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InGaN-ZnSnN2 based quantum wells (QWs) structure is proposed and studied as an active region for high efficiency amber (λ ∼ 600 nm) light emitting diodes (LEDs), which remains a great challenge in pure InGaN based LEDs. In the proposed InGaN-ZnSnN2 QW heterostructure, the thin ZnSnN2 layer serves as a confinement layer for the hole wavefunction utilizing the large band offset at the InGaN-ZnSnN2 interface in the valence band. The barrier layer is composed of GaN or AlGaN/GaN in which the thin AlGaN layer is used for a better confinement of the electron wavefunction in the conduction band. Utilizing the properties of band offsets between ZnSnN2 and InGaN, the design of InGaN-ZnSnN2 QW allows us to use much lower In-content (∼10%) to reach peak emission wavelength at 600 nm, which is unachievable in conventional InGaN QW LEDs. Furthermore, the electron-hole wavefunction overlap (Γe-h) for the InGaN-ZnSnN2 QW design is significantly increased to 60% vs. 8% from that of the conventional InGaN QW emitting at the same wavelength. The tremendous enhancement in electron-hole wavefunction overlap results in ∼225× increase in the spontaneous emission radiative recombination rate of the proposed QW as compared to that of the conventional one using much higher In-content. The InGaN-ZnSnN2 QW structure design provides a promising route to achieve high efficiency amber LEDs. [ABSTRACT FROM AUTHOR]

The effect of inserting a nm-scale layer of Zn(Si,Ge)N2 into an AlGaN quantum well structure designed for light emission in the wavelength range from 255 to 305 nm is investigated here. The enhanced confinement of the hole within the quantum well results in an enhancement of the overlap of the hole and electron wave functions, resulting in an enhancement of the radiative recombination rate. In this theoretical calculation, for emission at a 270 nm wavelength, the enhancement in the wavefunction overlap can reach a factor of 7 when compared to an AlGaN quantum well device specifically engineered for optimal emission at the identical wavelength. Increases of almost an order of magnitude in both the peak spontaneous emission intensity and the radiative recombination rate are predicted. The peak emission wavelength can be tuned from 255 to 305 nm by adjusting the width and/or the composition of the inserted layer. The proposed structures provide a route to higher efficiency ultraviolet practical light emitting diodes and lasers. [ABSTRACT FROM AUTHOR]

Beta gallium oxide (β-Ga2O3) is an emerging ultrawide bandgap (∼4.8 eV) semiconductor with attractive properties for future power and radio frequency (RF) electronics, optoelectronics, and sensors for detecting gases and solar-blind ultraviolet radiation. Beyond such promises, β-Ga2O3 crystal possesses excellent mechanical properties, making it pertinent as a material for micro/nanoelectromechanical systems (M/NEMS). Here, we present an overview and perspective on the emerging β-Ga2O3 M/NEMS and their roles in supplementing Ga2O3 power and RF electronics. We review the development of β-Ga2O3 micro/nanomechanical devices and precise extraction of mechanical properties from these devices. We evaluate the design for frequency scaling up to over 4 GHz by tuning the device geometry and dimensions. Toward technological applications, β-Ga2O3 M/NEMS are analyzed in two aspects: β-Ga2O3 vibrating channel transistors for potential integration with β-Ga2O3 power and RF electronics with operating frequency beyond 1 GHz, and β-Ga2O3 resonant transducers for photon radiation detection with scaling of responsivity and response time. With analytical prediction, we envision challenges and propose strategies and schemes in efficient electromechanical transduction engineering, frequency scaling, and design and fabrication for future development of β-Ga2O3 M/NEMS. [ABSTRACT FROM AUTHOR]

Si-doped β-phase (010) Ga2O3 epi-films with fast growth rates were comprehensively investigated using trimethylgallium (TMGa) as the Ga precursor via metalorganic chemical vapor deposition (MOCVD). Two main challenges facing the MOCVD growth of thick (010) β-Ga2O3 films with fast growth rates include high impurity carbon (C) incorporation and rough surface morphologies due to the formation of imbedded 3D pyramid-shaped structures. In this work, two different categories of oxygen source (high-purity O2 > 99.9999% and O2* with 10 ppm of [H2O]) were used for β-Ga2O3 MOCVD growth. Our study revealed that the size and density of the 3D defects in the β-Ga2O3 epi-films were significantly reduced when the O2* was used. In addition, the use of off-axis (010) Ga2O3 substrates with 2° off-cut angle leads to further reduction of defect formation in β-Ga2O3 with fast growth rates. To suppress C incorporation in MOCVD β-Ga2O3 grown with high TMGa flow rates, our findings indicate that high O2 (or O2*) flow rates are essential. Superior room temperature electron mobilities as high as 110–190 cm2/V·s were achieved for β-Ga2O3 grown using O2* (2000 sccm) with a growth rate of 4.5 μm/h (film thickness of 6.3 μm) within the doping range of 1.3 × 1018–7 × 1015 cm−3. The C incorporation is significantly suppressed from ∼1018 cm−3 to <5 × 1016 cm−3 ([C] detection limit) for β-Ga2O3 grown using high O2 (O2*) flow rate of 2000 sccm. Results from this work will provide guidance on developing high-quality, thick β-Ga2O3 films required for high power electronic devices with vertical configurations. [ABSTRACT FROM AUTHOR]

We report on the nondestructive measurement of Young's modulus of thin-film single crystal beta gallium oxide (β-Ga2O3) out of its nanoscale mechanical structures by measuring their fundamental mode resonance frequencies. From the measurements, we extract the Young's modulus in the (100) plane, EY,(100) = 261.4 ± 20.6 GPa, for β-Ga2O3 nanoflakes synthesized by low-pressure chemical vapor deposition (LPCVD), and in the [010] direction, EY,[010] = 245.8 ± 9.2 GPa, for β-Ga2O3 nanobelts mechanically cleaved from bulk β-Ga2O3 crystal grown by the edge-defined film-fed growth (EFG) method. The Young's moduli extracted directly on nanomechanical resonant device platforms are comparable to theoretical values from first-principle calculations and experimentally extracted values from bulk crystal. This study yields important quantitative nanomechanical properties of β-Ga2O3 crystals and helps pave the way for further engineering of β-Ga2O3 micro/nanoelectromechanical systems (M/NEMS) and transducers. [ABSTRACT FROM AUTHOR]

Staggered InGaN quantum wells (QWs) are analyzed as improved gain media for laser diodes (LDs) lasing at 440 and 500 nm. The calculation of band structure is based on a 6-band k·p method taking into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to enhance the optical gain as well as to reduce the threshold current density for LDs emitting at 440 and 500 nm. Our analysis shows that the optical gain is enhanced by 1.5–2.1 times by utilizing the staggered InGaN QW active region emitting at 440 nm, which leads to a reduction of the threshold current density up to 24% as compared to that of the conventional InGaN QW laser. Staggered InGaN QWs with enhanced optical gain shows significantly reduced blue-shift as carrier density increases, which enables nitride QWs with high optical gain in the green spectral regime. The use of green-emitting three-layer staggered InGaN QW is also expected to lead to reduction in the threshold carrier density by 30%. [ABSTRACT FROM AUTHOR]

Type-II InGaN–GaNAs quantum wells (QWs) with thin dilute-As (∼3%) GaNAs layer are analyzed self-consistently as improved III-nitride gain media for diode lasers. The band structure is calculated by using a six-band k·p formalism, taking into account valence band mixing, strain effect, spontaneous and piezoelectric polarizations, as well as the carrier screening effect. The type-II InGaN–GaNAs QW structure allows large electron-hole wave function overlap by confining the hole wave function in the GaNAs layer of the QW. The findings based on self-consistent analysis indicate that type-II InGaN-GaNAs QW active region results in superior performance for laser diodes, in comparison to that of conventional InGaN QW. Both the spontaneous emission radiative recombination rate and optical gain of type-II InGaN–GaNAs QW structure are significantly enhanced. Reduction in the threshold current density of InGaN–GaNAs QW lasers is also predicted. [ABSTRACT FROM AUTHOR]

Functional fluorescent silkworm silk holds promise for many important applications in biomedical engineering, optics, and photonics. However, it remains a challenge to obtain fluorescent silk in scale-up with both good mechanical properties and highly stable fluorescence simultaneously. In this work, we report a highly efficient strategy to produce fluorescent silk through directly feeding silkworm larvae with graphene quantum dots or CdSe/ZnS core–shell quantum dots. The obtained quantum dots-reinforced luminescent silkworm silk has superior mechanical strength and toughness, stable fluorescence, and good biocompatibility in comparison with the normal or fluorescent dye-colored silk. The strategy proposed in this work is environmental and economical and, also importantly, can generate superior luminescent silks in large scale. This study also provides possible cues for fabricating durable, fluorescent microdevices, and fabrics. [ABSTRACT FROM AUTHOR]

The formation of a broadband photodetector with high response, high sensitivity and controllable band is a major challenge to improve the application range of photodetectors. The integration of quantum dots and highly conductive materials is one of the important approach for the application of broadband photodetectors. In this work, ultraviolet–visible–near infrared (UV–Vis–NIR) sensitive PD consisting of ZnO film/PbS quantum dots (QDs) heterostructure was proposed. While forming a built-in electric field, the heterostructure also generates a barrier to prevent carrier recombination, so that the heterostructure PD has excellent photoresponse performance in the UV–Vis–NIR range, and the peak responsivity is increased by 550%. Increased from 0.974 mA/W to 6.332 mA/W, accompanied by obvious red shift, faster response and recovery speed compared to pure ZnO film PD. Different from other experiments, in order to make the performance gain of PbS QDs on ZnO film more obvious and intuitive, this article uses RF magnetron sputtering to prepare ultra-thin ZnO film, and discusses the impact of PbS QDs on the photoelectric properties of ZnO film more comprehensively and systematically. The performance of the broad spectrum in this experiment will be of great help to the research and application of ZnO PD in the future. • Ultraviolet–visible–near infrared (UV–Vis–NIR) sensitive PD consisting of ZnO film/PbS quantum dots (QDs) heterostructure was proposed. • While forming a built-in electric field, the heterostructure also generates a barrier to prevent carrier recombination, so that the heterostructure PD has excellent photoresponse performance in the UV–Vis–NIR range, and the peak responsivity is increased by 550%. Increased from 0.974 mA/W to 6.332 mA/W, accompanied by obvious red shift. • Faster response and recovery speed compared to pure ZnO film PD. • Discusses the impact of PbS QDs on the photoelectric properties of ZnO film more comprehensively and systematically. [ABSTRACT FROM AUTHOR]

Carbon (C) is a common impurity that acts as a compensator within GaN grown via metal–organic chemical vapor deposition (MOCVD). Reducing C in GaN will help reduce the compensation level and provide a route to achieve GaN with reliably low effective doping for high‐power device applications. GaN grown with fast growth rates on bulk GaN with various offcut angles via conventional‐MOCVD (C‐MOCVD) and laser‐assisted MOCVD (LA‐MOCVD) is compared and analyzed. C‐incorporation effects are compared through quantitative secondary‐ion mass spectroscopy analysis in GaN grown on GaN substrate with offcut angles of 4° and 0.3° toward m‐plane over a wide range of growth rates by C‐MOCVD and LA‐MOCVD. For both growth techniques investigated, a significant reduction in C‐incorporation is observed when a high‐offcut‐angle (4°) substrate is used as compared to a lower‐offcut‐angle (0.3°) substrate. With C‐MOCVD, at the fastest growth condition investigated (17.26 μm h−1 at 0.3°‐offcut, 15.25 μm h−1 at 4°‐offcut), a reduction in [C] by 21.2X is observed with an increase in the offcut angle from 0.3° to 4°. A 82.6X reduction in [C] is observed with the similar fast growth condition via LA‐MOCVD on GaN with 4° offcut angle (9.78 μm h−1) as compared to C‐MOCVD at 0.3° offcut angle (17.26 μm h−1). [ABSTRACT FROM AUTHOR]

In this Letter, the role of background carbon in metalorganic chemical vapor deposition (MOCVD) β-Ga2O3 growth using trimethylgallium (TMGa) as the Ga precursor was investigated. The quantitative C and H incorporations in MOCVD β-Ga2O3 thin films grown at different growth rates and temperatures were measured via quantitative secondary ion mass spectroscopy (SIMS). The SIMS results revealed both [C] and [H] increase as the TMGa molar flow rate/growth rate increases or growth temperature decreases. The intentional Si incorporation in MOCVD β-Ga2O3 thin films decreases as the growth rate increases or the growth temperature decreases. For films grown at relatively fast growth rates (GRs) (TMGa > 58 μmol/min, GR > 2.8 μm/h) or relatively low temperature (<950 °C), the [C] increases faster than that of the [H]. The experimental results from this study demonstrate the previously predicted theory—H can effectively passivate the compensation effect of C in n-type β-Ga2O3. The extracted net doping concentration from quantitative SIMS {[Si]-([C]-[H])} agrees well with the free carrier concentration measured from Hall measurement. The revealing of the role of C compensation in MOCVD β-Ga2O3 and the effect of H incorporation will provide guidance on designing material synthesis for targeted device applications. [ABSTRACT FROM AUTHOR]

Abstract: Hollow spheres with nanometer to micrometer dimensions have been of great interest in many areas of science and technology due to their special structure and properties such as large specific area, surface permeability and low density. In this work, hollow copper microspheres were employed as a catalyst to degrade dyes. The microspheres show good catalytic activities in degradation reactions of dyes and maintain their catalytic activity when reused multiple times. The reaction rate of eosin Y (EY) and methylene blue (MB) degradation was enhanced by 7.5–15 times by hollow copper microspheres compared with the control test. Copper is particularly attractive as a catalyst, since it is orders of magnitude cheaper than any noble metal; so the hollow copper microspheres are expected to play an important role in the fields of catalysis and environmental remediation. [Copyright &y& Elsevier]

Abstract: Current injection efficiency and its impact on efficiency-droop in InGaN single quantum well (QW) based light-emitting diodes (LEDs) are investigated. The analysis is based on current continuity relation for drift and diffusion carrier transport across the QW-barrier system. A self-consistent 6-band k · p method is used to calculate the band structure for InGaN QW. The analysis indicates that the internal quantum efficiency in the conventional 24-Å In0.28Ga0.72N–GaN QW structure reaches its peak at low injection current density and reduces gradually with further increase in current due to the large carrier thermionic emission. Structures combining 24-Å In0.28Ga0.72N QW with 15-Å Al0.1Ga0.9N barriers show slight reduction in quenching of the injection efficiency as current density increases. The use of 15-Å Al0.83In0.17N barriers shows significant reduction in efficiency-droop (10% reduction of the internal quantum efficiency at current density of 620A/cm2). Thus, InGaN QWs employing thin layers of larger bandgap AlInN barriers suppress the efficiency-droop phenomenon significantly. [Copyright &y& Elsevier]

Abstract: In this study, we report on the pulsed metalorganic vapor phase epitaxy (MOVPE) of InN as well as the optical and electronic properties of the films as a function of V/III ratio and growth temperatures. The growth of InN films was conducted utilizing a vertical reactor with TMIn and NH3 as the In- and N-precursors, respectively. Metallic droplet-free InN films were achieved on GaN/sapphire template in a pulsed MOVPE mode with low V/III ratio condition. In the pulsed growth mode, NH3 was constantly flowing while the TMIn was sent into the reactor chamber for a 36-s pulse and then it bypassed the reactor chamber for an 18-s pulse for a total cycle time of 54s. At a growth pressure of 200Torr, the effects of growth temperature (510–575°C) and V/III ratio (12,460–17,100) on the photoluminescence (PL) transitions were investigated. Morphological evolution as well as the electrical quality of the overgrown films have also been studied for the given growth conditions. [Copyright &y& Elsevier]

Abstract: Self-assembled InGaN quantum dots (QDs) have been grown using metalorganic vapor-phase epitaxy (MOVPE), without using anti-surfactant. Using 120s annealing, InGaN QDs have been successfully formed with a circular base diameter of 40nm and an average height of 4nm, with QDs density of 4×109 cm−2. The InGaN QDs have peak photoluminescence (PL) wavelengths of 519 and 509nm for samples without and with a GaN upper barrier, respectively. The full-width half-maximum (FWHM) of the PL spectra ranges from 56.6 up to 69.6nm. These results demonstrates that high In-content InGaN QDs can be grown by MOVPE, and can potentially be utilized as the active media for light-emitting diodes (LEDs) and semiconductor laser diodes for green emission. [Copyright &y& Elsevier]

GaN is rapidly gaining attention for implementation in power electronics but is still impacted by its high density of threading dislocations (TDs), which have been shown to facilitate current leakage through devices limiting their performance and reliability. Here, we discuss a novel implementation of photoluminescence (PL) imaging to study TDs in regions within vertically structured p-i-n GaN (PIN) diodes consisting of metalorganic chemical vapor deposition (MOCVD) epitaxial layers grown on ammonothermal GaN (am-GaN) substrates. PL imaging with a sub-bandgap excitation energy (3.1 eV) reveals TDs with excellent clarity in three dimensions within the am-GaN substrate. Galvanometric-driven PL imaging allows the microstructure of hundreds of devices to be characterized in a single session, enhancing the screening process through the addition of device specific TD location tracking and density mapping. The visibility, structural characteristics, luminescent nature and evolution of TDs through the GaN growth process are described, potentially providing the ability to define TD structures associated with leakage current. [ABSTRACT FROM AUTHOR]

The design of InGaN-delta-InN quantum wells (QWs) leads to significant redshift for nitride active region with large electron-hole wave function overlap (Γe_hh) and spontaneous emission rate. The analysis was carried out by using self-consistent six-band k·p band formalism. The design of active region consisting of 30 Å In0.25Ga0.75N QW with InN delta-layer leads to large Γe_hh of >50% with emission wavelength in the yellow and red spectral regimes, which is applicable for nitride-based light-emitting diodes. [ABSTRACT FROM AUTHOR]

We present a visible III-nitride gain medium based on type-II InGaN-GaNAs quantum well (QW), employing thin dilute-As (∼3%) GaNAs layer. The utilization of GaNAs layer shifts the hole confinement to the center of the type-II QW, which significantly reduces the charge separation effect. The optical gain and spontaneous recombination rate of the type-II InGaN-GaNAs QW are analyzed and compared with those of conventional InGaN QW emitting in the blue regime (λ∼450 nm), using six-band k.p formalism for energy dispersion of the III-nitride wurtzite semiconductor. The use of type-II QW leads to significant improvement in the optical gain and spontaneous recombination rate. [ABSTRACT FROM AUTHOR]

β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor with a bandgap energy of ∼ 4.8 eV and a predicted high critical electric field strength of ∼8 MV/cm, enabling promising applications in next generation high power electronics and deep ultraviolet optoelectronics. The advantages of Ga2O3 also stem from its availability of single crystal bulk native substrates synthesized from melt, and its well-controllable n-type doping from both bulk growth and thin film epitaxy. Among several thin film growth methods, metalorganic chemical vapor deposition (MOCVD) has been demonstrated as an enabling technology for developing high-quality epitaxy of Ga2O3 thin films, (AlxGa1−x)2O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2O3 thin films via different growth methods, with a focus on the growth of Ga2O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2O3 are discussed, along with the opportunities of future works to enhance the state-of-the-art device performance based on this emerging UWBG semiconductor material system. [ABSTRACT FROM AUTHOR]

This Letter reports a highly scaled 90 nm gate length β-Ga2O3 (Ga2O3) T-gate MOSFET with a power gain cutoff frequency (fMAX) of 55 GHz. The 60 nm thin epitaxial Ga2O3 channel layer was grown by molecular beam epitaxy, while the highly doped (n++) source/drain regions were regrown using metal organic chemical vapor deposition. Maximum on current (IDS,MAX) of 160 mA/mm and trans-conductance (gm) around 36 mS/mm were measured at VDS = 10 V for LSD = 1.5 μ m device. Transconductance and on current are limited by high channel sheet resistance (Rsheet). Gate/drain breakdown voltage of 125 V was measured for LGD = 1.2 μ m. We extracted 27 GHz current gain cutoff frequency (fT) and 55 GHz fMAX for 20 V drain bias for unpassivated devices. While no current collapse was seen initially for both drain and gate lag measurements for 500 ns pulse, moderate current collapse was observed after DC, RF measurements caused by electrical stressing. We calculated a high fT. VBR product of 3.375 THz V, which is comparable to the state-of-the-art GaN HEMTs. This figure of merit suggests that Ga2O3 could be a potential candidate for X-band application. [ABSTRACT FROM AUTHOR]

The impact of 1.8 MeV proton irradiation on metalorganic chemical vapor deposition grown (010) β -Ga2O3 Schottky diodes is presented. It is found that after a 10.8 × 10 13 cm − 2 proton fluence the Schottky barrier height of (1.40 ± 0.05 eV) and the ideality factor of (1.05 ± 0.05) are unaffected. Capacitance–voltage extracted net ionized doping curves indicate a carrier removal rate of 268 ± 10 cm − 1 . The defect states responsible for the observed carrier removal are studied through a combination of deep level transient and optical spectroscopies (DLTS/DLOS) as well as lighted capacitance–voltage (LCV) measurements. The dominating effect on the defect spectrum is due to the EC - 2.0 eV defect state observed in DLOS and LCV. This state accounts for ∼ 75 % of the total trap introduction rate and is the primary source of carrier removal from proton irradiation. Of the DLTS detected states, the EC - 0.72 eV state dominated but had a comparably smaller contribution to the trap introduction. These two traps have previously been correlated with acceptor-like gallium vacancy-related defects. Several other trap states at E C -0.36, E C -0.63, and E C -1.09 eV were newly detected after proton irradiation, and two pre-existing states at E C -1.2 and E C -4.4 eV showed a slight increase in concentration after irradiation, together accounting for the remainder of trap introduction. However, a pre-existing trap at EC - 0.40 eV was found to be insensitive to proton irradiation and, therefore, is likely of extrinsic origin. The comprehensive defect characterization of 1.8 MeV proton irradiation damage can aid the modeling and design for a range of radiation tolerant devices. [ABSTRACT FROM AUTHOR]

The in situ metalorganic chemical vapor deposition (MOCVD) growth of Al2O3 dielectrics on β-Ga2O3 and β-(AlxGa1−x)2O3 films is investigated as a function of crystal orientations and Al compositions of β-(AlxGa1−x)2O3 films. The interface and film qualities of Al2O3 dielectrics are evaluated by high-resolution x-ray diffraction and scanning transmission electron microscopy imaging, which indicate the growth of high-quality amorphous Al2O3 dielectrics with abrupt interfaces on (010), (100), and ( 2 ¯ 01) oriented β-(AlxGa1−x)2O3 films. The surface stoichiometries of Al2O3 deposited on all orientations of β-(AlxGa1−x)2O3 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) Al2O3 dielectrics. The evolution of band offsets at both in situ MOCVD and ex situ ALD deposited Al2O3/β-(AlxGa1−x)2O3 is determined as a function of Al composition, indicating the influence of the deposition method, orientation, and Al composition of β-(AlxGa1−x)2O3 films on resulting band alignments. Type II band alignments are determined at the MOCVD grown Al2O3/β-(AlxGa1−x)2O3 interfaces for the (010) and (100) orientations, whereas type I band alignments with relatively low conduction band offsets are observed along the ( 2 ¯ 01) orientation. The results from this study on MOCVD growth and band offsets of amorphous Al2O3 deposited on differently oriented β-Ga2O3 and β-(AlxGa1−x)2O3 films will potentially contribute to the design and fabrication of future high-performance β-Ga2O3 and β-(AlxGa1−x)2O3 based transistors using MOCVD in situ deposited Al2O3 as a gate dielectric. [ABSTRACT FROM AUTHOR]

In this work, the structural and electrical properties of metalorganic chemical vapor deposited Si-doped β-(AlxGa1−x)2O3 thin films grown on (010) β-Ga2O3 substrates are investigated as a function of Al composition. The room temperature Hall mobility of 101 cm2/V s and low temperature peak mobility (T = 65 K) of 1157 cm2/V s at carrier concentrations of 6.56 × 1017 and 2.30 × 1017 cm−3 are measured from 6% Al composition samples, respectively. The quantitative secondary ion mass spectroscopy (SIMS) characterization reveals a strong dependence of Si and other unintentional impurities, such as C, H, and Cl concentrations in β-(AlxGa1−x)2O3 thin films, with different Al compositions. Higher Al compositions in β-(AlxGa1−x)2O3 result in lower net carrier concentrations due to the reduction of Si incorporation efficiency and the increase of C and H impurity levels that act as compensating acceptors in β-(AlxGa1−x)2O3 films. Lowering the growth chamber pressure reduces Si concentrations in β-(AlxGa1−x)2O3 films due to the increase of Al compositions as evidenced by comprehensive SIMS and Hall characterizations. Due to the increase of lattice mismatch between the epifilm and substrate, higher Al compositions lead to cracking in β-(AlxGa1−x)2O3 films grown on β-Ga2O3 substrates. The (100) cleavage plane is identified as a major cracking plane limiting the growth of high-quality Si-doped (010) β-(AlxGa1−x)2O3 films beyond the critical thicknesses, which leads to highly anisotropic and inhomogeneous behaviors in terms of conductivity. [ABSTRACT FROM AUTHOR]

LiGa5O8, a recently discovered ultrawide bandgap semiconductor exhibiting p-type conductivity at room temperature, is grown on (010) β-Ga2O3 substrate. Utilizing a mist chemical vapor deposition method, LiGa5O8 thin film grown on insulating Ga2O3 substrate exhibits hole concentration ∼2.31 × 1018 cm−3 and hole mobility ∼2.07 cm2/V s. The resulting heterostructure is characterized comprehensively. A smooth, uniform film growth was observed by scanning electron microscopy and atomic force microscopy imaging. Cross-sectional scanning transmission electron microscopy and x-ray diffraction confirm the growth of spinel cubic crystal structure of LiGa5O8 along the [110] direction. Moreover, the valence and conduction band offsets at p-LiGa5O8/β-Ga2O3 heterointerface were determined via x-ray photoelectron spectroscopy. The determined band alignments at LiGa5O8/β-Ga2O3 interface reveal the formation of a type-II (staggered) heterojunction. The experimental measurements provide valuable parameters of the band offsets at the heterointerface, addressing a crucial aspect for future power electronic device design and fabrication based on β-Ga2O3 ultrawide bandgap semiconductors. [ABSTRACT FROM AUTHOR]

A complete set of all optical phonon modes predicted by symmetry for bixbyite structure indium oxide is reported here from a combination of far-infrared and infrared spectroscopic ellipsometry, as well as first principles calculations. Dielectric function spectra measured on high quality, marginally electrically conductive melt grown single bulk crystals are obtained on a wavelength-by-wavelength (also known as point-by-point) basis and by numerical reduction of a subtle free charge carrier Drude model contribution. A four-parameter semi-quantum model is applied to determine all 16 pairs of infrared-active transverse and longitudinal optical phonon modes, including the high-frequency dielectric constant, ε ∞ = 4.05 ± 0.05. The Lyddane–Sachs–Teller relation then gives access to the static dielectric constant, ε DC = 10.55 ± 0.07. All experimental results are in excellent agreement with our density functional theory calculations and with previously reported values, where existent. We also perform optical Hall effect measurements and determine for the unintentionally doped n -type sample a free electron density of n = (2.81 ± 0.01) × 10 17 cm − 3 , a mobility of μ = (112 ± 3) cm 2 /(Vs), and an effective mass parameter of (0.208 ± 0.006) m e. Density and mobility parameters compare very well with the results of electrical Hall effect measurements. Our effective mass parameter, which is measured independently of any other experimental technique, represents the bottom curvature of the Γ point in In 2 O 3 in agreement with previous extrapolations. We use terahertz spectroscopic ellipsometry to measure the quasi-static response of In 2 O 3 , and our model validates the static dielectric constant obtained from the Lyddane–Sachs–Teller relation. [ABSTRACT FROM AUTHOR]

Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 1017 cm−3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (EC − 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm2/V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices. [ABSTRACT FROM AUTHOR]

III-nitrides have revolutionized lighting technology and power electronics. Expanding the nitride semiconductor family to include heterovalent ternary nitrides opens up new and exciting opportunities for device design that may help overcome some of the limitations of the binary nitrides. However, the more complex cation sublattice also gives rise to new interactions with both native point defects and defect complexes that can introduce disorder on the cation sublattice. Here, depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy measurements of defect energy levels in ZnGeN2 combined with transmission electron microscopy and x-ray diffraction reveal optical signatures of mid-gap states that can be associated with cation sublattice disorder. The energies of these characteristic optical signatures in ZnGeN2 thin films grown by metal–organic chemical vapor deposition are in good agreement with multiple, closely spaced band-like defect levels predicted by density functional theory. We correlated spatially resolved optical and atomic composition measurements using spatially resolved x-ray photoelectron spectroscopy with systematically varied growth conditions on the same ZnGeN2 films. The resultant elemental maps vs defect spectral energies and intensities suggest that cation antisite complexes (ZnGe–GeZn) form preferentially vs isolated native point defects and introduce a mid-gap band of defect levels that dominate electron–hole pair recombination. Complexing of ZnGe and GeZn antisites manifests as disorder in the cation sub-lattice and leads to the formation of wurtzitic ZnGeN2 as indicated by transmission electron microscopy diffraction patterns and x-ray diffraction reciprocal space maps. These findings emphasize the importance of growth and processing conditions to control cation place exchange. [ABSTRACT FROM AUTHOR]

N-polar AlGaN is an emerging wide-bandgap semiconductor for next-generation high electron mobility transistors and ultraviolet light emitting diodes and lasers. Here, we demonstrate the growth and characterization of high-quality N-polar AlGaN films on C-face 4H-silicon carbide (SiC) substrates by molecular beam epitaxy. On optimization of the growth conditions, N-polar AlGaN films exhibit a crack free, atomically smooth surface (rms roughness ∼ 0.9 nm), and high crystal quality with low density of defects and dislocations. The N-polar crystallographic orientation of the epitaxially grown AlGaN film is unambiguously confirmed by wet chemical etching. We demonstrate precise compositional tunability of the N-polar AlGaN films over a wide range of Al content and a high internal quantum efficiency ∼74% for the 65% Al content AlGaN film at room temperature. Furthermore, controllable silicon (Si) doping in high Al content (65%) N-polar AlGaN films has been demonstrated with the highest mobility value ∼65 cm2/V-s observed corresponding to an electron concentration of 1.1 × 1017 cm−3, whereas a relatively high mobility value of 18 cm2/V-s is sustained for an electron concentration of 3.2 × 1019 cm−3, with an exceptionally low resistivity value of 0.009 Ω·cm. The polarity-controlled epitaxy of AlGaN on SiC presents a viable approach for achieving high-quality N-polar III-nitride semiconductors that can be harnessed for a wide range of emerging electronic and optoelectronic device applications. [ABSTRACT FROM AUTHOR]

Growths of monoclinic (AlxGa1−x)2O3 thin films up to 99% Al contents are demonstrated via metalorganic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa) as the Ga precursor. The utilization of TMGa, rather than triethylgallium, enables a significant improvement of the growth rates (>2.5 μm h−1) of β‐(AlxGa1−x)2O3 thin films on (010), (100), and (2¯01) β‐Ga2O3 substrates. By systematically tuning the precursor molar flow rates, growth of coherently strained phase pure β‐(AlxGa1−x)2O3 films is demonstrated by comprehensive material characterizations via high‐resolution X‐ray diffraction (XRD) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging. Monoclinic (AlxGa1−x)2O3 films with Al contents up to 99, 29, and 16% are achieved on (100), (010), and (2¯01) β‐Ga2O3 substrates, respectively. Beyond 29% of Al incorporation, the (010) (AlxGa1−x)2O3 films exhibit β‐ to γ‐phase segregation. β‐(AlxGa1−x)2O3 films grown on (2¯01) β‐Ga2O3 show local segregation of Al along (100) plane. Record‐high Al incorporations up to 99% in monoclinic (AlxGa1−x)2O3 grown on (100) Ga2O3 are confirmed from XRD, STEM, electron nanodiffraction, and X‐ray photoelectron spectroscopy measurements. These results indicate great promises of MOCVD development of β‐(AlxGa1−x)2O3 films and heterostructures with high Al content and growth rates using TMGa for next‐generation high‐power and high‐frequency electronic devices. [ABSTRACT FROM AUTHOR]

Devices based on gallium nitride (GaN) have great potential for high power switching applications due to the high breakdown field and high electron mobility. In this work, we present a vertical GaN-on-GaN PN power diode using high dielectric constant material, BaTiO3, for electrical field management and high breakdown voltages, in together with an optimized guard-ring and field plate design. Numerical simulation shows that with high-k dielectrics implemented, the peak electrical field at the PN interface is mitigated from 3.5 to 3.1 MV/cm under a reverse bias of −9.05 kV. The device design with BaTiO3 shows a breakdown voltage of 9.65 kV or about 600 V improvement. The fabricated diodes with a 57 μm thick drift layer demonstrate a breakdown voltage of 7.86 kV on a bulk GaN substrate. The device has an on-resistance of 2.8 mΩ cm 2 and a Baliga figure of merit of 22 GW/ cm 2 . [ABSTRACT FROM AUTHOR]

The lack of p-type doping has impeded the development of vertical gallium oxide (Ga2O3) devices. Current blocking layers (CBLs) using implanted deep acceptors have been used to demonstrate vertical devices. This paper presents a pioneering demonstration of in situ Mg-doped β-Ga2O3 CBLs grown using metal–organic chemical vapor deposition. The Mg-doping density during growth was calibrated by quantitative secondary ion mass spectroscopy. Electrical test structures were designed with in situ Mg doped layers with various targeted Mg doping concentrations. The effectiveness of the CBL is characterized by using temperature-dependent current–voltage measurements using n-Mg-doped-n structures, providing crucial insight into the underlying mechanisms. Pulsed measurements show similar blocking characteristics as DC. 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 an alternate perspective on the optimization of CBL performance. Breakdown measurements show a peak 4 MV/cm field strength. [ABSTRACT FROM AUTHOR]

A detailed study comparing defect incorporation between laser-assisted metal-organic chemical vapor deposition (MOCVD)-grown GaN and conventional low- and high-growth-rate MOCVD GaN was conducted. Using deep-level transient and optical spectroscopy, traps throughout the bandgap were characterized where traps were found at EC-0.25 eV, EC-0.57 eV, EC-0.72 eV, EC-0.9 eV, EC-1.35 eV, EC-2.6 eV, and EC-3.28 eV in all three samples. This indicates no new traps were observed in the laser-assisted MOCVD GaN sample. Overall, the trap concentrations in the laser-assisted MOCVD sample were ∼2× higher than the optimal low-growth-rate sample, but this is primarily due to the increase in gallium vacancy EC-2.6 eV and carbon-related EC-3.28 eV trap concentrations. The EC-0.9 eV trap concentration was ∼2× higher in the laser-assisted sample, so proton irradiation experiments were conducted to identify the physical source of this level. The results indicated this was a native point defect likely related to gallium interstitials. Overall, this study shows that the laser-assisted MOCVD growth method is promising for future thick, high-quality GaN epilayers after further growth optimizations. [ABSTRACT FROM AUTHOR]

This paper presents the effect of thermal annealing on β-Ga2O3 thin film solar-blind (SB) photodetector (PD) synthesized on c-plane sapphire substrates by a low pressure chemical vapor deposition (LPCVD). The thin films were synthesized using high purity gallium (Ga) and oxygen (O2) as source precursors. The annealing was performed ex situ the under the oxygen atmosphere, which helped to reduce oxygen or oxygen-related vacancies in the thin film. Metal/semiconductor/metal (MSM) type photodetectors were fabricated using both the as-grown and annealed films. The PDs fabricated on the annealed films had lower dark current, higher photoresponse and improved rejection ratio ( R250/ R370 and R250/ R405) compared to the ones fabricated on the as-grown films. These improved PD performances are due to the significant reduction of the photo-generated carriers trapped by oxygen or oxygen-related vacancies. [ABSTRACT FROM AUTHOR]

Understanding the thermal stability and degradation mechanism of β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2O3 FinFET grown on a native β-Ga2O3 substrate, fabricated by metal-assisted chemical etching with Al2O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion/Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into the stability and promise of β-Ga2O3 FinFETs compared to their planar counterparts. [ABSTRACT FROM AUTHOR]

Background: With the release of genomic data for B.rapa, B.oleracea, and B.napus, research on the genetic and molecular functions of Brassica spp. has entered a new stage. PEBP genes in plants play an important role in the transition to flowering as well as seed development and germination. Molecular evolutionary and functional analyses of the PEBP gene family in B.napus based on molecular biology methods can provide a theoretical basis for subsequent investigations of related regulators. Results: In this paper, we identified a total of 29 PEBP genes from B.napus that were located on 14 chromosomes and 3 random locations. Most members contained 4 exons and 3 introns; motif 1 and motif 2 were the characteristic motifs of PEBP members. On the basis of intraspecific and interspecific collinearity analyses, it is speculated that fragment replication and genomic replication are the main drivers of for the amplification and evolution of the PEBP gene in the B.napus genome. The results of promoter cis-elements prediction suggest that BnPEBP family genes are inducible promoters, which may directly or indirectly participate in multiple regulatory pathways of plant growth cycle. Furthermore, the tissue-specific expression results show that the expression levels of BnPEBP family genes in different tissues were quite different, but the gene expression organization and patterns of the same subgroup were basically the same. qRT‒PCR revealed certain spatiotemporal patterns in the expression of the PEBP subgroups in roots, stems, leaves, buds, and siliques, was tissue-specific, and related to function. Conclusions: A systematic comparative analysis of the B.napus PEBP gene family was carried out at here. The results of gene identification, phylogenetic tree construction, structural analysis, gene duplication analysis, prediction of promoter cis-elements and interacting proteins, and expression analysis provide a reference for exploring the molecular mechanisms of BnPEBP family genes in future research. [ABSTRACT FROM AUTHOR]

This Letter reports a high performance β -Ga2O3 thin channel MOSFET with T gate and degenerately doped (n++) source/drain contacts regrown by metal organic chemical vapor deposition. Highly scaled T-gate with a gate length of 160–200 nm was fabricated to achieve enhanced RF performance and passivated with 200 nm silicon nitride. Peak drain current (ID,MAX) of 285 mA/mm and peak transconductance (gm) of 52 mS/mm were measured at 10 V drain bias with 23.5 Ω mm on resistance (RON). Metal/n++ contact resistance of 0.078 Ω mm was extracted from transfer length measurements. RON is possibly dominated by interface resistance between channel and highly doped n++ regrown layer. A gate-to-drain breakdown voltage of 192 V is measured for LGD = 355 nm resulting in average breakdown field (EAVG) of 5.4 MV/cm. This EAVG is the highest reported among all sub-micron gate length lateral FETs. Current gain cut off frequency (fT) of 11 GHz and record power gain cut off frequency (fMAX) of approximately 48 GHz were extracted from small signal measurements. fT is limited by DC-RF dispersion due to interface traps which needs further investigation. The fT·VBR product is 2.112 THz V for 192 V breakdown voltage. Device surpasses the switching figure of merit of Silicon and competitive with mature wide bandgap devices. [ABSTRACT FROM AUTHOR]

In this study, the growth of unintentionally doped semiconductor indium oxide with ultrafast growth rates on c-plane sapphire by low pressure chemical vapor deposition (LPCVD) was demonstrated. The effect of key growth parameters, such as oxygen flow rate and distance between the substrate to the indium source, on the growth rate, crystalline quality, surface morphology, as well as carrier transport properties were studied. The growth rate is highly dependent on the oxygen flow rate and the distance between the indium source and the substrate: (i) the growth rate reaches 113 μm/h with an oxygen flow rate of 75 sccm under the investigated growth condition; and (ii) it decreases exponentially with the increase of distance between the indium source and the substrate. X-ray diffraction characterization of the as-grown films indicates that the increase of oxygen flow rate leads to the suppression of (100) facet formation, significantly influencing the film morphology. The LPCVD growth conditions also determine the background doping and carrier mobility. With an oxygen flow rate of 75 sccm, a high electron mobility of 126 cm2 V−1 s−1 with a bulk concentration of 3.9 × 1017 cm−3 was obtained. Results from this work provide guidance on LPCVD growth of In2O3 with targeted growth rate, surface morphology, carrier concentration, and mobility. [ABSTRACT FROM AUTHOR]

Background carbon (C) impurity incorporation in metalorganic chemical vapor deposition (MOCVD) grown gallium nitride (GaN) represents one of the major issues in further improving GaN vertical power device performance. This work presents a laser-assisted MOCVD (LA-MOCVD) technique to address the high-C issue in MOCVD homoepitaxial GaN under different growth rate (Rg) regimes and studies the correlations between [C] and Rg. [C] in LA-MOCVD GaN is reduced by 50%–90% as compared to the conventional MOCVD GaN for a wide growth rate range between 1 and 16 μm/h. A mass-transport based model is developed to understand the C incorporation at different Rg regimes. The results obtained from the developed model are in good agreement with experimental data. The model further reveals that LA-MOCVD effectively suppresses C incorporation by reducing the active C species in the gas phase. Moreover, high step velocity in step flow growth mode can facilitate C incorporation at fast Rg, exhibiting steeper C increase. The theoretical model indicates that [C] can be suppressed below 1016 cm−3 with a fast growth rate (Rg) of 10 μm/h by utilizing higher power LA-MOCVD and freestanding GaN substrates with larger off-cut angles. [ABSTRACT FROM AUTHOR]

High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼1015 cm−3) 28 μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB) of 4.9 kV and a low specific on-resistance (RON) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2B/RON) of 27 GW/cm2. [ABSTRACT FROM AUTHOR]

This paper presents the synthesis of wide bandgap Ga2O3 thin films on differently oriented sapphire substrates by using low pressure chemical vapor deposition (LPCVD) technique. The effects of substrate orientation on the Ga2O3 thin film surface morphology, crystal orientation, growth rate, and optical properties were studied. The Ga2O3 thin films were synthesized on the c-plane (0001), a-plane (11−20), and r-plane (1−102) sapphire substrates using high purity metallic Ga and oxygen (O2) as source materials and argon (Ar) as carrier gas. The Ga2O3 thin films grown on the c-plane and a-plane sapphire substrates are composed of pure β-Ga2O3. A mixture of β-Ga2O3 and α-Ga2O3 phases is observed for the films grown on r-plane sapphire substrate. Well-distinct transmission, absorption, and reflectance edge at Eg ∼ 4.6-4.7 eV are visible for all the films in the optical spectra measured in the spectral range from 200 to 800 nm. [ABSTRACT FROM AUTHOR]

In this paper, synthesis of indium nitride (InN) nanowires (NWs) by chemical vapor deposition (CVD) is studied. InN NWs were synthesized via a vapor–liquid–solid (VLS) growth mechanism using high purity indium foil and ammonia as the source materials, and nitrogen as carrier gas. The mixture of nonpolar m-plane oriented and polar c-plane oriented tapered InN NWs is observed grown on top of Si (100) substrate. Energy dispersive spectroscopy (EDS) showed that the tips of the NWs are primarily consisted of Au and the rest of the NWs are consisted of indium (In) and nitrogen (N). High resolution scanning electron microscopy (HRSEM) revealed that the InN NWs have both triangular and hexagonal cross sections. Transmission electron microscopy (TEM) diffraction pattern showed that the NWs are high quality single crystals having wurtzite crystal structure. High resolution transmission electron microscopy (HRTEM) showed the growth directions of the InN NWs with triangular cross section are along 〈10−10〉 nonpolar m-plane orientation and the InN NWs with hexagonal cross section are along 〈0001〉 polar c-plane orientation. [ABSTRACT FROM AUTHOR]

Coincidentally, our group just developed terahertz quantum cascade lasers (THz QCLs) based on resonant phonon scheme, and that APL paper[1] was my natural choice for the centennial book. We decided to celebrate the APL 60th birthday, in print, by inviting our editors to reflect on their experience as editors and APL authors. 82, 1015 (2003).10.1063/1.1554479 2 B. S. Williams, S. Kumar, H. Callebaut, Q. Hu, and J. L. Reno, " Terahertz quantum cascade laser at 100 m using metal waveguide for mode confinement", Appl. Phys. Deputy Editor, David Long Price APL's 60th Anniversary gives me the occasion to reflect on its 50th Anniversary, when I also had the privilege to be a member of APL's editorial team and to realize what a difference 10 years makes. [Extracted from the article]

In this work, β-Ga2O3 fin field-effect transistors (FinFETs) with metalorganic chemical vapor deposition grown epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are demonstrated. β-Ga2O3 fin channels with smooth sidewalls are produced by the plasma-free metal-assisted chemical etching (MacEtch) method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages is also characterized. The FinFET with channel perpendicular to the [102] direction is found to exhibit the lowest subthreshold swing and hysteresis. [ABSTRACT FROM AUTHOR]

Summary: Depending on a biofilm lifestyle, Streptococcus mutans (S. mutans) is thought to be one of the primary causative agents of dental caries. Biofilm formation and adhesion are crucial physiological functions and virulence factors for S. mutans. Thus, attempts to control the development of dental caries only by inhibiting one of the several virulence factors are not effective. Cyclic diguanylate (c-di-GMP) [bis(3′,5′)-cyclic diguanylic acid] is a prokaryotic cyclic dinucleotide second messenger that has been implicated in determining the timing and amplitude of complex biological processes from biofilm formation and virulence to photosynthesis. Here, we demonstrate that this signaling molecule also plays a role in the ability of S. mutans to initiate biofilm formation and adhere to tooth surfaces. To test this hypothesis, S. mutans UA159 and its gcp gene knockout mutant were assayed for their ability to initiate biofilm formation and adherence. The spatial distribution and architecture of the biofilms were examined by scanning electron microscopy. These results show that inactivation of the gcp gene resulted in the formation of an abnormal biofilm. We confirmed that c-di-GMP was effective in preventing biofilm formation of S. mutans UA159. We also found that extracellular c-di-GMP inhibited the adherence of S. mutans to tooth surfaces and reduced (>50%) biofilm formation compared to the untreated control. These results indicate that c-di-GMP attenuates the caries-inducing virulence factors of S. mutans. This suggests that c-di-GMP may be used alone or in combination with other antimicrobial agents, and that such a treatment could be developed into a novel method to prevent tooth decay. [Copyright &y& Elsevier]

Herein, vertical GaN p–n diodes grown by metal organic chemical vapor deposition on hydride vapor epitaxy bulk GaN substrates are reported. The devices exhibit an ideality factor of 1.15, a turn‐on voltage of 3.2 V at 100 A cm−2, over 1 kV breakdown voltage, and specific on‐state resistance of 0.47 mΩ cm2, leading to a Baliga's figure of merit of ≈2.2 GW cm−2. The low specific on‐resistance, low turn‐on voltage, and the near‐unity ideality factor demonstrated here are attributed to the high epitaxial material quality and optimized low anode contact resistance. [ABSTRACT FROM AUTHOR]

High crystalline quality thick β-Ga2O3 drift layers are essential for multi-kV vertical power devices. Low-pressure chemical vapor deposition (LPCVD) is suitable for achieving high growth rates. This paper presents a systematic study of the Schottky barrier diodes fabricated on four different Si-doped homoepitaxial β-Ga2O3 thin films grown on Sn-doped (010) and (001) β-Ga2O3 substrates by LPCVD with a fast growth rate varying from 13 to 21 μm/h. A higher temperature growth results in the highest reported growth rate to date. Room temperature current density–voltage data for different Schottky diodes are presented, and diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage are studied. Temperature dependence (25–250 °C) of the ideality factor, barrier height, and specific on-resistance is also analyzed from the J–V–T characteristics of the fabricated Schottky diodes. [ABSTRACT FROM AUTHOR]

A method was developed for ketone synthesis via a photoredox‐assisted reductive acyl cross‐coupling (PARAC) using a nickel/photoredox dual‐catalyzed cross‐electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°‐alkyl 2‐pyridyl esters can act as acyl electrophiles while N‐(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°‐radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°‐3°, 3°‐2°, and aryl‐3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni0/NiI/NiIII pathway for ketone formation. [ABSTRACT FROM AUTHOR]

A method was developed for ketone synthesis via a photoredox‐assisted reductive acyl cross‐coupling (PARAC) using a nickel/photoredox dual‐catalyzed cross‐electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°‐alkyl 2‐pyridyl esters can act as acyl electrophiles while N‐(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°‐radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°‐3°, 3°‐2°, and aryl‐3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni0/NiI/NiIII pathway for ketone formation. [ABSTRACT FROM AUTHOR]

In situ etching using Ga flux in an ultra-high vacuum environment like molecular beam epitaxy is introduced as a method to make high aspect ratio three-dimensional (3D) structures in β -Ga2O3. Etching of β -Ga2O3 due to excess Ga adatoms on the epilayer surface had been viewed as non-ideal for epitaxial growth especially since it results in plateauing and lowering of the growth rate. In this study, we use this well-known reaction from epitaxial growth to intentionally etch β -Ga2O3. We demonstrate etch rate ranging from 2.9 to 30 nm/min with the highest reported etch rate being only limited by the highest Ga flux used. Patterned in situ etching is also demonstrated and used to study the effect of fin orientation on the sidewall profiles and dopant (Si) segregation on the etched surface. Using in situ Ga etching, we also demonstrate 150 nm wide fins and 200 nm wide nanopillars with high aspect ratio. This etching method could enable future development of highly scaled vertical and lateral 3D devices in β -Ga2O3. [ABSTRACT FROM AUTHOR]

A predicted type-II staggered band alignment with an approximately 1.4 eV valence band offset at the ZnGeN2/GaN heterointerface has inspired novel band-engineered III-N/ZnGeN2 heterostructure-based device designs for applications in high performance optoelectronics. We report on the determination of the valence band offset between metalorganic chemical vapor deposition grown (ZnGe)1−xGa2xN2, for x = 0 and 0.06, and GaN using x-ray photoemission spectroscopy. The valence band of ZnGeN2 was found to lie 1.45–1.65 eV above that of GaN. This result agrees well with the value predicted by first-principles density functional theory calculations using the local density approximation for the potential profile and quasiparticle self-consistent GW calculations of the band edge states relative to the potential. For (ZnGe)0.94Ga0.12N2 the value was determined to be 1.29 eV, ∼10%–20% lower than that of ZnGeN2. The experimental determination of the large band offset between ZnGeN2 and GaN provides promising alternative solutions to address challenges faced with pure III-nitride-based structures and devices. [ABSTRACT FROM AUTHOR]