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In order to improve the feasibility, security and efficiency, this paper proposed a quantum key distribution protocol based on Bell states and its entanglement by establishing the classical channel and quantum channel between the two parties of communication. The protocol is feasibility, safe, simple and efficient. And it proves that the eavesdropper cannot obtain the secret key without being found through the rigorous mathematical derivations. It also got the mathematical model of efficiency and security, and analysed their relationship by MATLAB emulation. [ABSTRACT FROM AUTHOR]

An Ni/Au Schottky contact on an AlGaN/GaN heterostructure has been prepared. By using the peak-conductance model, the threshold voltage and the series resistance of the AlGaN/GaN diode are simultaneously extracted from the conductance--voltage (G-V) curve and found to be in good agreement with the ones obtained by using the capacitance--voltage (C-V) curve integration and the plot of dV/d(ln I) versus current I. Thus, a method of directly and simultaneously extracting both the threshold voltage and the series resistance from the conductance--voltage curve for the AlGaN/GaN Schottky diode is developed. [ABSTRACT FROM AUTHOR]

Using measured capacitance--voltage curves and current--voltage characteristics for the AlGaN/AlN/GaN heterostructure field-effect transistors with different gate lengths and drain-to-source distances, the influence of drain bias on the electron mobility is investigated. It is found that below the knee voltage the longitudinal optical (LO) phonon scattering and interface roughness scattering are dominant for the sample with a large ratio of gate length to drain-to-source distance (here 4/5), and the polarization Coulomb field scattering is dominant for the sample with a small ratio (here 1/5). However, the above polarization Coulomb field scattering is weakened in the sample with a small drain-to-source distance (here 20 µm) compared with the one with a large distance (here 100 µm). This is due to the induced strain in the AlGaN layer caused by the drain bias. [ABSTRACT FROM AUTHOR]

In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field (PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility. Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness. This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect. [ABSTRACT FROM AUTHOR]

Ti/Al based Ohmic contacts to as-grown N-polar GaN are investigated by cross-section transmission electron microscopy and energy dispersive x-ray spectroscopy. Due to the higher oxygen background doping in the N-polar GaN, the Al metal in Ohmic stacks is found to react with background oxygen more easily, resulting in more AlOx. In addition, the formation of AlOx is affected by the Al layer thickness greatly. The AlOx combined with the presence of AlN is detrimental to the Ohmic contacts for N-polar GaN compared with Ga-polar GaN. With the reduction of the Al layer thickness to some extent, less AlOx and AlN are formed, and lower Ohmic contact resistance is obtained. The lowest contact resistivity ρ of 1.97 × 10−6 Ω·cm2 is achieved with the Al layer thickness of 80 nm. [ABSTRACT FROM AUTHOR]

In this paper, two-dimensional (2D) transient simulations of an AlGaN/GaN high-electron-mobility transistor (HEMT) are carried out and analyzed to investigate the current collapse due to trapping effects. The coupling effect of the trapping and thermal effects are taken into account in our simulation. The turn-on pulse gate-lag transient responses with different quiescent biases are obtained, and the pulsed current–voltage (I–V) curves are extracted from the transients. The experimental results of both gate-lag transient current and pulsed I–V curves are reproduced by the simulation, and the current collapse due to the trapping effect is explained from the view of physics based on the simulation results. In addition, the results show that bulk acceptor traps can influence the gate-lag transient characteristics of AlGaN/GaN HEMTs besides surface traps and that the thermal effect can accelerate the emission of captured electrons for traps. Pulse transient simulation is meaningful in analyzing the mechanism of dynamic current collapse, and the work in this paper will benefit the reliability study and model development of GaN-based devices. [ABSTRACT FROM AUTHOR]

An unexpected "twinkling" appearance of partially covered chemical vapor deposition-grown graphene on the Cu substrate, showing strong grain orientation-dependent contrast of graphene—brighter, darker, or even invisible against the oxidized substrate—was observed with a scanning electron microscope. The intricate interplay between the electron channeling contrast, oxidation layer, and the imaging parameters was discussed. Imaging conditions affording stronger mass-thickness contrast was proposed to lessen the twinkling effect and thus enable unambiguous discrimination of graphene from the substrate. The findings reported here will have important implications for the reliable characterization of graphene and other 2D materials as well as the growth mechanism study of graphene. [ABSTRACT FROM AUTHOR]

High fidelity quantum operation of qubits plays an important role in realistic quantum sensing. It becomes more challenging when there are inevitable interactions between qubits in the solid system. We employ a composite pulse sequence to deal with the problems. The electron spin state of the nitrogen-vacancy center in diamond is flipped with high fidelity by the composite pulse at room temperature. In contrast with traditional rectangular pulses, the composite pulse has a wider excitation profile at the same Rabi frequency. Hence, the three sublevels of host nitrogen nuclear spin can be flipped efficiently and simultaneously, which enhances the signal contrast and detection sensitivity of quantum sensing universally. The enhancement effect works over a wide range of bias magnetic fields. Our scheme can be used for sensing temperature, strain, and electric field and can be applied to other spin–spin coupling systems. [ABSTRACT FROM AUTHOR]

Multiple spectrograms WVD needs to estimate noise variance for calculating auto-term support region, ad the weak signal will be overwhelmed by the strong signal. To solve this problem, the proposed method determined the threshold of support region by the dual tone dynamic range of the signal, and revised the amplitude of support region, which not only avoided noise variance estimation but also improved the signal's time-frequency concentration. Simulation results show that the proposed method reduces the interring cross-terms and preserves the details of weak signal. Finally the algorithm is achieved based on compute unified device architecture (CUDA) and the speedup can reach 50 times. [ABSTRACT FROM AUTHOR]

Nectarine (Prunus persica var. nectarina) is a sub-tropical fruit tree with strong cold sensitivity. In this study, flesh of nectarine (Shuguang) was used to determine the difference in transcriptional data before and after chilling injury under storage. In addition, genes responses involved in nectarine acclimation to cold stress were also explored. Results of the current study showed that nectarine was found to be more susceptible to chilling injury during storage at 5°C than at 0°C, and differentially expressed genes (DEGs) were concentrated in the late stage of low-temperature storage where chilling injury symptoms appeared at the end of the experiment. The key genes related to low-temperature response were associated with post-harvest biological processes. DEGs were annotated on the metabolic pathways of cold regulation signal transduction, cold resistance physiological metabolism and cold resistance-related protein synthesis. Moreover, the expression of genes related to cold stress such as plant hormone signal transduction element such as Auxin-responsive protein, transcription factors responding to cold stress such as WRKY transcription factor and genes related to maintaining membrane stability and regulating physiological metabolism such as proline dehydrogenase was more pronounced when nectarine was stored at 5°C than at 0°C. Overall, these findings showed that alteration in chilling temperature has substantial impact on the transcription levels associated with cold resistance pathway during the low-temperature storage of nectarine and thus promotes chilling injury disorders in nectarine. [ABSTRACT FROM AUTHOR]

AlGaN/GaN high-electron-mobility transistors (HEMTs) with postpassivation plasma treatment are demonstrated and investigated for the first time. The results show that postpassivation plasma treatment can reduce the gate leakage and enhance the drain current. Comparing with the conventional devices, the gate leakage of AlGaN/GaN HEMTs with postpassivation plasma decreases greatly while the drain current increases. Capacitance–voltage measurement and frequency-dependent conductance method are used to study the surface and interface traps. The mechanism analysis indicates that the surface traps in the access region can be reduced by postpassivation plasma treatment and thus suppress the effect of virtual gate, which can explain the improvement of DC characteristics of devices. Moreover, the density and time constant of interface traps under the gate are extracted and analyzed. [ABSTRACT FROM AUTHOR]

The Tayuan (Cu-Mo)-Pb-Zn deposit is located in the northern part of Daxinganling, NE China. Lenticular ore body occurs in the skarn zone. The skarn minerals mainly include garnet, pyroxene, epidote and wollastonite. Electron microprobe analysis shows that the end member of garnet is mainly andradite (AdGr), the pyroxene is mainly diopside, and epidote is mainly clinozoisite. These characteristics indicate that the Tayuan polymetallic skarn deposit is mainly calcareous skarn. Sometimes the content zonation can be observed in garnets. With one garnet crystal, content is shifty from the core to the rim. In general, the iron content in the core is higher than in the edge. The content in the garnet shows that the garnet in the Tayuan deposit formed from weak oxidation in alkaline environment with the oxygen fugacity increasing, suggesting that the hydrothermal fluid evolved from an acidic to a slight alkaline state. In the Tayuan polymetallic deposit, the ratio of Mn/Fe in pyroxene is about 1.3, and of Mg/Fe, it is about 2. The components of garnet in the Tayuan deposit plot in the field of the typical skarn Zn, Cu, Mo deposits in the world. [ABSTRACT FROM AUTHOR]

The electron mobility of the AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with the ratio of the gate length to the drain-to-source distance being less than 1/2 has been studied in the temperature range 100 300 K. The measured electron mobility at each testing temperature is obtained by using the capacitance-voltage ( C- V) and current-voltage ( I- V) characteristics measured at the corresponding temperature, and the theoretically calculated temperature-dependent electron mobility is determined by Matthiessen's law, which includes five kinds of important scattering mechanisms. For the prepared sample, the measured electron mobility with respect to the two-dimensional electron gas (2DEG) density was observed to increase to a peak point first and then decrease at each testing temperature. By comparing the measured electron mobility with the theoretically calculated value, the changing trend of the electron mobility at each testing temperature was found to be mainly determined by polarization Coulomb field (PCF) scattering. Particularly at lower temperature, PCF scattering plays a more significant role in the changing trend of the electron mobility. [ABSTRACT FROM AUTHOR]

High quality diamond epitaxial layers are prepared on polycrystalline and single-crystal diamonds by MPCVD. Field-effect transistors with gate length of 1 μm are fabricated by self-aligned process on them. The surface p -type channel of the diamond films were obtained by microwave hydrogen plasma treatment. The DC and RF characteristics of the field-effect transistors are compared. The polycrystalline diamond FETs show better DC and small-signal performance. Single-crystal diamond FETs show higher breakdown voltage and output power density due to its high crystal quality. The maximum output power density reaches 320 mW/mm and 450 mW/mm@1GHz for the polycrystalline diamond and single crystal diamond transistors, respectively. [ABSTRACT FROM AUTHOR]

We report on the temperature-dependent dc performance of AlGaN/GaN polarization doped field effect transistors (PolFETs). The rough decrements of drain current and transconductance with the operation temperature are observed. Compared with the conventional HFETs, the drain current drop of the PolFET is smaller. The transconductance drop of PolFETs at different gate biases shows different temperature dependences. From the aspect of the unique carrier behaviors of graded AlGaN/GaN heterostructure, we propose a quasi-multi-channel model to investigate the physics behind the temperature-dependent performance of AlGaN/GaN PolFETs. [ABSTRACT FROM AUTHOR]

The effect of an initially grown high-temperature AlN buffer (HT-AlN) layer's thickness on the quality of an AlN epilayer grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD) in a two-step growth process is investigated. The characteristics of AlN epilayers are analyzed by using triple-axis crystal X-ray diffraction (XRD) and atomic force microscopy (AFM). It is shown that the crystal quality of the AlN epilayer is closely related to its correlation length. The correlation length is determined by the thickness of the initially grown HT-AlN buffer layer. We find that the optimal HT-AlN buffer thickness for obtaining a high-quality AlN epilayer grown on sapphire substrate is about 20 nm. [ABSTRACT FROM AUTHOR]

Wafer-scale graphene field-effect transistors are fabricated using benzocyclobutene and atomic layer deposition Al2O3 as the top-gate dielectric. The epitaxial-graphene layer is formed by graphitization of a 2-inch-diameter Si-face semi-insulating 6H-SiC substrate. The graphene on the silicon carbide substrate is heavily n-doped and current saturation is not found. For the intrinsic characteristic of this particular channel material, the devices cannot be switched off. The cut-off frequencies of these graphene field-effect transistors, which have a gate length of 1 μm, are larger than 800 MHz. The largest one can reach 1.24 GHz. There are greater than 95% active devices that can be successfully applied. We thus succeed in fabricating wafer-scale gigahertz graphene field-effect transistors, which paves the way for high-performance graphene devices and circuits. [ABSTRACT FROM AUTHOR]

In this work, metal–insulator–semiconductor field effect transistors (MISFET) with gate length of 350 nm were fabricated on hydrogen‐terminated polycrystalline diamond by a self‐aligned process. Aluminium film with thickness of 2 nm was evaporated on the sample and formed self‐oxidised alumina to act as the gate dielectric. The devices show good direct current and radio frequency performances with a maximum frequency of oscillation (fmax) of 34 GHz and continuous‐wave output power density of 650 mW/mm at 10 GHz. [ABSTRACT FROM AUTHOR]

The valence band offset (VBO) of an Al0.17Ga0.83N/GaN heterojunction is determined to be 0.13 ± 0.07 eV by x-ray photoelectron spectroscopy. From the obtained VBO value, the conduction band offset (CBO) of ~0.22 eV is obtained. The results indicate that the Al0.17Ga0.83N/GaN heterojunction exhibits a type-I band alignment. [ABSTRACT FROM AUTHOR]

Excitation power and temperature-dependent photoluminescence (PL) spectra of the ZnTe epilayer grown on (100) GaAs substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the GaAs substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor–acceptor pair (DAP) nor conduction band-acceptor (e–A) emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal. [ABSTRACT FROM AUTHOR]

A simple and effective approach to improve the switching characteristics of AlGaN/AlN/GaN heterostructure field effect transistors (HFETs) by applying a voltage bias on the substrate is presented. With the increase of the substrate bias, the OFF-state drain current is much reduced and the ON-state current keeps constant. Both the ON/OFF current ratio and the subthreshold swing are demonstrated to be greatly improved. With the thinned substrate, the improvement of the switching characteristics with the substrate bias is found to be even greater. The above improvements of the switching characteristics are attributed to the interaction between the substrate bias induced electrical field and the bulk traps in the GaN buffer layer, which reduces the conductivity of the GaN buffer layer. [ABSTRACT FROM AUTHOR]

Nonalloyed ohmic contacts regrown by metal-organic chemical vapor deposition are performed on AlGaN/GaN high-electron-mobility transistors. Low ohmic contact resistance of 0.15ω·mm is obtained. It is found that the sidewall obliquity near the regrown interface induced by the plasma dry etching has great influence on the total contact resistance. The fabricated device with a 100-nm T-shaped gate demonstrates a maximum drain current density of 0.95 A/mm at Vgs = 1 V and a maximum peak extrinsic transcondutance Gm of 216 mS/mm. Moreover, a current gain cut-off frequency fT of 115 GHz and a maximum oscillation frequency fmax of 127 GHz are achieved. [ABSTRACT FROM AUTHOR]

We report on an improved metal-graphene ohmic contact in bilayer epitaxial graphene on a SiC substrate with contact resistance below 0.1 ω·mm. Monolayer and bilayer epitaxial graphenes are prepared on a 4H-SiC substrate in this work. Their contact resistances are measured by a transfer length method. An improved photoresist-free device fabrication method is used and is compared with the conventional device fabrication method. Compared with the monolayer graphene, the contact resistance Rc of bilayer graphene improves from an average of 0.24 ω·mm to 0.1 ω·mm. Ohmic contact formation mechanism analysis by Landauer's approach reveals that the obtained low ohmic contact resistance in bilayer epitaxial graphene is due to their high carrier density, high carrier transmission probability, and p-type doping introduced by contact metal Au. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) properties of a green and blue light-emitting InGaN/GaN multiple quantum well structure with a strong phase separated into quasi-quantum dots (QDs) and an InGaN matrix in the InGaN epilayer are investigated. The excitation power dependences of QD-related green emissions (PD) and matrix-related blue emissions (PM) in the low excitation power range of the PL peak energy and line-width indicate that at 6 K both PM and PD are dominated by the combined action of Coulomb screening and localized state filling effect. However, at 300 K, PM is dominated by the non-radiative recombination of the carriers in the InGaN matrix, while PD is influenced by the carriers transferred from the shallower QDs to deeper QDs by tunnelling. This is consistent with the excitation power dependence of the PL efficiency for the emission. [ABSTRACT FROM AUTHOR]

In this study, we investigate the effects of GaN cap layer thickness on the two-dimensional electron gas (2DEG) electron density and 2DEG electron mobility of AlN/GaN heterostructures by using the temperature-dependent Hall measurement and theoretical fitting method. The results of our analysis clearly indicate that the GaN cap layer thickness of an AlN/GaN heterostructure has influences on the 2DEG electron density and the electron mobility. For the AlN/GaN heterostructures with a 3-nm AlN barrier layer, the optimized thickness of the GaN cap layer is around 4 nm and the strained a-axis lattice constant of the AlN barrier layer is less than that of GaN. [ABSTRACT FROM AUTHOR]