Atomic scale control of the thickness of thin film makes atomic layer deposition highly advantageous in the preparation of high quality super-lattices. However, precisely controlling the film chemical stoichiometry is very challenging. In this study, we deposited SiO_x film with different stoichiometry by plasma enhanced atomic layer deposition. After reviewing various deposition parameters like temperature, precursor pulse time, and gas flow, the silicon dioxides of stoichiometric (SiO₂) and non-stoichiometric (SiO_1.8 and SiO_1.6) were successfully fabricated. X-ray photo-electron spectroscopy was first employed to analyze the element content and chemical bonding energy of these films. Then the morphology, structure, composition, and optical characteristics of SiO_x film were systematically studied through atomic force microscope, transmission electron microscopy, X-ray reflection, and spectroscopic ellipsometry. The experimental results indicate that both the mass density and refractive index of SiO_1.8 and SiO_1.6 are less than SiO₂ film. The energy band-gap is approved by spectroscopic ellipsometry data and X-ray photo-electron spectroscopy O 1s analysis. The results demonstrate that the energy band-gap decreases as the oxygen concentration decreases in SiO_x film. After we obtained the Si-rich silicon oxide film deposition, the SiO_1.6/SiO₂ super-lattices was fabricated and its photoluminescence (PL) property was characterized by PL spectra. The weak PL intensity gives us greater awareness that more research is needed in order to decrease the x of SiO_x film to a larger extent through further optimizing plasma-enhanced atomic layer deposition processes, and hence improve the photoluminescence properties of SiO_x/SiO₂ super-lattices.

We described a highly efficient polarizing beam splitter (PBS) of a deep-etched binary-phase fused-silica grating, where TE- and TM-polarized waves are mainly diffracted in the $-1$st and 0th orders, respectively. To achieve a high extinction ratio and diffraction efficiency, the grating depth and period are optimized by using rigorous coupled-wave analysis, which can be well explained based on the modal method with effective indices of the modes for TE/TM polarization. Holographic recording technology and inductively coupled plasma etching are employed to fabricate the fused-silica PBS grating. Experimental results of diffraction efficiencies approaching 80% for a TE-polarized wave in the $-1$st order and more than 85% for a TM-polarized wave in the 0th order were obtained at a wavelength of $1550\mathrm{nm}$. Because of its compact structure and simple fabrication process, which is suitable for mass reproduction, a deep-etched fused-silica grating as a PBS should be a useful device for practical applications.

Ga₂O₃ has emerged as a promising ultrawide bandgap semiconductor for numerous device applications owing to its excellent material properties. In this paper, we present a comprehensive review on major advances achieved over the past thirty years in the field of Ga₂O₃-based gas sensors. We begin with a brief introduction of the polymorphs and basic electric properties of Ga₂O₃. Next, we provide an overview of the typical preparation methods for the fabrication of Ga₂O₃-sensing material developed so far. Then, we will concentrate our discussion on the state-of-the-art Ga₂O₃-based gas sensor devices and put an emphasis on seven sophisticated strategies to improve their gas-sensing performance in terms of material engineering and device optimization. Finally, we give some concluding remarks and put forward some suggestions, including (i) construction of hybrid structures with two-dimensional materials and organic polymers, (ii) combination with density functional theoretical calculations and machine learning, and (iii) development of optical sensors using the characteristic optical spectra for the future development of novel Ga₂O₃-based gas sensors.

The energy band alignment of AlN/β-Ga₂O₃ heterostructures was investigated by X-ray photoelectron spectroscopy. The valence band offsets were estimated to be −0.09 ± 0.1 eV (type II alignment) for AlN grown by plasma enhanced atomic layer deposition (PEALD) on β-Ga₂O₃ and 0.72 ± 0.1 eV (type I alignment) for AlN prepared by thermal atomic layer deposition (T-ALD) on β-Ga₂O₃, which gives the conduction band offsets of 1.39 ± 0.1 eV for PEALD AlN and 0.58 ± 0.1 eV for T-ALD AlN. The large difference in the band alignment for the AlN/β-Ga₂O₃ heterostructures is dominated by different levels of oxygen incorporation into the AlN films as a result of different deposition techniques. The determination of the band alignment of the AlN/β-Ga₂O₃ heterostructure has significant implications for the design of electronic and optical devices based on AlN/β-Ga₂O₃ heterojunctions.

We present the design and fabrication of a novel dual-function subwavelength fused-silica grating that can be used as a polarization-selective beam splitter. For TM polarization, the grating can be used as a two-port beam splitter at a wavelength of $1550\mathrm{nm}$ with a total diffraction efficiency of 98%. For TE polarization, the grating can function as a high-efficiency grating, and the diffraction efficiency of the -1st order is 95% under Littrow mounting. This dual-function grating design is based on a simplified modal method. By using the rigorous coupled-wave analysis, the optimum grating parameters can be determined. Holographic recording technology and inductively coupled plasma etching are used to manufacture the fused-silica grating. Experimental results are in agreement with the theoretical values.