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The lack of p-type doping has impeded the development of vertical gallium oxide (Ga2O3) devices. Current blocking layers (CBL) using implanted deep acceptors has been used to demonstrate vertical devices. This paper presents the first demonstration of in situ Mg-doped beta-Ga2O3 CBLs grown using metalorganic chemical vapor deposition. Device structures were designed with in-situ Mg doped layers with varied targeted Mg doping concentrations, which were calibrated by quantitative secondary ion mass spectroscopy (SIMS). The effectiveness of the CBL is characterized using temperature dependent current-voltage measurements using n-Mg-doped-n structures, providing crucial insight into the underlying mechanisms. To further validate the experimental results, a TCAD simulation is performed and the electrically active effective doping is found to be dependent on the Mg-doping density, offering a new perspective on the optimization of CBL performance. Breakdown measurements show a 3.4 MV/cm field strength. This study represents a significant step forward in the development of Ga2O3-based devices and paves the way for future advancements in this exciting field.

This letter reports a highly scaled 90 nm gate length beta-Ga2O3 T-gate MOSFET with no current collapse and record power gain cut off frequency (fMAX). The epitaxial stack of 60 nm thin channel MOSFET was grown by Molecular Beam Epitaxy (MBE) and highly doped (n++) contact regrowth was carried out by Metal Organic Chemical Vapour Deposition (MOCVD) in the source/drain region. Maximum on current (IDS, MAX) of 160 mA/mm and transconductance (gm) around 36 mS/mm was measured at VDS= 10 V for LSD= 1.5 micrometer channel length. Transconductance is limited by higher channel sheet resistance (Rsheet). We observed no current collapse for both drain and gate lag measurement even at higher VDG,Q quiescent bias points. This is the first report of Ga2O3 FET showing no current collapse without any external passivation. Breakdown voltage around 125 V was reported for LGD= 1.2 micrometer. We extracted 27 GHz current gain cut off frequency (fT) and 100 GHz fMAX for 20 V drain bias. fMAX value mentioned here is the highest for Ga2O3 and the first demonstration of 100 GHz operation. fT. VBR product of 3.375 THz.V has been calculated which is comparable with state-of-art GaN HEMT. This letter suggests that Ga2O3 can be a suitable candidate for X-band application.

Experiments have found that diffusion in metabolically active cells is much faster than in dormant cells, especially for large particles. However, the mechanism of this size-dependent diffusion enhancement in living cells is still unclear. In this work, we approximate the net effect of metabolic processes as a white-noise active force and simulate a model system of bacterial cytoplasm with a highly polydisperse particle size distribution. We find that diffusion enhancement in active cells relative to dormant cells can be more substantial for large particles. Our simulations agree quantitatively with the experimental data of Escherichia coli, suggesting an autocorrelation function of the active force proportional to the cube of particle radius. We demonstrate that such a white-noise active force is equivalent to an active force of about 0.57 pN with random orientation. Our work unveils an emergent simplicity of random processes inside living cells., Comment: 20 pages, 18 figures

The in-situ metalorganic chemical vapor deposition (MOCVD) growth of Al$_2$O$_3$ dielectrics on $β$-Ga$_2$O$_3$ and $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films is investigated as a function of crystal orientations and Al compositions of $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films. The interface and film qualities of Al$_2$O$_3$ dielectrics are evaluated by high resolution X-ray diffraction (HR-XRD) and scanning transmission electron microscopy (HR-STEM) imaging, which indicate the growth of high quality amorphous Al$_2$O$_3$ dielectrics with abrupt interfaces on (010), (100) and (-201) oriented $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films. The surface stoichiometries of Al$_2$O$_3$ deposited on all orientations of $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ are found to be well maintained with a bandgap energy of 6.91 eV as evaluated by high resolution x-ray photoelectron spectroscopy, which is consistent with the atomic layer deposited (ALD) Al$_2$O$_3$ dielectrics. The evolution of band offsets at both in-situ MOCVD and ex-situ ALD deposited Al$_2$O$_3$/$β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ are determined as a function of Al composition, indicating the influence of the deposition method, orientation, and Al composition of $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ films on resulting band alignments. Type II band alignments are determined at the MOCVD grown Al$_2$O$_3$/$β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ interfaces for (010) and (100) orientations, whereas type I band alignments with relatively lower conduction band offsets are observed along (-201) orientation. Results from this work revealed that the in-situ MOCVD deposited high quality Al$_2$O$_3$ dielectrics with sharp interfaces can be considered as a viable alternative of commonly used ex-situ deposited (ALD) Al$_2$O$_3$ for developing high performance $β$-Ga$_2$O$_3$ and $β$-(Al$_x$Ga$_{1-x}$)$_2$O$_3$ based devices.

This letter reports high-performance $\mathrm{\beta} Ga2O3 thin channel MOSFETs with T-gate and degenerately doped source/drain contacts regrown by MOCVD. Gate length scaling (LG= 160-200 nm) leads to a peak drain current (ID,MAX) of 285 mA/mm and peak trans-conductance (gm) of 52 mS/mm at 10 V drain bias with 23.5 Ohm mm on resistance (Ron). A low metal/n+ contact resistance of 0.078 Ohm mm was extracted from TLM measurement. Ron is dominated by interface resistance between channel and regrown layer. A gate-to-drain breakdown voltage of 192 V is measured for LGD = 355 nm resulting in average breakdown field (E_AVG) of 5.4 MV/cm. This E_AVG is the highest reported among all sub-micron gate length lateral FETs. RF measurements on 200 nm Silicon Nitride (Si3N4) passivated device shows a current gain cut off frequency (f_T) of 11 GHz and record power gain cut off frequency (f_MAX) of 48 GHz. The f_T.V_Br product is 2.11 THz.V for 192 V breakdown voltage. The switching figure of merit exceeds that of silicon and is comparable to mature wide-band gap devices.

Additional file 1.

Epitaxial growth of \k{appa}-phase Ga2O3 thin films are investigated on c-plane sapphire, GaN- and AlNon-sapphire, and (100) oriented yttria stabilized zirconia (YSZ) substrates via metalorganic chemical vapor deposition (MOCVD). The structural and surface morphological properties are investigated by comprehensive material characterization. Phase pure \k{appa}-Ga2O3 films are successfully grown on GaN-, AlN-on sapphire, and YSZ substrates through a systematical tuning of the growth parameters including the precursor molar flow rates, chamber pressure and growth temperature, whereas the growth on c-sapphire substrates leads to a mixture of \b{eta}- and \k{appa}polymorphs of Ga2O3 under the investigated growth conditions. The influence of the crystalline structure, surface morphology and roughness of \k{appa}-Ga2O3 films grown on different substrates are investigated as a function of precursor flow rate. High resolution scanning transmission electron microscopy (HR-STEM) imaging of \k{appa}-Ga2O3 films reveals abrupt interfaces between the epitaxial film and the sapphire, GaN and YSZ substrates. The growth of single crystal orthorhombic \k{appa}Ga2O3 films is confirmed by analyzing the STEM nano-diffraction pattern. The chemical composition, surface stoichiometry, and the bandgap energies of \k{appa}-Ga2O3 thin films grown on different substrates are studied by high resolution x-ray photoelectron spectroscopy (XPS) measurements. The type-II (staggered) band alignments at three interfaces between \k{appa}-Ga2O3 and c-sapphire, AlN, and YSZ substrates are determined by XPS, with the exception of \k{appa}-Ga2O3/GaN interface, which shows type I (straddling) band alignment.

With the development of the Internet, social media has become an important channel for posting disaster-related information. Analyzing attitudes hidden in these texts, known as sentiment analysis, is crucial for the government or relief agencies to improve disaster response efficiency, but it has not received sufficient attention. This paper aims to fill this gap by focusing on investigating attitudes towards disaster response and analyzing targeted relief supplies during disaster response. The contributions of this paper are fourfold. First, we propose several machine learning models for classifying public sentiment concerning disaster-related social media data. Second, we create a natural disaster dataset with sentiment labels, which contains nearly 50,00 Twitter data about different natural disasters in the United States (e.g., a tornado in 2011, a hurricane named Sandy in 2012, a series of floods in 2013, a hurricane named Matthew in 2016, a blizzard in 2016, a hurricane named Harvey in 2017, a hurricane named Michael in 2018, a series of wildfires in 2018, and a hurricane named Dorian in 2019). We are making our dataset available to the research community: https://github.com/Dong-UTIL/Natural-Hazards-Twitter-Dataset. It is our hope that our contribution will enable the study of sentiment analysis in disaster response. Third, we focus on extracting public attitudes and analyzing the essential needs (e.g., food, housing, transportation, and medical supplies) for the public during disaster response, instead of merely targeting on studying positive or negative attitudes of the public to natural disasters. Fourth, we conduct this research from two different dimensions for a comprehensive understanding of public opinion on disaster response, since disparate hazards caused by different types of natural disasters., Comment: 3 pages. The dataset is available on GitHub at this address: : https://github.com/Dong-UTIL/Natural-Hazards-Twitter-Dataset

For the need of improving the capacity of the geohazards monitoring, a professional monitoring system has been developed based on the Internet of things, WSN (Wireless Sensor Network) and network communication technology. The system consists of wireless sensing network, transmission network and data monitoring and analysis center. The WSN technology was used to organize network with displacement, tilt angle and rainfall in the wireless sensing network which could achieve perception and control all aspects of the monitoring area. The monitoring data can be transferred in two methods by the transmission network which was established based on the GSM and Beidou. The wireless sensing nodes can be controlled remotely by data monitoring and analysis center. For example, the acquisition interval can be modified remotely, the current data can be controlled to return immediately and sensing nodes can be controlled to entry into low power mode in order to save power, which means that Machine to Machine mode of geological disaster monitoring had been realized in the system.

Fresh e-commerce is a form of recently developed e-commerce that is coveted by many businesses. With the help of new retailing, fresh e-commerce has opened a new chapter in online marketing of online to offline models all around the world. However, with complications of competitors, business restructuring, drawbacks in technologies, and shortage of expertise, fresh ecommerce businesses are now in a period of critical innovation. Their own broadening advantages that are influencing the market are considered for ecommerce businesses. Due to this some of the biggest e-commerce giants in the world are competing to revolutionize the way people receive everyday items, specifically grocery products. This paper uses Amazon Fresh and Fresh Hema in the United States and China as two cases to explore the differences between countries, and to analyze the bottleneck of development in fresh e-commerce. Then, certain operation improvement to fresh ecommerce businesses have been suggested to improve the efficiency overall of the fresh e-commerce operation.

The horizontal section of the horizontal gas well will form a horizontally enlarged borehole due to factors such as the collapse of the well wall, and it is easy to form gas accumulation in the enlarged section, which will cause accidents such as overflow. Therefore, it is very important to study the gas accumulation law in the horizontal enlarged section. Based on the actual horizontal wellbore size, a three-dimensional horizontal rectangular-enlarged borehole model and a three-dimensional horizontal curved-enlarged borehole model are established in this paper to simulate the phenomenon of gas clustering in the enlarged diameter section. The research results show that, under the same length of the enlarged section, the gas discharge of the horizontally rectangular-enlarged borehole is difficult, which is more likely to cause gas accumulation, but the horizontally curved-enlarged borehole is less likely to cause gas accumulation; When the fluid flows through the horizontal enlarged diameter section, the pressure will increase and the pressure flowing out of the expansion section will decrease, and the faster the flow velocity, the greater the pressure in the expanding section.

Aimed at locating the temperature abnormal event of nuclear waste drums in a nuclear waste temporary storage repository by a Raman-based distributed temperature sensor, a principal component analysis (PCA)-based method for application is proposed. The effectiveness of the proposed method is verified in the physical simulation device of the nuclear waste drums. First, some samples of the temperature abnormal event with known location are taken as the reference samples, and their features are extracted by PCA. Then, the features of the test sample data to be located are also extracted by PCA. The Euclidean distance is used to measure the similarity between the features of the test sample and the feature of each reference sample. Finally, we find the reference sample that is most similar to a test sample, the location of which is considered the location of the temperature anomaly event for the test sample. The experimental results show that the proposed method can accurately locate the temperature abnormal event of the nuclear waste drums, and the accuracy rate can reach 96%. The method that is proposed in this paper can reliably locate the temperature abnormal event generated by the nuclear waste temporary storage repository induced by external factors such as landslides or earthquakes, and provide technical support for nuclear safety.