The effects of post-deposition oxygen annealing temperature on the physical, chemical, and optical properties of gallium oxide (Ga2O3) films were systematically studied in this work. First, Ga2O3 films were deposited on Si (100) substrates by atomic layer deposition (ALD) and then annealed at 500 to 900 ℃ , respectively. Several standard surface analysis methods were used to characterize the Ga2O3 films before and after annealing. X-ray diffraction (XRD) patterns illustrated that the as-deposited (as-dep) amorphous film transitioned to β-phase after annealing at temperatures greater than 600 ℃. Atomic force microscopy (AFM) images showed that the grain size and roughness of the films significantly increased when annealed above 700 ℃ . The effects of the annealing process on optical properties were performed using photoluminescence spectroscopy (PL) and spectroscopic ellipsometry (SE). Moreover, X-ray spectroscopy (XPS) was utilized to extract the oxygen vacancy (VO ) concentration, bandgap, and the energy band alignment of Ga2O3 . With increasing annealing temperature, it was found that the atomic ratio of O/Ga increased while VO decreased monotonically from 47.4% to 27.0%. Density functional theory (DFT) simulation further accounted for energy band shifts resulting from the variation of VO. This study provides a means to achieve high-quality β -Ga2O3 films, highly significant for applications of β-Ga2O3-based ultraviolet photodetectors and other relevant devices.
Due to their high wavelength selectivity and strong anti-interference capability, solar-blind UV photodetectors hold broad and important application prospects in fields like flame detection, missile warnings, and secure communication.
The reliability issues in silicon carbide (SiC)-based devices with gate dielectric formed through heat oxidation are significant factors limiting their application in power devices. Aluminum oxide (Al2O3) was chosen as a high-k material to form the gate oxide layer on top of a SiC substrate. Atomic layer deposition (ALD) was used to fabricate an Al2O3/4H-SiC heterostructure, and the quality of the ALD Al2O3 layer was examined by XPS and electrical experiments. The XPS analysis suggests that the created heterojunction is a type-I heterojunction with ΔEC = 1.89 eV and ΔEV = 1.83 eV. Metal-insulated semiconductor structures with upper and lower Al electrodes were prepared for investigating leakage current and breakdown voltage characteristics. The leakage current density and breakdown electric field of an MOS capacitor structure with an Al2O3/4H-SiC heterojunction are ∼10−10 A/cm2 and 9.3 MV/cm, respectively. The interfacial defect density (Dit) near the conduction band of the MOS capacitive structure with the SiC substrate is 1.44 × 1012 eV−1 cm−2, while the interface charge (Neff) of the oxide layer of this sample can also be controlled at a level of 1011 cm−2. The Al2O3/SiC structure fabricated in this work exhibits superior electrical performance compared to the heterostructure based on the Si substrate and other relevant heterostructures documented in previous studies.
In this paper, high-quality β-Ga2O3 films were grown on silicon substrates by plasma-enhanced atomic layer deposition (PEALD). Effects of annealing temperature on β-Ga2O3 thin films were studied. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray reflection (XRR), and ultraviolet (UV) emission spectroscopy were used to systematically characterize Ga2O3 thin films. AFM test results showed that as annealing temperature increased from 500 to 900 °C, the roughness of film increased from 0.542 to 1.58 nm. XPS test results showed that the concentration of oxygen vacancies in annealed films was significantly reduced. After annealing, the energy band of the film increased from 4.73 to 5.01 eV, and the valence band maximum (VBM) increased from 2.58 to 2.67 eV, indicating that the annealing treatment under a nitrogen atmosphere can improve the quality of films. Results demonstrate that high-quality Ga2O3 films can be obtained by the annealing process after atomic layer deposition (ALD). The proposed method can realize an ideal stoichiometric ratio of the Ga2O3 thin film as well as precise control of its optical, electrical, and microstructural properties. This work lays the foundation for future application of Ga2O3 materials in photoelectric detection, power devices, transparent electronics, and other fields.
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