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This paper reviews materials challenges and recent progress for selective area regrowth and doping for vertical gallium nitride (GaN) power devices. The purpose is to realize randomly placed, reliable, contactable, and generally useable laterally patterned p-n junctions, which are the building blocks for various advanced power rectifiers and transistors. The general regrowth process and regrowth dynamics in trenches were discussed, where the effects of trench geometries, growth methods, and bulk substrates were elucidated. Comprehensive materials characterization techniques were utilized to analyze the regrown structures, including scanning electron microscopy, transmission electron microscopy, atom probe tomography, scanning probe microscopy, and secondary-ion mass spectrometry. Cathodoluminescence and secondary electrons in scanning electron microscopy and atom probe tomography were used to achieve lateral and vertical dopant profiling at a sub-micron scale. The regrowth interface after dry etching accumulated a high density of impurities and charges, contributing to the formation of a p+-n+ tunneling junction. This hypothesis was further confirmed by the electrostatic potential profile at the regrowth interface using electron holography. Novel etching technologies were investigated to improve the regrowth interface. It was found that low-power dry etching significantly reduced the interfacial charges and the reverse leakage currents of regrown p-n junctions. Photoelectrochemical wet etching was found to be effective in reducing deep-level defects near the regrowth interface. Atomic layer etching uses self-limiting chemical processes, thus removing the damaged layers without inducing further etching damage. Tertiarybutylchloride-based in situ etching may serve as an alternative etching method to dry etching with reduced etching damage. In terms of devices, regrown p-n junctions with low leakage currents and vertical junction field-effect transistors were demonstrated. Further improvements in selective area regrowth and associated devices can be expected using regrowth optimization and regrowth interface engineering via surface treatments and low-damage etching. These results represent an important step towards realizing selective area regrowth and doping for high performance GaN power electronics devices and systems.

Optical sources emitting in the ultraviolet (UV) to near-infrared wavelength range are an enabling tools for a wide variety of applications. To achieve broadband coherent generation within visible and UV spectrum, one fundamental obstacle is the strong material dispersion which limits efficient frequency conversion. Previous works have addressed this challenge by either using high input energies or delicate resonant structures. In this work, a simple device system is proposed to tackle the problem. Single crystalline aluminum nitride material with a threading dislocation density less than 109 cm–2 was used to provide broadband transparency, and a high order waveguide mode (transverse electric, TE10) was used to create anomalous dispersion near 800 nm, in which soliton fission processes are supported. As a result, supercontinuum generation from 490 nm to over 1100 nm with a second harmonic generated band covering from 407 to 425 nm is achieved with the total on-chip pulse energy of 0.6 nJ.

Vertical GaN-on-GaN Schottky barrier diodes based on as-grown and regrown samples were fabricated to investigate the effects of the etch-then-regrow process on device performance. The surface roughness increased slightly after dry etching and decreased after regrowth. According to X-ray diffraction results, the etch-then-regrow process caused a slight increase of defect density due to increased edge dislocations. Schottky parameters extracted from forward current-voltage curves, such as turn-on voltages of 0.74 V and 0.72 V, ideality factors of 1.07 and 1.10, and barrier heights of 1.07 eV and 1.05 eV, were obtained for diodes based on the regrown and as-grown samples, respectively. The breakdown voltage of the regrown sample was much lower than the as-grown sample. The regrowth interface can be regarded as a n-doping GaN layer due to the high interface charge density after the etch-then-regrown process. This equivalent ${n}$ -doping GaN layer reduced the effective thickness of the UID-GaN under the Schottky contact thus causing lower breakdown voltage for the regrown sample. Poole-Frenkel emission and trap-assisted tunneling processes were responsible for the leakage of both as-grown and regrown samples according to the temperature dependence of the reverse currents.

Background Identification of vertebral fractures (VFs) is critical for effective secondary fracture prevention owing to their association with the increasing risks of future fractures. Plain abdominal frontal radiographs (PARs) are a common investigation method performed for a variety of clinical indications and provide an ideal platform for the opportunistic identification of VF. This study uses a deep convolutional neural network (DCNN) to identify the feasibility for the screening, detection, and localization of VFs using PARs. Methods A DCNN was pretrained using ImageNet and retrained with 1306 images from the PARs database obtained between August 2015 and December 2018. The accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve (AUC) were evaluated. The visualization algorithm gradient-weighted class activation mapping (Grad-CAM) was used for model interpretation. Results Only 46.6% (204/438) of the VFs were diagnosed in the original PARs reports. The algorithm achieved 73.59% accuracy, 73.81% sensitivity, 73.02% specificity, and an AUC of 0.72 in the VF identification. Conclusion Computer driven solutions integrated with the DCNN have the potential to identify VFs with good accuracy when used opportunistically on PARs taken for a variety of clinical purposes. The proposed model can help clinicians become more efficient and economical in the current clinical pathway of fragile fracture treatment.

This paper reports a comprehensive study on the anisotropic electrical properties of vertical ( $\overline {\textsf {2}}01$ ) and (010) $\beta $ -Ga2O3 Schottky barrier diodes (SBDs). The devices were fabricated on single-crystal substrates grown by an edge-defined film-fed growth method. The temperature-dependent current–voltage (I–V) and capacitance–voltage (C–V) characteristics were systematically measured, analyzed, and compared. The ( $\overline {\textsf {2}}01$ ) and (010) SBDs exhibited on-resistances ( ${R}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) of 0.56 and $0.77~\textsf {m}\Omega \cdot \textsf {cm}^{{\textsf {2}}}$ , turn- ON voltages ( ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ ) of 1.0 and 1.3 V, Schottky barrier heights (SBHs) of 1.05 and 1.20 eV, electron mobilities of 125 and 65 cm2/( $\textsf {V}\cdot ~\textsf {s}$ ), respectively, with an on-current of ~1.3 kA/cm2 and on/off ratio of ~109. The (010) SBD had a larger ${V}_{{ \mathrm{\scriptscriptstyle ON}}}$ and SBH due to anisotropic surface properties (i.e., surface Fermi level pinning and band bending), as supported by X-ray photoelectron spectroscopy measurements. Temperature-dependent I–V also revealed the inhomogeneous nature of the SBH in both devices, where the ( $\overline {\textsf {2}}01$ ) SBD showed a more uniform SBH distribution. The homogeneous SBH was also extracted: 1.33 eV for the ( $\overline {\textsf {2}}01$ ) SBD and 1.53 eV for the (010) SBD. The reverse leakage current of the devices was well described by the two-step trap-assisted tunnelingmodel and the 1-D variable range hopping conduction model. The ( $\overline {\textsf {2}}01$ ) SBD showed a larger leakage current due to its lower SBH and/or smaller activation energy, and thus a smaller breakdown voltage. These results indicate that the crystalline anisotropy of $\beta $ -Ga2O3 can affect the electrical properties of vertical SBDs and should be taken into consideration when designing $\beta $ -Ga2O3 electronics.

This letter reports the first implementation of a hydrogen-plasma-based edge termination technique (HPET) in vertical GaN p-n power diodes grown on bulk GaN substrates using metalorganic chemical vapor deposition. The device with a 9- $\mu \text{m}$ -thick drift layer exhibited a high breakdown voltage ( ${V}_{\textsf {bd}}$ ) of 1.57 kV, a low ON-resistance ( ${R}_{\mathrm{ ON}}$ ) of 0.45 $\text{m}\Omega ~ \cdot $ cm2 (or 0.70 $\text{m}\Omega ~\cdot $ cm2 with current spreading considered) and a high Baliga’s figure-of-merit ( ${V}^{\textsf {2}}_{\textsf {bd}}/{R}_{\mathrm{ ON}}$ ) of 5.5 GW/cm2 (or 3.6 GW/cm2) without passivation or field plate, which are close to the theoretical limit of GaN. This technique enabled a significant reduction in leakage current (~106 times at −300 V) and a huge enhancement in ${V}_{\textsf {bd}}$ (from ~300 V to 1.57 kV). Furthermore, the device showed good forward characteristics with a turn-ON voltage of 3.5 V, an ON-current of ~2 kA/cm2 (or 1.3 kA/cm2), an ON/OFF ratio of ~109, and an ideality factor of 1.4. This work shows the HPET can serve as an effective, low cost, and easy-to-implement edge termination technique for high voltage and high power GaN p-n power diodes.

We demonstrated an integrated biosensor with a thin film transistor for recording electrical charges carried by bio-molecules and a microfluidic channel for detecting diffusion properties of the target solution. Using streptavidin and biotin as examples, the sensor is able to detect the binding interaction of streptavidin-biotin complexes by monitoring the transient responses of the transistor current. Our approach can be applied to the field of detection of protein–protein interactions.

Potholes, one of the major types of distress on pavement surfaces, damage vehicles and are a safety hazard for the travelling public. In order to mitigate the effect of potholes, cold-mix asphalt (CMA) patching materials are commonly used for urgent repair of pavement surfaces before resurfacing can be undertaken. Therefore, the short-term (initial stability) and long-term (in-service durability) performance evaluation of CMA patching materials is necessary. This study conducted several curing conditions in the laboratory to investigate short-term, long-term, and moisture effects on pavement surfaces. Moreover, this study compared the Marshall stability of samples prepared under various compaction conditions. Marshall stability, Cantabro abrasion, and UK wheel tracking tests were conducted to evaluate the performance of CMA patching materials. The results indicated that the Marshall stability of dense-gradation (DG) CMA patching materials was higher than that of open-graded (OG) CMA patching materials and the Marshall stability of OG CMA patching materials was highly influenced by the coarse aggregate proportion. The DG and OG CMA patching materials exhibited comparable abrasion resistance, and the Cantabro abrasion ratio was highly correlated to the estimated asphalt film thickness for the OG CMA patching materials. A moisture indicator (MI) was proposed, and the effect of moisture damage on Marshall stability and Cantabro abrasion ratio was related to the proposed MI. The rutting resistance of the DG CMA patching materials was higher than that of the OG CMA patching materials, which is consistent with the Marshall stability result.

We report the first demonstration of beta-phase gallium oxide optical waveguides on sapphire in the ultraviolet to near-infrared spectra. A low propagation loss of 3.7 dB/cm was obtained at the wavelength of 810 nm

In this work, we study the crystalline defect induced optical scattering loss inside photonic waveguide. Volume current method is implemented with a close form of dyadic Green’s function derived. More specifically, threading dislocation induced scattering loss inside AlN waveguides in UV–visible spectrum wavelengths are studied since this material is intrinsically accompanied with high densities of dislocations (typically on order of 108–1010cm−2). The results from this study reveal that threading dislocations contribute significant amount of scattering loss when material is not MOCVD grown. Additionally, the scattering loss is strongly dependent on polarization and waveguide geometries: TM modes exhibit higher scattering loss compared with TE modes, and the multimode large core waveguides are more susceptible to threading dislocations compared with single mode waveguides and high-aspect-ratio waveguides. Conclusions from this work can be supported by several recently published investigations on III-N based photonic devices. The model derived from this work can also be easily altered to fit other material systems with other types of crystalline defects.

The development of gallium nitride (GaN) power devices requires a reliable selective-area doping process, which is difficult to achieve because of ongoing challenges associated with the required etch-then-regrow process. The presence of silicon (Si) impurities of unclear physical origin at the GaN regrowth interface has proven to be a major bottleneck. This paper investigates the origin of Si contamination at the epitaxial GaN-on-GaN interface and demonstrates an approach that markedly reduces its impact on device performance. An optimized dry-etching approach combined with UV-ozone and chemical etching is shown to greatly reduce the Si concentration levels at the regrowth interface, and a significant improvement in a reverse leakage current in vertical GaN-based p–n diodes is achieved.

A transistor-based biosensor with high sensitivity is demonstrated in this paper. The sensor is composed of a reusable In–Ga–ZnO (IGZO)-thin-film transistor (TFT) array wire connected to an external sensing pool. The TFT acts as an electrical charge transducer as well as the signal readout device. Contrast to typical approachesofemploying parameters, such as transconductance, threshold voltage, or current change as the benchmark for sensitivity, we develop a model to extract the corresponding electrical changes after introducing analytes so as tomitigate device-to-device sensing variations. Using Epstein–Barr nuclear antigen-1 (EBNA-1) antibody as the example of target analyte, the IGZO-TFT biosensors are able to selectively detect 10 pg/mL of EBNA-1 antibody in the phosphate-buffered saline solution. The measurement results were cross verifiedwith conventional enzyme-linked immunosorbent assay (ELISA). Our approach is four orders of magnitude better than the ELISA.

AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) were fabricated on Si substrates with a 10 nm boron nitride (BN) layer as a gate dielectric deposited by electron cyclotron resonance microwave plasma chemical vapor deposition. The material characterization of the BN/GaN interface was investigated by X-ray photoelectric spectroscopy (XPS) and UV photoelectron spectroscopy. The BN bandgap from the B1s XPS energy loss is ∼5 eV consistent with sp2 bonding. The MISHEMTs exhibit a low off-state current of 1 × 10−8 mA/mm, a high on/off current ratio of 109, a threshold voltage of −2.76 V, a maximum transconductance of 32 mS/mm at a gate voltage of −2.1 V and a drain voltage of 1 V, a subthreshold swing of 69.1 mV/dec, and an on-resistance of 12.75 Ω·mm. The interface state density (Dit) is estimated to be less than 8.49 × 1011 cm−2 eV−1. Gate leakage current mechanisms were investigated by temperature-dependent current–voltage measurements from 300 K to 500 K. The maximum breakdown electric field is no less than 8.4 MV/cm. Poole–Frenkel emission and Fowler–Nordheim tunneling are indicated as the dominant mechanisms of the gate leakage through the BN gate dielectric at low and high electric fields, respectively.

This work reports on a comprehensive examination of the electrical and thermal properties of vertical Schottky diodes fabricated on ( 2 ¯ 01 )- and (001)-oriented samples of β-Ga2O3. The temperature-dependent current–voltage (I–V) and capacitance–voltage (C–V) data were gathered and analyzed down to 60 K. Deep level transient spectroscopy (DLTS) was used to study bulk and interface defects in the two materials from approx. 325 K down to 60 K. In the bulk ( 2 ¯ 01 ) material, an electron trap was observed at EC−0.46 eV, with a capture cross section of 1.6 × 10−14 cm2 and a lambda-corrected maximum trap density of 9.08 × 1015 cm−3. These results and others indicate that the electron trap is a strong candidate for the well-known E1 defect in β-Ga2O3 based on recent investigations. Additionally, in the ( 2 ¯ 01 ) material, the smooth modulation typical of interface states is evident at temperatures below 275 K. The (001) samples manifested what is likely the E2* electron trap at EC−0.68 eV, with a capture cross section of 1.64 × 10−15 cm2 and a lambda-corrected maximum trap density of 8.85 × 1015 cm−3. The presence of the E2* defect, in particular, is a contrast to the findings of recent DLTS investigations on β-Ga2O3, which report that E2* emerged only after low-energy proton irradiation. These results help to further map out the defect signatures found in β-Ga2O3 materials, which are of vital importance in the design and fabrication of future β-Ga2O3 devices.

Nonpolar InGaN/GaN quantum wells (QWs) have gained significance for efficient light emitting since it eliminates polarization-related effects and allows for higher radiative capability. Although much progress has been made in analyzing carrier localization effects at cryogenic temperatures, carrier dynamics at above room temperatures are still not well understood. In this work, we have observed and explored anomalous carrier dynamics of two nonpolar m-plane InGaN/GaN QWs at high temperatures by combining scanning transmission electron microscopy (STEM) and photophysical characterization. Both experimental and theoretical results suggest that carrier lifetime in both samples increases with temperature in a certain range of temperature. However, the reduced integrity and uniformity of QWs make carriers more prone to the nonradiative Shockley-Reed-Hall recombination as temperature rises. Moreover, both acoustic and optical phonon scatterings dominate from 300 to 600 K through the analysis on the evolution of photoluminescence spectra. Overall, these detailed studies provide insights into approaches to evaluate carrier dynamics at elevated temperatures and improve emitting performance to further push the practical efficiency limit.

We demonstrate a nickel/insulating-GaN (i-GaN)/p-type GaN junction and investigate its electrical properties. The i-GaN is formed by exposure to a low-power hydrogen plasma to passivate the p-GaN layer. Cathodoluminescence spectroscopy of the i-GaN is used to understand the passivation effect of the hydrogen plasma on p-GaN. The junction shows very low leakage (

The graphics processing unit (GPU) is widely used in applications that require massive computing resources such as big data, machine learning, computer vision, etc. As the diversity of applications grows, the GPU’s performance becomes difficult to maintain by its warp scheduler. Most of the prior studies of the warp scheduler are based on static analysis of GPU hardware behavior for certain types of benchmarks. We propose for the first time (to the best of our knowledge), a machine learning approach to intelligently select suitable policies for various applications in runtime. The simulation results indicate that the proposed approach can maintain performance comparable to the best policy across different applications.

This paper proposes a deep learning based wearable medicines recognition system for visually impaired people. The proposed system is composed of a pair of wearable smart glasses, a wearable waist-mounted drug pills recognition device, a mobile device application, and a cloud-based management platform. The proposed system uses deep learning technology to identify drug pills to avoid taking wrong drugs. The experimental results show that the accuracy of the proposed system has reached up to 90% that can really be achieved the purpose of correct medication for visually impaired people.

We report the demonstration of a steep-slope field-effect transistor with AlGaN/GaN MIS-HEMTs employing SiO2-based threshold switching devices in series with the source. The SiO2-based threshold switching devices exhibited steep slope when changing resistance states. The integrated steep-slope transistor showed a low subthreshold swing of sub-5 mV/dec with a transition range of over 105 in the transfer characteristics in both sweep directions at room temperature, as well as the low leakage current (10-5 μA μm-1) and a high I ON/I OFF ratio (>107). Moreover, with the SiO2-based threshold switching devices we also observed a positive shift of threshold voltages of the integrated device. Results from more than 50 transfer characteristics measurements also indicate the good repeatability and practicability of such a steep-switching device, where the average steep slopes are below 10 mV/decade. This steep-slope transistor with oxide-based threshold switching devices can be further extended to various transistor platforms like Si and III-V and are of potential interest for the development of power switching and high frequency devices.

The driving force behind software development of the Electronic Medical Record (EMR) has been gradually changing. Heterogeneous software requirements have emerged, so how to correctly carry out development project has become a complex task. This paper adopts the knowledge engineering and management mechanism, i.e., CommonKADS, and software quality engineering to improve existing strategic information management (SIM) plan as a design methodology to help software implementation for medical institutes. We evaluate the adopting performance by a real case that examines the maturity level of the architecture alignment between the target solution in the proposed SIM plan and the built medical system. This proposed methodology can be used to improve the SIM plan.With the proposed SIM plan, software development process is improved.The related software architecture is examined in different models.A real case with the working scenario to verify this proposed SIM plan.

We perform comprehensive studies on the fundamental loss mechanisms in III-nitride waveguides in the visible spectral region. Theoretical analysis shows that free carrier loss dominates for GaN under low photon power injection. When optical power increases, the two photon absorption loss becomes important and eventually dominates when photon energy above half-bandgap of GaN. When the dimensions of the waveguides reduce, the sidewall scattering loss will start to dominate. To verify the theoretical results, a high performance GaN-on-sapphire waveguide was fabricated and characterized. Experimental results are consistent with the theoretical findings, showing that under high power injection the optical loss changed significantly for GaN waveguides. A low optical loss ~2 dB/cm was achieved on the GaN waveguide, which is the lowest value ever reported for the visible spectral range. The results and fabrication processes developed in this work pave the way for the development of III-nitride integrated photonics in the visible and potentially ultraviolet spectral range for nonlinear optics and quantum photonics applications.

Information security management plays an essential role for drawing the roadmap of information security; thus, many theoretical methodologies and practical standards are brought into this domain. However, many standards and methodologies are too cumbersome to be adopted by an organization. Additionally, there is no unified framework to systematically handle the tedious tasks of information security management. This study’s primary goal is to design an integrated system for information security management (ISISM) that aims to use current methodologies and standards to solve the above-mentioned issues. Because business impact analysis and risk analysis are the most important areas within this domain, we carefully select the related methods and then integrate them into a unified framework, upon which the proposed ISISM depends. To achieve this outcome for this study, security requirement engineering is adopted, which enables the designed system to support system users in generating risk assessment reports wi...

In this paper, we report the fabrication of low loss beta-phase gallium oxide (β-Ga2O3) optical waveguides and the propagation loss analysis of the waveguides in the ultraviolet (UV) to near infrared (NIR) spectral region. The β-Ga2O3 thin films were grown on sapphire substrates using metal organic chemical vapor deposition and were fabricated into various waveguide structures using nanofabrication processes. A low propagation loss of 3.7 dB/cm was obtained on the β-Ga2O3 waveguide at the wavelength of 810 nm, which is comparable to the state of the art. Combined with theoretical simulations, various loss mechanisms from two-photon absorption, sidewall scattering, top surface scattering, and bulk scattering were discussed for β-Ga2O3 waveguides, and their contributions to the total optical loss were estimated. These results show that β-Ga2O3 is a promising optical material for the fabrication of various integrated photonic devices in the UV–NIR spectra region.

Low-damage, low-temperature, and easy-to-implement hydrogen-plasma-based termination is attractive for fabricating implantation- and etching-free GaN power p–n diodes. This work investigates in detail the hydrogenation process and unveils the critical role of thermal annealing. A subsequent thermal annealing is key to thermally driving down hydrogen to fully hydrogenate p-GaN to form the termination. The devices showed a specific on-resistance of 0.4 mΩ cm2 and a breakdown voltage (BV) of ~1.4 kV. They also exhibited improved BV compared with mesa-etched devices. High temperature performance was also investigated. These results can serve as important references for future developments of GaN power electronics.

This work demonstrates the construction of p-n heterojunctions between mechanically exfoliated beta-phase gallium oxide (β-Ga2O3) and p-GaN. The detailed mechanical exfoliation process was developed and can be used for further device applications. The atomic force microscopy study showed that the exfoliated β-Ga2O3 flakes had a very smooth surface with a roughness of 0.65 nm. Transmission electron microscopy revealed a clearly defined interface between the exfoliated β-Ga2O3 and p-GaN. The p-n heterojunction exhibited a turn-on voltage of 3.6 V and a rectification ratio of ∼105. The heterojunction also showed good thermal performance up to 200 °C. Ideality factors and turn-on voltages decrease with temperature, tending toward the ideal threshold voltage of 3.2 V as determined by Silvaco simulations. This work provides valuable information on a mechanically exfoliated β-Ga2O3/GaN p-n heterojunction, which opens up the opportunities for a variety of photonic and electronic applications.

The paper presents a low temperature (with 60 °C) inkjet printing and filling process to realize low resistive Ag TSV (Through Substrate Vias) with the aspect ratio of via depth vs. diameter from 2 to 5 in a SU-8 substrate potential for flexible microsystem packaging applications. Combining humidity control and layer-by-layer Ag mirror reaction, the proposed process technology can accomplish a fully filled TSV with the lowest electrical resistivity of ∼450 μΩ•cm in comparison with the prior printing and filling technologies.

Color is one of the most important modality to convey information. However, around the world about 200 million people are with color vision deficiency (CVD). Some works have been developed to improve viewing experience for people with CVD, such as simulating colorblind vision, re-coloring images, and using patterns to encode images. In this work, we advocate that combining re-coloring and adding patterns to image might be more helpful to colorblind people and is worth deep research. We propose a framework to combine patterns and re-coloring. We first simulate colorblind vision, determine how to add patterns according to the degree of deformation, and then re-color images overlaid with patterns. In the evaluation, we verify effectiveness of combining adding patterns and re-coloring, and demonstrate content-dependent characteristics through the studies based on different types of images and different types of patterns.

We report, for the first time, the characterizations on optical nonlinearities of beta-phase gallium oxide (\b{eta}-Ga2O3), where both (010) \b{eta}-Ga2O3 and (-201) \b{eta}-Ga2O3 were examined for two-photon absorption (TPA) coefficient, Kerr refractive index, and their polarization dependence. The wavelength dependence of the TPA coefficient and Kerr refractive index was estimated using a widely used analytical model. \b{eta}-Ga2O3 exhibits a TPA coefficient of 1.2 cm/GW for (010) \b{eta}-Ga2O3 and 0.58 cm/GW for (-201) \b{eta}-Ga2O3. The Kerr refractive index is -2.14*10^(15) cm2/W for (010) \b{eta}-Ga2O3 and -2.89*10^(15) cm2/W for (-201) \b{eta}-Ga2O3. In addition, \b{eta}-Ga2O3 shows stronger nonlinear optical anisotropy on the (-201) plane than on the (010) plane, possibly due to highly asymmetric crystal structure. Compared with that of gallium nitride (GaN), the TPA coefficient of \b{eta}-Ga2O3 is 20 times smaller, and the Kerr refractive index of \b{eta}-Ga2O3 is also found to be 4 to 5 times smaller. These results indicate that \b{eta}-Ga2O3 has the potential for use in ultra-low loss waveguides and ultra-stable resonators and integrated photonics, especially in the UV and visible wavelength spectral range.

Different well widths of m-plane Mg0.19Zn0.81O / ZnO multiple quantum wells (MQWs) have been fabricated on the two-step pregrown MgZnO-buffered m-plane sapphires by a pulsed laser deposition and have a narrower linewidth on x-ray diffraction than ZnO-buffered MQWs. By using the variation method to calculate the band diagram and by corroborating the results of temperature-dependent photoluminescence, we confirm the binding energies of free exciton and basal-stacking-fault-bound exciton, which is composed of electrons in the barrier and confined hole in the narrow-width MQWs. The coupling of A1(LO) phonon with excitons in m-MQWs shows more sensitivity toward a decrease in well width than E2(low), due to the crystal symmetry and the reduced Bohr radius.

Beta-phase gallium oxide (β-Ga2O3) Schottky barrier diodes were fabricated on highly doped single-crystal substrates, where their temperature-dependent electrical properties were comprehensively investigated by forward and reverse current density – voltage and capacitance – voltage characterization. Both the Schottky barrier height and the ideality factor showed a temperature-dependence behavior, revealing the inhomogeneous nature of the Schottky barrier interface caused by the interfacial defects. With a voltage-dependent Schottky barrier incorporated into thermionic emission theory, the inhomogeneous barrier model can be further examined. Furthermore, the reverse leakage current was found to be dominated by the bulk leakage currents due to the good material and surface quality. Leakage current per distance was also obtained. These results can serve as important references for designing efficient β-Ga2O3 electronic and optoelectronic devices on highly doped substrates or epitaxial layers.

To mimic selective-area doping, p-GaN was regrown on an etched GaN surface on GaN substrates by metalorganic chemical vapor deposition. Vertical GaN-on-GaN p-n diodes were fabricated to investigate the effects of the etch-then-regrowth process on device performance. The crystal quality of the sample after each epitaxial step was characterized by X-ray diffraction, where the etch-then-regrowth process led to a very slight increase in edge dislocations. A regrowth interfacial layer was clearly shown by transmission electron microscopy. Strong electroluminescence was observed with three emission peaks at 2.2 eV, 2.8 eV, and 3.0 eV. The forward current density increased slightly with increasing temperature, while the reverse current density was almost temperature independent indicating tunneling as the reverse transport mechanism. This result is very similar to the reported Zener tunnel diode comprising a high doping profile at the junction interface. High levels of silicon and oxygen concentrations were observed at the regrowth interface with a distribution width of ∼100 nm. This work provides valuable information on p-GaN regrowth and regrown GaN p-n diodes, which can serve as an important reference for developing selective doping for advanced GaN power electronics for high voltage and high power applications.

We report nonpolar vertical GaN-on-GaN p–n diodes grown on m-plane free-standing substrates. Cathodoluminescence measurements showed that the nonpolar p-GaN had a high quality with very few deep-level states. The device exhibited good rectifying behaviors with a turn-on voltage of 4.0 V, on-resistance of 2.3 mΩcm2, and high on/off ratio of 1010. The reverse current leakage was described by a trap-assisted space-charge-limited current conduction mechanism. The critical electrical field was calculated to be 2.0 MV/cm without field plates or edge termination. These results pave the way for development of novel nonpolar power electronics and polarization-engineering-related advanced power devices.

In this paper, we perform a comprehensive study on energy band engineering of InGaN multi-quantum-well (MQW) solar cells using AlGaN electron- and hole-blocking layers. InGaN MQW solar cells with AlGaN layers were grown by metalorganic chemical vapor deposition, and high crystal quality was confirmed by high resolution X-ray diffraction measurements. Time-resolved photoluminescence results showed that the carrier lifetime on the solar cells with AlGaN layers increased by more than 40% compared to that on the reference samples, indicating greatly improved carrier collections. The illuminated current-density (J–V) measurements further confirmed that the short-circuit current density (Jsc) of the solar cells also benefited from the AlGaN layer design and increased 46%. At room temperature, the InGaN solar cells with AlGaN layers showed much higher power conversion efficiency (PCE), by up to two-fold, compared to reference devices. At high temperatures, these solar cells with AlGaN layers also delivered superior photovoltaic (PV) performance such as PCE, Jsc, and fill factor than the reference devices. These results indicate that band engineering with AlGaN layers in the InGaN MQW solar cell structures can effectively enhance the carrier collection process and is a promising design for high efficiency InGaN solar cells for both room temperature and high temperature PV applications.

We investigate the thermal stability of InGaN solar cells under thermal stress at elevated temperatures from 400 °C to 500 °C. High Resolution X-Ray Diffraction analysis reveals that material quality of InGaN/GaN did not degrade after thermal stress. The external quantum efficiency characteristics of solar cells were well-maintained at all temperatures, which demonstrates the thermal robustness of InGaN materials. Analysis of current density–voltage (J–V) curves shows that the degradation of conversion efficiency of solar cells is mainly caused by the decrease in open-circuit voltage (Voc), while short-circuit current (Jsc) and fill factor remain almost constant. The decrease in Voc after thermal stress is attributed to the compromised metal contacts. Transmission line method results further confirmed that p-type contacts became Schottky-like after thermal stress. The Arrhenius model was employed to estimate the failure lifetime of InGaN solar cells at different temperatures. These results suggest that while InGaN solar cells have high thermal stability, the degradation in the metal contact could be the major limiting factor for these devices under high temperature operation.

The enzyme kinetic in a biochemical reaction is critical to scientific research and drug discovery but can hardly be determined experimentally from enzyme assays. In this work, a charge-current transducer (a transistor) is proposed to evaluate the status of biochemical reaction by monitoring the electrical charge changes. Using the malate-aspartate shuttle as an example, a thin-film transistor (TFT)-based biosensor with an extended gold pad is demonstrated to detect the biochemical reaction between NADH and NAD+. The drain current change indicates the status of chemical equilibrium and stoichiometry.