A novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology.

In this study, a novel AlGaN/GaN heterostructure field-effect transistor based on open-gate technology was fabricated. Sample transistors of different structures and sizes were constructed. Through measurements, it was found that by changing the width of the opening, the threshold voltage of the device could be easily modulated across a larger range. The open-gate device had two working modes with different transconductance. When the gate-source voltage VGS ≤ - 4.5 V, only the open region was conductive, and a new working mechanism modulated the channel current. Corresponding theoretical analysis and calculations showed that its saturation mechanism was related to a virtual gate formed by electron injection onto the surface. Also, the gate-source voltage modulated the open channel current by changing the channel electron mobility through polarization Coulomb field scattering. When used as class-A voltage amplifiers, open-gate devices can achieve effective voltage amplification with very low power consumption.

Association between CFH single nucleotide polymorphisms and response to photodynamic therapy in patients with central serous chorioretinopathy.

PURPOSE: To evaluate the association between single nucleotide polymorphisms (SNPs) in the complement factor H (CFH) gene and response to PDT in patients with CSC. METHODS: 103 eyes from 93 patients with CSC were enrolled from Department of Ophthalmology of the People's Hospital Peking University. Genotyping for selected SNPs in the CFH gene was performed, and multivariate linear analysis was used to identify factors influencing PDT treatment outcomes. Genetics associations between SNPs in the CFH gene and response to PDT in patients with CSC were analyzed. RESULTS: None of the seven SNPs examined in this study (rs800292, rs1061170, rs3753394, rs3753396, rs2284664, rs1329428, and rs1065489) showed significant associations with 1-month outcomes after PDT in patients with CSC (P > 0.05). Baseline BCVA changed at 1 month after PDT (P < 0.001), and baseline retinal thickness was associated with changes in retinal thickness at 1 month after PDT (P < 0.001). Age was significantly associated with resolution of SRF at 1 month after PDT (P = 0.004). CONCLUSIONS: There were no significant associations between SNPs in the CFH gene and 1-month outcomes after PDT in patients with CSC. However, baseline BCVA, baseline retinal thickness, and age were significantly associated with response to PDT in patients with CSC. Larger studies with more power are necessary to further determine whether an association exists between SNPs in the CFH gene and PDT in patients with CSC.

Effect of a novel Ca-Si composite mineral on Cd bioavailability, transport and accumulation in paddy soil-rice system.

Ubiquitous cadmium (Cd) contamination in mine impacted paddy soil has been jeopardizing regional rice quality, which represents a dominant pathway of Cd exposure in populations depending on a rice diet. Two major aspects of mitigation, soil liming and Si fertilization, were integrated and investigated with a Ca-Si-rich composite mineral (CS) derived from feldspar and carbonate. With the CS amendment, bioavailable Cd in rice rhizosphere was reduced by 92-100% from tillering to maturation stage, paralleled by a marked increase in Cd bound to Fe/Mn oxides and carbonate. As indicated by XRD analysis, the much reduced labile pool of Cd in the CS-amended soil could be mainly attributed to Cd (co)precipitation (Cd(OH)2, Cd2(OH)3Cl, CH6Br3CdN) and surface complexation on more negatively charged oxides at elevated soil pH with CS addition. EDX line scan illustrated much more intensified Si deposition along root cross-section in the CS treatment, which resulted in 1.5-2.1-fold higher Cd sequestration in the CS-amended root than control. As a direct result, the root-to-shoots Cd translocation was reduced significantly by 42-51%, while a slightly less significant decrease in brown rice Cd was obtained with the CS treatment relative to control. The CS amendment showed differing effects on brown rice mineral accumulation, with 1.2-1.5-fold increase in brown rice Zn and simultaneously reduced Fe, Mn, Mg and Cu in brown rice. Our results call the readers' attention to the potential impact of soil ameliorator on grain mineral uptake, and we suggest that proper fortification with mineral fertilizers should be supplemented to assist sustainable rice production with improved mineral nutrition.

Nitrate reduced arsenic redox transformation and transfer in flooded paddy soil-rice system.

Inhibition of reductive transformation of arsenic (As) in flooded paddy soils is of fundamental importance for mitigating As transfer into food chain. Anaerobic arsenite (As(III)) oxidizers maintain As in less mobile fraction under nitrate-reducing conditions. In this study, we explored the dynamic profile of As speciation in porewater and As distribution among the pools of differential bioavailability in soil solid phase with and without nitrate treatment. In parallel, the abundance and diversity of As(III) oxidase gene (aioA) in flooded paddy soil with nitrate amendment was examined by quantitative PCR and aioA gene clone library. Furthermore, the impact of nitrate on As accumulation and speciation in rice seedlings was unraveled. With nitrate addition (25 mmol NO3- kg-1 soil), porewater As(III) was maintained at a consistently negligible concentration in the flooded paddy soil and the reductive dissolution of As-bearing Fe oxides/hydroxides was significantly restrained. Specifically, nitrate amendment kept 81% of total soil As in the nonlabile fraction with arsenate (As(V)) dominating after 30 days of flooding, compared to only 61% in the unamended control. Nitrate treatment induced 4-fold higher abundance of aioA gene, which belonged to domains of bacteria and archaea under the classes α-Proteobacteria (6%), ß-Proteobacteria (90%), É£-Proteobacteria (2%), and Thermoprotei (2%). By nitrate addition, As accumulation in rice seedlings was decreased by 85% with simultaneously elevated As(V) ratio in rice plant relative to control after 22 days of growth under flooded conditions. These results highlight that nitrate application can serve an efficient method to inhibit reductive dissolution of As in flooded paddy soils, and hence diminish As uptake by rice under anaerobic growing conditions.

Effect of Polarization Coulomb Field Scattering on Electrical Properties of the 70-nm Gate-Length AlGaN/GaN HEMTs.

This research presents the first experimental observation of the enhancement of the polarization Coulomb field (PCF) scattering by aggressive lateral scaling of GaN HEMTs. By decreasing the source-drain distance to 300 nm through n+-GaN ohmic regrowth, 70-nm gate AlGaN/GaN HEMTs achieved an extremely low electron mobility. Different from the electron mobility of the traditional device, which was determined by polar optical phonon scattering, the electron mobility of the 70-nm gate AlGaN/GaN HEMTs was dominated by PCF scattering due to the enhanced nonuniform strain distribution of the AlGaN barrier layer. Furthermore, compared with the parasitic access resistance at gate-source voltage VGS = 0 V, the parasitic access resistance at VGS = -2.5 V showed an increase of approximately 700%, which was also responsible for the enhanced PCF scattering.

Effect of Different Gate Lengths on Polarization Coulomb Field Scattering Potential in AlGaN/GaN Heterostructure Field-Effect Transistors.

The AlGaN/GaN heterostructure field-effect transistors with different gate lengths were fabricated. Based on the chosen of the Hamiltonian of the system and the additional polarization charges, two methods to calculate PCF scattering by the scattering theory were presented. By comparing the measured and calculated source-drain resistances, the effect of the different gate lengths on the PCF scattering potential was confirmed.

Improved Linearity with Polarization Coulomb Field Scattering in AlGaN/GaN Heterostructure Field-Effect Transistors.

The single-tone power of the AlGaN/GaN heterostructure field-effect transistors (HFETs) with different gate widths was measured. A distinct improvement in device linearity was observed in the sample with a larger gate width. The analysis of the variation of the parasitic source access resistance showed that, as the gate bias is increased, the polarization Coulomb field scattering can offset the increased polar optical phonon scattering and improve the device linearity. This approach is shown to be effective in improving the device linearity of AlGaN/GaN HFETs.

Growth of Large-Size SnS Thin Crystals Driven by Oriented Attachment and Applications to Gas Sensors and Photodetectors.

Freestanding large-size SnS thin crystals are synthesized via two-dimensional oriented attachment (OA) growth of colloidal quantum dots (CQDs) in a novel high-pressure solvothermal reaction. The SnS thin crystals present a uniform rectangular shape with a lateral size of 20-30 um and thickness of <10 nm. The evolution process demonstrates that a synergetic effect of pressure, aging time and organic ligands results in polycrystal-to-monocrystal formation and defect annihilation. Furthermore, gas sensor and photodetector devices, based on SnS thin single crystals, are also prepared. The sensing devices present high sensitivity, superior selectivity, low detection limit (≪100 ppb) and reversibility to NO2 at room temperature. The fabricated photodetector devices exhibit a high responsivity of 2.04 × 10(3) A W(1-) and high external quantum efficiency of ∼4.75 × 10(5) % at 532 nm, which are much higher than most of the photodetector devices.

Large rectification magnetoresistance in nonmagnetic Al/Ge/Al heterojunctions.

Magnetoresistance and rectification are two fundamental physical properties of heterojunctions and respectively have wide applications in spintronics devices. Being different from the well known various magnetoresistance effects, here we report a brand new large magnetoresistance that can be regarded as rectification magnetoresistance: the application of a pure small sinusoidal alternating-current to the nonmagnetic Al/Ge Schottky heterojunctions can generate a significant direct-current voltage, and this rectification voltage strongly varies with the external magnetic field. We find that the rectification magnetoresistance in Al/Ge Schottky heterojunctions is as large as 250% at room temperature, which is greatly enhanced as compared with the conventional magnetoresistance of 70%. The findings of rectification magnetoresistance open the way to the new nonmagnetic Ge-based spintronics devices of large rectification magnetoresistance at ambient temperature under the alternating-current due to the simultaneous implementation of the rectification and magnetoresistance in the same devices.

Influence of the ratio of gate length to drain-to-source distance on the electron mobility in AlGaN/AlN/GaN heterostructure field-effect transistors.

Using measured capacitance-voltage curves with different gate lengths and current-voltage characteristics at low drain-to-source voltage for the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) of different drain-to-source distances, we found that the dominant scattering mechanism in AlGaN/AlN/GaN HFETs is determined by the ratio of gate length to drain-to-source distance. For devices with small ratio (here, less than 1/2), polarization Coulomb field scattering dominates electron mobility. However, for devices with large ratio (here, more than 1/2), longitudinal optical (LO) phonon scattering and interface roughness scattering are dominant. The reason is closely related to polarization Coulomb field scattering.

Porous copper zinc tin sulfide thin film as photocathode for double junction photoelectrochemical solar cells.

Porous copper zinc tin sulfide (CZTS) thin film was prepared via a solvothermal approach. Compared with conventional dye-sensitized solar cells (DSSCs), double junction photoelectrochemical cells using dye-sensitized n-type TiO(2) (DS-TiO(2)) as the photoanode and porous p-type CZTS film as the photocathode shows an increased short circuit current, external quantum efficiency and power conversion efficiency.

Band-gap tunable (Cu2Sn)(x/3)Zn(1-x)S nanoparticles for solar cells.

Sphalerite-type (Cu(2)Sn)(x/3)Zn(1-x)S (0 < or = x < or = 0.75) nanocrystals with tunable band gaps were successfully prepared via a solvothermal approach. Band gaps of the nanoparticles could be adjusted from 3.48 eV to 1.23 eV by changing the composition. Their implementation in quantum dot sensitized solar cells (QDSSCs) suggests considerable potential in solar cells.