond to the d-spacing of (400) and (002) planes of the β-Ga₂O₃, respectively. Moreover, no solid-state reaction occurred between the underlying Si substrate and the Ga₂O₃ layer. All the Ga₂O₃ thin films exhibit very high transmittance in the UV and visible ranges. The optical bandgap of the as-deposited Ga₂O₃ film is 4.45 eV, which increased after the post-annealing treatment. Finally, we developed a 100 nm Ag/20 nm Ga₂O₃/Si memristive system. The current–voltage (I–V) characteristics of Ag/Ga₂O₃/Si memristor under positive and negative bias voltages have provided valuable information on the ON and OFF states of the device and the corresponding resistive switching mechanism.