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Designing high-performance β-Ga2O3/4H-SiC heterojunctions has been widely investigated in recent years due to their unique applications in photodetectors. Due to the low defect formation energy of oxygen vacancies, β-Ga2O3-based heterojunction photodetectors inevitably produce defects internally upon irradiaion accompanied by performance degradation, yet the underlying physics still remains elusive. Herein, we focus on investigating the influence of oxygen vacancy defects on electronic, optical and carrier transport properties of β-Ga2O3/4H-SiC heterojunctions to understand such degradation mechanisms using first-principles calculations. Our findings indicate that the irradiation-induced oxygen vacancies can significantly reduce the space charge region width of the heterojunction but slightly affect the electrostatic potential. When oxygen vacancies appear at the heterojunction boundary (β-Ga2O3 side), the bandgaps of both β-Ga2O3 and 4H-SiC decrease simultaneously. The interface states emerge when oxygen vacancies occur at the interface but do not affect the bandgaps. In addition, the oxygen vacancies could increase the optical absorption in the visible and ultraviolet bands, leading to more electron–hole pairs being quickly separated through the built-in electric field. Our calculations reveal the oxygen vacancy influence on the β-Ga2O3/4H-SiC heterojunction, which is helpful for analyzing photodetector failures and improving their performances. [ABSTRACT FROM AUTHOR]

β-Ga2O3 with an ultra-wide bandgap demonstrates great promise in applications of space missions as power electronics and solar-blind photodetector. Unraveling the radiation damage effects on its material properties is of crucial importance, especially for improving the radiation tolerance of Ga2O3-based devices. Herein, we evaluate the formation energy of gallium and oxygen vacancy defects and comprehensively investigate their influence on the electronic and optical properties of β-Ga2O3 using first-principles calculations. Ga vacancies act as deep acceptors and produce p-type defects in β-Ga2O3, while the defective Ga2O3 with O vacancies exhibits the n-type characteristics. A semimetal characteristic is observed in the defective Ga2O3 with Ga vacancies, and an apparent optical absorption peak in the infrared spectral range emerges. Moreover, the self-compensation effect emerges when β-Ga2O3 contains both Ga vacancies and O vacancies, leading to the reduced absorption peak. The doping effect on the defect formation energy of β-Ga2O3 is also investigated, and Ga vacancies are found to be easily formed in the case of In doped β-Ga2O3 (InGa2O3) compared to the undoped β-Ga2O3, while O vacancies are much harder to form. This work provides insights into how gallium and oxygen vacancy defects alter electronic and optical properties of β-Ga2O3, seeking to strengthen its radiation tolerance. [ABSTRACT FROM AUTHOR]

The Environmental Trace Gases Monitoring Instrument 2 (EMI-2), a second-generation Chinese hyperspectral satellite-based spectrometer, was launched on 7 September 2021. The total ozone column (TOC) product, which is one of the most important elements of the EMI-2 mission, is required for monitoring the Antarctic ozone hole and regional tropospheric ozone pollution. The first EMI-2 TOC results using the differential optical absorption spectroscopy (DOAS) method are presented in this study. Significant improvements, such as the fitting interval, reference spectrum, and iterative air mass factor (AMF) calculation scheme, were implemented in the EMI-2 TOC retrieval in comparison with the EMI DOAS TOC algorithm, thus generating more accurate reads. The monthly average EMI-2 DOAS TOCs in November 2021 were compared with the TROPOspheric Monitoring Instrument (TROPOMI) TOCs, and the results showed a good correlation (R = 0.99). The EMI-2 TOCs showed similar global spatial distributions to those of TROPOMI, with an overall mean relative bias and mean standard deviation of 0.16% and 2.38%, respectively. However, large differences (up to 7%) appeared in some polar areas near the coastline, which were mainly caused by different surface albedo algorithms. Furthermore, ground-based measurements from 20 stations across different latitudes derived from the World Ozone and Ultraviolet Radiation Data Center dataset were used to assess the accuracy of the EMI-2 DOAS TOCs, and they had a mean relative bias and mean standard deviation of 0.70% and 3.65%, respectively. These results indicate that the EMI-2 DOAS TOC algorithm can yield reliable global TOCs and monitor daily Antarctic TOCs for assessing the healing of ozone holes.