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Power devices rely on ideal edge termination to suppress the electric field crowding and avoid premature breakdown before the material's critical field is reached. In this work, a hybrid electric field management configuration, featuring the combination of beveled-mesa (BM) termination and high-k oxide BaTiO3 field plate (FP), was implemented in Ga2O3 Schottky barrier diodes (SBDs). This BMFP-SBD realizes a breakdown voltage (BV) of 1.7 kV with extremely low reverse leakage current, outperforming the BM terminated SBD with BV of 0.64 kV and bare SBD with BV of 0.22 kV. Based on the temperature-dependent reverse characteristics, the dominant leakage mechanism transforms from Poole–Frenkel (P–F) emission in BM-SBD to variable-range-hopping (VRH) in BMFP-SBD at high bias. In particular, under switching conditions of di/dt up to 420 A/μs, the BMFP-SBD exhibits superior dynamic switching characteristics with a short reverse recovery time of 10.1 ns, which are comparable with those in advanced commercial SiC SBDs. These findings underscore the potential of Ga2O3 SBD enabled by BM and high-k FP edge termination for high-speed and high-voltage power electronics applications. [ABSTRACT FROM AUTHOR]

Impacts of spatial charge inhomogeneities on carrier transport fluctuations and premature breakdown were investigated in Schottky ampere-class Ga2O3 power diodes. Three prominent electron traps were detected in Ga2O3 epilayers by a combination of the depth-resolved capacitance spectroscopy profiling and gradual dry etching. The near-surface trap occurring at 1.06 eV below the conduction band minimum (EC), named E3, was found to be confined within a 180 nm surface region of the Ga2O3 epilayers. Two bulk traps at EC − 0.75 eV (E2*) and at EC − 0.82 eV (E2) were identified and interconnected with the VGa- and FeGa-type defects, respectively. In the framework of the impact ionization model, employing the experimental trap parameters, the TCAD simulated breakdown characteristics matched the experimental breakdown properties well, consistently with inverse proportionality to the total trap densities. In particular, the shallowest distributed E3 trap with the deepest level is responsible for higher leakage and premature breakdown. In contrast, Ga2O3 Schottky diodes without E3 trap exhibit enhanced breakdown voltages, and the leakage mechanism evolves from variable range hopping at medium reverse voltages, to the space-charge-limited conduction at high reverse biases. This work bridges the fundamental gap between spatial charge inhomogeneities and diode breakdown features, paving the way for more reliable defect engineering in high-performance Ga2O3 power devices. [ABSTRACT FROM AUTHOR]

We report an alignment-free gallium oxide (Ga2O3) heterojunction barrier Schottky (HJBS) power diode, which utilizes the self-assembled Ni nanostructures as in situ masks for the trench etching of Ga2O3 and the subsequent selective-area filling of p-type NiO. By increasing the trench depth to 200 nm, the relevant HJBS diode exhibits improved reverse blocking capabilities including the reduced leakage current density of 10−8 A/cm2 (at a reverse bias of 100 V) and the enhanced breakdown voltage of 748 V, while maintaining the forward biasing characteristics similar to the Schottky barrier diode (SBD). The variation of turn-on voltage and the reverse breakdown features indicate the conversion of the HJBS diodes characteristics from Ni/Ga2O3 SBD to the NiO/Ga2O3 p-n heterojunction diode. The electrical field simulations and experimental facts imply that the remarkable lateral pinch-off effect in the 200-nm trenched diodes shields the electric field in the depletion region underneath the Ni/Ga2O3 Schottky contact. This work provides a straightforward strategy to simplify the fabrication process of Ga2O3-based HJBS diodes with both promising forward and reverse performances. [ABSTRACT FROM AUTHOR]

In order to study the electric-field-assisted generation of mobile holes, a capacitance-voltage method is applied to asymmetric capacitancelike devices. The concentration of mobile holes generated from charge-transfer complexes at the CuPc/MoO3 interface was studied both theoretically and experimentally. Furthermore, the efficiency of charge generation at various electric fields was also calculated. The capacitance of the device with only a 0.2 nm MoO3 layer first increased and then decreased during bias sweeping from 0 V to −30 V. The capacitance variation is in good agreement with theoretical calculation, which in turn strongly confirms the existence of electric-field-assisted generation mechanism of the mobile holes. [ABSTRACT FROM AUTHOR]

In this Letter, the trap inhomogeneity within β-Ga2O3 is correlated with the conversion of Shockley–Read–Hall (SRH) recombination in NiO/β-Ga2O3 p+–n heterojunction diodes. For the virgin epi-wafer, both near-surface traps E2 (EC-0.82 eV) and E3 (EC-1.11 eV) and bulk E2* traps (EC-0.76 eV) are identified by a transient capacitance analysis, and the corresponding forward current–voltage characteristics of diodes are well fitted in the framework of field-dependent SRH recombination. The SRH recombination rates for E2, E3, and E2* traps are determined to be 1.3 × 107, 8.6 × 108, and 2.4 × 108 s−1, respectively. In this circumstance, carrier transport under forward bias is governed by trap-assisted tunneling through E3 traps with high recombination rates, and the hysteresis is pronounced. With the removal of the defective surface layer, E2 and E3 traps are almost completely eliminated, together with the reduced density of E2* traps to 5.6 × 1014 cm−3. The resultant diode performs an improved rectification ratio of >1011 at ±3 V and an enhanced reverse breakdown voltage of 1692 V. The elimination of near-surface traps leads to the conversion of carrier transport into the conventional SRH recombination, accompanied by the negligible forward hysteresis characteristics. The established fundamental correlation of carrier transport and traps within Ga2O3 is beneficial to develop a high-performance power rectifier toward practical applications. [ABSTRACT FROM AUTHOR]

In this Letter, we demonstrate a large-area (1-mm2) beveled-mesa p-NiO/β-Ga2O3 bipolar heterojunction diode (HJD) with a high Baliga's figure of merit of 1.84 (2.87) GW/cm2 from DC (pulsed) measurements. Benefiting from the suppression of electric field crowing at the designed mesa edge and bipolar current conductivity modulation, the resultant device exhibits advantageous characteristics, including a low subthreshold slope of 65 mV/decade, a low DC (pulsed) differential specific on-resistance of 2.26 (1.45) mΩ cm2, a high current density of 2 kA/cm2, and a high breakdown voltage of 2.04 kV. In particular, the Ga2O3 HJD exhibits an 800 V/10 A extreme switching capability with 16.4-ns reverse recovery characteristics, as well as high operation stability at a high temperature of 200 °C. This work, thus, makes a significant step toward reaching the promise of a high figure-of-merit in β-Ga2O3 power devices. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated the self-powered solar-blind photodetector based on a polyaniline/α-Ga2O3 hybrid heterojunction. The resultant device exhibited distinct self-power characteristics with a peak photoresponsivity (R) of 8.2 mA/W, a UVC (UV light of wavelength range at 200–280 nm)/UVA (UV light of wavelength range at 320–400 nm) rejection ratio (R220 nm/R400 nm) of 2.97 × 104, and a response decay time (τdec) of 176 μs at zero bias. With an elevated bias to 5 V, the dark current remained in an ultralow level of 0.21 pA, while the rejection ratio and τdec were improved to be 7.13 × 104 and 153 μs, respectively, together with the corresponding external quantum efficiency of 38.4% and a detectivity of 6.63 × 1013 Jones. Thanks to the dual functions of bandpass transmission in the deep-ultraviolet spectral region and the hole spreading transport of the polyaniline layer, the responsivity to the visible light is suppressed with the negligible internal photoemission effect, thus leading to the improved rejection ratio. Furthermore, weak interface interactions in such polyaniline/α-Ga2O3 organic–inorganic hybrid systems avoid the introduction of interfacial trapping centers by lattice mismatch and the stabilization of negatively charged anions (O2−) by (−NH2)-+species in polyaniline deactivate oxygen vacancies at the α-Ga2O3 surface, both of which lead to the negligible persistent photoconductivity effect. As a result, in the aid of the interfacial built-in field, the constructed hybrid heterojunction exhibited a self-powered detecting characteristic and a fast response speed. These findings verify the feasibility of delivering high performance photodetectors by implementing the inorganic/organic hybrid bipolar device design to overcome the difficulty in p-type Ga2O3. [ABSTRACT FROM AUTHOR]

The time invariant behaviors of topological insulators are expected to be changed with magnetic doping, which motivate the present study. Here, we show that for Bi2-xCrxSe3 (0.01 ≤ x ≤ 0.3) thin films grown on Si, the non-trivial topological surface state is weakened by the Cr dopants. The band gap of surface is opened and monotonically increased with Cr concentration up to ∼100 meV at 10 K. Meanwhile, the semiconducting behavior is well-maintained in the bulk owing to the reduction of background doping by means of a modified growth strategy and an in situ passivation method. Besides, we also observe the existence of unconventional ferromagnetic ordering below 35 K, for which the Curie-Weiss Law and conventional/modified Arrott equations do not apply. These observations may further help us investigate extraordinary magneto-electric effect in topological insulators, and the result will also pave the way for realizing the quantized anomalous Hall effect. [ABSTRACT FROM AUTHOR]

Carbon isotope composition of the tissue of several mollusc species gathered from the Huaxi river, in China, a typical karst river, was analysed to determine their potential food sources. The results showed that δ13Ctissues values of gastropod species Cipangopaludina chinensis are about 3%o heavier than the values of bivalve species Corbicula fluminea and Anodonta woodiana, which indicates the different food and nutrition sources between species. According to the δ13C values of mollusc's tissues and the potential food, bivalve species C. fluminea and A. woodiana mainly assimilate phytoplankton and terrestrial plant detritus as food, while gastropod species C. chinensis also utilize sediment organic matter as a food source excluding the phytoplankton and terrestrial plant detritus. Moreover, the preferential food selection behavior and varied metabolic intensity between different ages and individuals may lead to some variation of δ13Ctissues values of C. fluminea. This study will be helpful in defining the role of molluscs in the energy flow of the karst river ecosystem, and to protect and manage those molluscs' resources. [ABSTRACT FROM AUTHOR]

Miyun reservoir, the only surface water source for Beijing city, has experienced water supply decline in recent decades. Previous studies suggest that both land use change and climate contributes the changes of water supply in this critical watershed. However, the specific causes of the decline in Miyun reservoir are debatable in a non-stationary climate in the past four decades. The central objective of this study was to quantify the separate and collective contributions of land use change and climate variability to the decreasing inflow into Miyun reservoir during 1961-2008. Different from previous studies, this work objectively identified breakpoints by analyzing the long-term historical hydrometeorology and land cover records. To effectively study the different impacts of the climate variation and land cover change during different sub-periods, annual water balance model (AWB), climate elasticity model (CEM), and rainfall-runoff model (RRM) were employed to conduct attribution analysis synthetically. We found a significant decrease in annual streamflow (p < 0.01), a significant positive trend in annual potential evapotranspiration (p < 0.01), and an insignificant negative trend in annual precipitation (p> 0.1) during 1961-2008. Combined with historical records, we identified two breakpoints as in 1983 and 1999 for the period 1961-2008 by the sequential Mann-Kendall Test and Double Mass Curve. Climate variability alone did not explain the decrease in inflow to Miyun reservoir. Reduction of water yield was closely related to increase in evapotranspiration rates due to the expansion of forestlands and reduction in cropland and grassland, and was likely exacerbated by increased water consumption for domestic and industrial uses in the basin. Our study found that the contribution to the observed streamflow decline from land use change fell from 64-92% during 19841999 to 36-58% during 2000-2008, whereas the contribution from climate variation climbed from 8-36% during the 1984-1999 to 42-64% during 2000-2008. Model uncertainty analysis further demonstrated that climate warming played a dominant role in streamflow reduction in the 2000s. We conclude that future climate change and variability will further challenge the goal of water supply of Miyun reservoir to meet water demand. A comprehensive watershed management strategy needs to consider the climate variations besides vegetation management. [ABSTRACT FROM AUTHOR]