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α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3. [ABSTRACT FROM AUTHOR]

α-Al2O3 is renowned for its extensive bandgap and diverse applications in electronic and optoelectronic devices. Employing density-functional theory-based methods, this study investigates the feasibility of chalcogen doping (S, Se, Te) in α-Al2O3. Standard modeling tools are utilized to construct α-Al2O3 supercells, focusing on the calculations of individual chalcogen-related and native point defects resulting from single-atom doping. Our analysis systematically explores the formation energies and transition levels associated with chalcogen (S, Se, Te) doping in oxygen (or aluminum) sites in Al-rich (or O-rich) limits. We observe a trend where increasing atomic number (from S to Te) correlates with a higher difficulty in forming anion-doped α-Al2O3, but a lower barrier to cationic doping. The results indicate a preferential substitution of chalcogen atoms for aluminum in O-rich environments. Specifically, in varying oxygen conditions, the dominant defect types, their prevalence, and defect formation energies in α-Al2O3 are significantly altered following chalcogen doping, offering new insights into defect processes in α-Al2O3. [ABSTRACT FROM AUTHOR]

This study is the first to explore the effect of selenium doping on the electronic properties of β-Ga2O3 through first-principles calculations. Selenium doping in β-Ga2O3 is a significant choice, as it has the potential to improve the material's electronic properties. Previous work on β-Ga2O3 has focused primarily on other dopants, and the effect of selenium doping is not well understood. Therefore, this study fills an important gap in the current understanding of β-Ga2O3 doping. Selenium doping in β-Ga2O3 was studied by first-principles calculations with a hybrid functional, as this functional can offer a more accurate description of electronic properties, resulting in accurate electronic bandgap and defect level calculations. Our first-principles calculations reveal that selenium can be incorporated on both Ga and O sites under specific conditions. Specifically, under O-rich conditions, selenium atoms are more likely to substitute the Ga sites, whereas under Ga-rich conditions, they are more likely to substitute the O sites. With the formation energy analysis, our findings indicate that selenium doping on Ga sites can lead to n-type conductivity, with it acting as shallow donor. On the other hand, Se dopants at the O sites exhibit deep donor characteristics, rendering it ineffective in regulating the conductivity of β-Ga2O3 materials. Our findings suggest that Se can be used as a dopant to tune the β-Ga2O3 conductivity for electronic and photonic applications, provided that the atomic substitution on Ga sites can be effectively controlled. Our results will provide valuable theoretical insights for the refined use of selenium dopants in β-Ga2O3, as well as guidance and theoretical support for subsequent researchers in the selection of Ga2O3 dopants. [ABSTRACT FROM AUTHOR]

Density functional theory computations were utilized to quantify the polarization discontinuity of 1.8 μC/cm2 in ε-(B0.0625Ga0.9375)2O3/ε-Ga2O3 heterostructure. The polarization effect was sufficient to generate a two-dimensional electron gas (2DEG) at the heterostructure interface without doping. The creation of 2DEG occurred when the BGaO layer thickness exceeded 17 nm, with its density exhibiting a logarithmic increase as the thickness was augmented. However, the trend plateaued when the thickness surpassed 80 nm with a carrier density of 8.17 × 1012 cm–2. Moreover, guided by Griffith's theory and enthalpy calculations, the epitaxial layer could potentially be pseudomorphically grown up to 968 nm under growth conditions of 1000 K with dilute boron alloying. This design heralds the potential for creating a high electron mobility transistor based on ε-BGaO with an epitaxial layer just nanometers thick, well-suited for high-power and radio frequency applications. [ABSTRACT FROM AUTHOR]

Many multi-story residential buildings have been built in villages to improve the living quality of rural residents in China. Therefore, village morphology has dramatically changed compared to the past. Since northern China continues to suffer from environmental problems, improving village ventilation by optimizing village morphology is essential for creating a good rural environment. In this study, 17 morphology models were categorized based on 383 actual villages in Tianjin. In addition, the ventilation capacity of courtyards and streets and residents' health risks of different morphology cases were analyzed. For the northwest wind direction, the ventilation capacity of the courtyards in the northern part of the village can be improved when there are multi-story residences in the north or west of the village. Accordingly, in the southeast wind direction, multi-story buildings in the south or east of the village can improve the courtyard ventilation in the southern part of the village. In addition, multi-story buildings in the west or east of the village can form ventilation corridors in the northwest or southeast wind direction. The morphologies without multi-story buildings in the west or east of the village were recommended to be applied in the village planning in Tianjin due to good ventilation capacity and low exposure risks. [ABSTRACT FROM AUTHOR]