First-principles study of oxygen vacancy defects in orthorhombic Hf0.5_{0.5}Zr0.5_{0.5}O2_2/SiO2_2/Si gate stack

The gate defect of the ferroelectric HfO$_2$-based Si field-effect transistor (Si FeFET) plays a dominant role in its reliability issue. The first-principles calculations are an effective method for the atomic-scale understanding of gate defects. However, the first-principles study on the defects of FeFET gate stacks, i.e., metal/orthorhombic-Hf$_{0.5}$Zr$_{0.5}$O$_2$/SiO$_2$/Si structure, has not been reported so far. The key challenge is the construction of metal/orthorhombic-Hf$_{0.5}$Zr$_{0.5}$O$_2$/SiO$_2$/Si gate stack models. Here, we use the Hf$_{0.5}$Zr$_{0.5}$O$_2$(130) high-index crystal face as the orthorhombic ferroelectric layer and construct a robust atomic structure of the orthorhombic-Hf$_{0.5}$Zr$_{0.5}$O$_2$/SiO$_2$/Si gate stack without any gap states. Its high structural stability is ascribed to the insulated interface. The calculated band offsets show that this gate structure is of the type-I band alignment. Furthermore, the formation energies and charge transition levels (CTLs) of defects reveal that the oxygen vacancy defects are more favorable to form compared with other defects such as oxygen interstitial and Hf/Zr vacancy, and their CTLs are mainly localized near the Si conduction band minimum and valence band maximum, in agreement with the reported experimental results. The oxygen vacancy defects are responsible for charge trapping/de-trapping behavior in Si FeFET. This work provides an insight into gate defects and paves the way to carry out the first-principles study of ferroelectric HfO$_2$-based Si FeFET.Comment: 18 pages, 5 figure

COVID-19 vaccine hesitancy and influencing factors among Chinese hospital staff: a cross-sectional study

Abstract We aimed to investigate the willingness of hospital staff to receive the COVID-19 vaccine and explore the associated factors and reasons of vaccine hesitancy among Chinese hospital staff, which were not yet known. A cross-sectional questionnaire survey was conducted online on the vaccine hesitancy of staff in a grade A tertiary general hospital in Beijing from February 22 to 23, 2023. Univariate and multivariate logistic regression were used to assess associations between potential influencing factors and vaccine hesitancy. A total of 3269 valid respondents were included, and the rate of COVID-19 vaccine hesitancy was 32.67%. Multivariate logistic regression showed that women [1.50 (1.22–1.83)], having high-school education level [1.69 (1.04–2.76)], college degree [2.24 (1.35–3.72)] or graduate degree [2.31 (1.33–4.03)], and having underlying disease [1.41 (1.12–1.77)] were associated with a higher rate of COVID-19 vaccine hesitancy. The main reasons for vaccine hesitancy included doubts for the safety and effectiveness of COVID-19 vaccine and worries in adverse reactions. Hospital staff's willingness to vaccinate COVID-19 vaccine is generally high in the study. Hospitals should spread the knowledge of COVID-19 vaccine through multiple channels to improve the cognition of hospital staff and encourage vaccination based on associated factors

Enhanced P-Type GaN Conductivity by Mg Delta Doped AlGaN/GaN Superlattice Structure

A method of combining the AlGaN/GaN superlattices and Mg delta doping was proposed to achieve a high conductivity p-type GaN layer. The experimental results provided the evidence that the novel doping technique achieves superior p-conductivity. The Hall-effect measurement indicated that the hole concentration was increased by 2.06 times while the sheet resistivity was reduced by 48%. The fabricated green-yellow light-emitting diodes using the achieved high conductivity p-type GaN layer showed an 8- and 10-times enhancement of light output power and external quantum efficiency, respectively. The subsequent numerical calculation was conducted by using an Advanced Physical Model of Semiconductor Device to reveal the mechanism of enhanced device performance. This new doping technique offers an attractive solution to the p-type doping problems in wide-bandgap GaN or AlGaN materials

The Study of Reactive Ion Etching of Heavily Doped Polysilicon Based on HBr/O2/He Plasmas for Thermopile Devices

Heavily doped polysilicon layers have been widely used in the fabrication of microelectromechanical systems (MEMS). However, the investigation of high selectivity, anisotropy, and excellent uniformity of heavily doped polysilicon etching is limited. In this work, reactive ion etching of undoped and heavily doped polysilicon-based hydrogen bromide (HBr) plasmas have been compared. The mechanism of etching of heavily doped polysilicon is studied in detail. The final results demonstrate that the anisotropy profile of heavily doped polysilicon can be obtained based on a HBr plasma process. An excellent uniformity of resistance of the thermocouples reached ± 2.11%. This technology provides an effective way for thermopile and other MEMS devices fabrication

Surface chemistry of atmospheric nanoparticles during a haze episode in Beijing by TOF-SIMS

The atmospheric aerosol particles have a potential heavy burden on environment, climate, and human health, which were closely related to the surface physicochemical properties. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) technique is a powerful tool to obtain detailed surface chemical information since it has high surface sensitivity for both elements and molecular ions, and high mass resolution. In this work, size-fractioned aerosol particles in the range of 0.43–10 µm during a severe haze episode in Beijing were analyzed by TOF-SIMS, the variation characteristics of chemical species corresponding to particle size and air pollution level was investigated by the normalization of secondary ion intensities, the possible sources were identified through principal component analysis (PCA), and the influence of meteorological factors and air mass transmission were also investigated. The study results showed that the surface chemical components of PM2.5 were more complicated during haze episode than on clean days. A total of 17 organic and inorganic species were detected, including crustal elements, heavy metals, sulfate, nitrate, siliceous compounds, hydrocarbons, oxygen-containing organics, and nitrogen-containing organics. In general, the particle surface mainly contained crustal elements, hydrocarbons, and carbon-containing inorganics. Organic and secondary ions significantly increased in heavy-polluted days, indicating the aging process of particles. Inorganic compounds had a higher percentage in coarse mode, while organic compounds were higher in accumulation mode. PCA results indicated that urban aerosol during this haze episode mainly came from vehicle emissions (24.7%), coal-fired combustion (22.4%), organic aerosol (19.3%), and dust resuspension (19.6%). The northern air mass could facilitate the dilution of air pollutants with the surface secondary formed components of particles significantly decreased