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High-quality (100)-oriented β-Ga 2 O 3 films were successfully grown on (110) TiO 2 substrates by metalorganic chemical vapor deposition (MOCVD) for the first time. Crystal structure, chemical composition, and surface morphology of the epitaxial β-Ga 2 O 3 films were systematically investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscope (AFM). The epitaxial relationship between the β-Ga 2 O 3 film and the TiO 2 substrate was identified as β-Ga 2 O 3 (100)//TiO 2 (110) with β-Ga 2 O 3 [001]//TiO 2 [ 1 1 ‾ 0 ] and β-Ga 2 O 3 [010]//TiO 2 [001]. These material characterizations confirmed that the β-Ga 2 O 3 film grown at 950 °C exhibited the highest crystalline quality and the smoothest surface. Furthermore, these β-Ga 2 O 3 films were then used to fabricate solar-blind photodetectors (PDs) based on a metal-semiconductor-metal (MSM) structure. Due to the β-Ga 2 O 3 film's best material and surface morphology grown at 950 °C, the β-Ga 2 O 3 PDs showed the best performance with a large photocurrent of 85.3 μA, a responsivity of 2.56 A W−1, and a detectivity of 5 × 1011 Jones. This work explores a new TiO 2 substrate for the heterogeneous epitaxy of β-Ga 2 O 3 films, and opens the door for the development of β-Ga 2 O 3 photonics and electronics on cost-effective mass-producible substrates. • High quality β-Ga 2 O 3 films were epitaxially grown by MOCVD on (110) TiO 2 substrates for the first time. • The epitaxial relationships between the β-Ga 2 O 3 film and the TiO 2 substrate were determined: β-Ga 2 O 3 [001]//TiO 2 [ 1 1 ‾ 0 ] and β-Ga 2 O 3 [010]//TiO 2 [001]. • The effect of the temperature on the surface morphology of β-Ga 2 O 3 film was analyzed. • β-Ga 2 O 3 PDs with MSM structure have been fabricated and excellent optical performance were obtained. [ABSTRACT FROM AUTHOR]

β-Ga 2 O 3 thin films were heteroepitaxially grown on c -plane sapphire substrates with different off-axis angles toward <1 1 ‾ 00> direction by metalorganic chemical vapor deposition (MOCVD), where the crystal quality of the films and the deep-ultraviolet photodetectors (PDs) fabricated on these films were characterized. The effect of sapphire substrates with different off-axis angles on the β-Ga 2 O 3 thin films and the optical performance of β-Ga 2 O 3 PDs are investigated for the first time. (2 ‾ 01)-oriented β-Ga 2 O 3 thin films were grown on sapphire substrates with off-axis angles of 0°, 1.5°, 4°, and 6°. The full width at half maxima (FWHM) of rocking curves decreased significantly with the increase of off-axis angles. The β-Ga 2 O 3 thin films grown on the 6° off-axis angle substrate showed a FWHM of 0.55°, indicating excellent crystal quality. Substrate off-axis angles play a critical role in the nucleation process in the growth of β-Ga 2 O 3 thin films. The step edge on the off-axis substrates serves as the preferential incorporation sites for Ga adatoms. The step terrace width is controlled by the off-axis angle and influences the growth modes depending on the relative magnitude of the step terrace width compared with the Ga adatom diffusion length. In addition, β-Ga 2 O 3 photodetectors with a metal-semiconductor-metal (MSM) structure have been fabricated using these β-Ga 2 O 3 thin films. The β-Ga 2 O 3 PDs fabricated on 6° off-axis sapphire substrate showed excellent optical performance with a large photocurrent of 61 μA, an outstanding photo/dark current ratio of 2.3 × 103, and peak responsivity of 74.6 mA/W. These results can provide important guidance on heterogeneous epitaxy of β-Ga 2 O 3 thin films and photodetectors on cost-effective mass-producible sapphire substrates by MOCVD. [ABSTRACT FROM AUTHOR]

(002)-oriented ε -Ga 2 O 3 thin films were heteroepitaxially grown on p -Si (111) substrates by metalorganic chemical vapor deposition (MOCVD). The introduction of Al 2 O 3 buffer layer significantly improved the crystallinity and surface morphology of the ε -Ga 2 O 3 films. Quasi-vertical deep ultraviolet photodetectors (UV-PDs) were fabricated and characterized based on ε -Ga 2 O 3 films grown with and without the Al 2 O 3 buffer layer. Compared with the n -Ga 2 O 3 / p -Si device, the n -Ga 2 O 3 /Al 2 O 3 / p -Si UV-PDs showed enhanced device performance under 254 nm illumination, including an ultralow dark current of 99.4 pA, a photo-to-dark current ratio of 104, a high ultraviolet responsivity of 8.1 A/W at −10 V, and a fast photo response with rise/decay time of 0.89 s/0.29 s. The improved device performance can be ascribed to the energy band engineering of n -Ga 2 O 3 /Al 2 O 3 / p -Si heterojunction. The Al 2 O 3 layer works not only as a buffer layer but also as an electron-blocking layer, which allows holes to cross the heterojunction under the reverse bias. This work shows a promising method to develop high-performance ε -Ga 2 O 3 UV-PDs on cost-effective Si substrates. • Al 2 O 3 buffer layer was used to relieve the larger lattice mismatch between Si and Ga 2 O 3 and utilized to grown high-quality ε -Ga 2 O 3 films on p -Si (111) substrate by MOCVD. • The role of Al 2 O 3 buffer layer in the band of n -Ga 2 O 3 /Al 2 O 3 / p -Si heterojunction is analyzed. • ε -Ga 2 O 3 photodetectors with a PIN structure have been fabricated and shows better optical performance compared with device of PN structure. [ABSTRACT FROM AUTHOR]

ε-Ga2O3 (002) thin films were successfully grown on Si (100) substrate by metalorganic chemical vapor deposition (MOCVD). The crystal structure, chemical composition, and surface morphology of ε-Ga2O3 (002) thin films were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The lattice mismatch between Si and ε-Ga2O3 was effectively reduced by inserting Molybdenum (Mo) buffer layer. Quasi-vertical ε-Ga2O3 Schottky barrier diode (SBD) solar-blind photodetectors grown on Si (100) substrate with the Mo buffer layer were fabricated and characterized. The device has a photo-to-dark current ratio (PDCR) of 1.57 × 103, a responsivity (R) of 243.14 A·W-1, a detectivity (D*) of 1.83 × 1017 Jones (cm·Hz1/2 W−1), and an excellent response time due to improved crystal quality and the vertical device structure. This work provides an important reference for the heteroepitaxial growth of ε-Ga2O3 on Si, which is beneficial to the development of low-cost, high-performance ε-Ga2O3 optoelectronic and power electronic devices. • This work proves that the crystal quality of Mo films increases with the increase of annealing temperature. • High quality gallium oxide crystal thin films have been successfully epitaxial grown on Si. • The epitaxial relationship between Mo and ε-Ga 2 O 3 was demonstrated to be consistent with ε-Ga 2 O 3 (002)//Mo (110) and ε-Ga 2 O 3 (101)//Mo (211). • ε-Ga 2 O 3 photodetectors with a Schottky barrier diode (SBD) structure have been fabricated and excellent optical performance were obtained. [ABSTRACT FROM AUTHOR]