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.

In this work, the atomic level doping of Sn into Ga₂O₃ films was successfully deposited by using a plasma-enhanced atomic layer deposition method. Here, we systematically studied the changes in the chemical state, microstructure evolution, optical properties, energy band alignment, and electrical properties for various configurations of the Sn-doped Ga₂O₃ films. The results indicated that all the films have high transparency with an average transmittance of above 90% over ultraviolet and visible light wavelengths. X-ray reflectivity and spectroscopic ellipsometry measurement indicated that the Sn doping level affects the density, refractive index, and extinction coefficient. In particular, the chemical microstructure and energy band structure for the Sn-doped Ga₂O₃ films were analyzed and discussed in detail. With an increase in the Sn content, the ratio of Sn–O bonding increases, but by contrast, the proportion of the oxygen vacancies decreases. The reduction in the oxygen vacancy content leads to an increase in the valence band maximum, but the energy bandgap decreases from 4.73 to 4.31 eV. Moreover, with the increase in Sn content, the breakdown mode transformed the hard breakdown into the soft breakdown. The C-V characteristics proved that the Sn-doped Ga₂O₃ films have large permittivity. These studies offer a foundation and a systematical analysis for assisting the design and application of Ga₂O₃ film-based transparent devices.

In this study, silicon nitride (SiN_x) thin films with different oxygen concentration (i.e., SiON film) were precisely deposited by plasma enhanced atomic layer deposition on Si (100) substrates. Thus, the effect of oxygen concentration on film properties is able to be comparatively studied and various valuable results are obtained. In detail, x-ray reflectivity, x-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry are used to systematically characterize the microstructural, optical, and electrical properties of SiON film. The experimental results indicate that the surface roughness increases from 0.13 to 0.2 nm as the oxygen concentration decreases. The refractive index of the SiON film reveals an increase from 1.55 to 1.86 with decreasing oxygen concentration. Accordingly, the band-gap energy of these films determined by oxygen 1s-peak analysis decreases from 6.2 to 4.8 eV. Moreover, the I-V tests demonstrate that the film exhibits lower leakage current and better insulation for higher oxygen concentration in film. These results indicate that oxygen affects microstructural, optical, and electrical properties of the prepared SiN_x film.

Low-noise amplification performance of an enhancement-mode p- GaN gate high electron mobility transistor (HEMT) is thoroughly investigated. Featuring a tungsten (W) gate metal and CMOS-compatible metal contacts to source/drain terminals, the device exhibits a positive threshold voltage of 2.7 V. Low gate leakage current density ( $\text{I}_{\text {G}}{)}$ of 3.8 pA/mm and 16.3 nA/mm are extracted in pinch-off region and on-state region, respectively. The device delivers an input third-order interception point (IIP3) of 15.8 dBm at 2 GHz, together with good immunity of linearity characteristics against frequency change. A minimum noise figure ( $NF_{\text {min}}{)}$ of 0.9 dB with an associated gain ( $\text{G}_{\text {a}}{)}$ of 12.8 dB are achieved at a working frequency of 2 GHz. Furthermore, an examination of the bias and frequency effects on NFmin and $\text{G}_{\text {a}}$ reveals NFmin of 0.65 dB and $\text{G}_{\text {a}}$ of 18.3 dB at 1 GHz. This work paves a solid path for the utilization of ${p}$ -GaN HEMT for low noise amplifier applications.

The total ionizing dose effect of Mg-doped p-GaN gate stack have been investigated in this Letter on the whole gate voltage swing arranging from −1.3 to +1.5V. Additionally, two distinct kinds of mechanisms of trap effects have been extracted, which are response to in turns three phases of mechanism, voltage-controlled, coexist of voltage/current-controlled and current-controlled. It indicates that the fast traps are located at p-GaN/AlGaN interface (ET is about 0.295–0.333 eV), while the slow traps are located at AlGaN/GaN interface (ET is about 0.393–0.485 eV). They both have increasing trap density and broader range under γ-ray radiation. When the applied gate voltage rises to about 1 V, the effects of slow trap states are significantly weakened. However, the fast trap states barely change. Finally, the complete transition into current-controlled mode is observed at 1.5 V. What is more, p-GaN/AlGaN interface traps are further extracted near the gate turn-on voltage under γ-ray irradiation rather than the voltage-controlled mechanism of weak accumulation at the threshold voltage. Under the 600 krad γ-ray irradiation, the holes trap at p-GaN/AlGaN interface is identified with the trap activation energy ET at about 0.28–0.3 eV and trap density of about 4 × 1012 cm−2 eV−1. The increase in trap induces the reduction of gate current. In summary, this work can further our understanding of radiation tolerance and trapping effects of p-GaN gate high-electron mobility transistors for power switches, especially in regard to forward conduction status.

In this Letter, trapping effects of a Schottky lightly Mg-doped p-GaN gate stack for low-power applications have been investigated, and further analysis focusing on AlGaN/GaN interface traps under γ-ray irradiation has been carried out. A negligible shift in the flatband voltage with γ-ray irradiation dose up to 800 krad indicates the superior radiation tolerance of the p-GaN gate structure. The difference between capacitance dispersion at the measurement frequency below and above 500 kHz is observed, which is attributed to trapping effects in different locations with varying gate voltage. Moreover, the frequency-dependent conductance method is put forward to assess the effects of different doses of γ-ray irradiation on the AlGaN/GaN interface traps. Based on that method, aside from the shallow trap states [the trap activation energy (E_T) is about 0.334–0.338 eV] previously found in the traditional normally on high electron mobility transistor (HEMT), another type of deeper trap states at the AlGaN/GaN interface (E_T is about 0.467–0.485 eV) is detected. It is observed that the E_T of shallow trap states distributes at a deeper and broader range as the irradiation dose increases. Additionally, the trap density decreased after 600 krad doses irradiation but increased after 800 krad doses irradiation for both deep and shallow E_T. Transmission electron microscopy and atomic force microscopy are used to demonstrate the smooth AlGaN/GaN interface morphology, which will not be greatly damaged after 800 krad doses of γ-ray irradiation. This work can provide a further understanding of radiation tolerance and trapping effects of p-GaN gate HEMTs for low-voltage applications.