A1/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage （I-V） characteristics of Al/Ti/4H-SiC Schottky barrier diodes （SBDs） in the temperature range of 77 K-500 K, which shows that Al/Ti/4H SiC SBDs have good rectifying behaviour. An abnormal behaviour, in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature （T）, has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the A1/Ti/4H-SiC interface. The effective Richardson constant A＊ = 154 A/cm2 . K2 is determined by means of a modified Richardson plot In（I0/T2） - （qσ）2/2（κT）2 versus q/kT, which is very close to the theoretical value 146 A/cm2 · K2.     

Robust Generation of Three-Particle W State with Atoms Trapped in Separate Cavities

This paper presents a scheme for generating three-particle W state of remote atoms trapped in leaky cavities.The scheme uses cavity decay to inject photons into a setup of optical devices which consist of a series of beam splitters and photon detectors.Photon detection on the output mode projects the atomic state into the W state.In the condition of “weakly driven approach”,it shows that the scheme is robust and has high fidelity.It also points out that the scheme is scalable to generate multi-atomic W state.     

N型4H-SiC同质外延生长

利用水平式低压热壁CVD (LP-HW-CVD) 生长系统,台阶控制生长和衬底旋转等优化技术,在偏晶向的4H-SiC Si(0001) 晶面衬底上进行4H-SiC同质外延生长,生长温度和压力分别为1550℃和10⁴ Pa,用高纯N₂作为n型掺杂剂的4H-SiC原位掺杂技术,生长速率控制在5μm/h左右.采用扫描电镜(SEM)、原子力显微镜(AFM),傅里叶变换红外光谱(FTIR)和Hg/4H-SiC肖特基结构对同质外延表面形貌、厚度、掺杂浓度以及均匀性进行了测试.实验结果表明,4H-SiC同质外延在表面无明显缺陷,厚度均匀性1.74%, 1.99% 和1.32%(σ/mean),掺杂浓度均匀性为3.37%,2.39%和2.01%.同种工艺条件下,样品间的厚度和掺杂浓度误差为1.54%和3.63%,有很好的工艺可靠性. 关键词： 4H-SiC 同质外延生长 水平热壁CVD 均匀性     

An online method combining a thermal conversion elemental analyzer with isotope ratio mass spectrometry for the determination of hydrogen isotope composition and water concentration in geological samples

An online continuous-flow method, combining a thermal conversion elemental analyzer (TC/EA) with isotope ratio mass spectrometry (MS), is evaluated for the determination of both the hydrogen isotope composition and the water concentration of hydrous and nominally anhydrous minerals. The technique involves reduction of hydrous minerals or nominally anhydrous minerals by reaction with glassy carbon at 1450 degrees C in a helium stream. The product gases, H2 and CO, are separated on a gas chromatographic column prior to analysis in the mass spectrometer. Calibration curves for the H concentration analysis were generated from a standard of benzoic acid (C7H6O2) that has an H concentration of 5.0 wt%; the analytical uncertainties were better than +/-0.05% in our runs. Two standards of material with given D values, polyethylene IAEA-CH-7 and biotite NBS-30, were tested for the purpose of calibrating a natural garnet 04BXL02 representing nominally anhydrous minerals. Preheating at 90 degrees C for 12 h was found to be suitable for removing adsorption water on the sample surface. This results in constant D values and total H2O contents for the garnet, with weighted means of -94 +/- 1 and 522 +/- 11 ppm (wt), respectively. The TC/EA-MS technique allows routine analysis of sample sizes as small as 0.01 microL H2O. For natural minerals, absolute reproducibilities for D values are +/-0.5 to +/-2 (1) and relative uncertainties for total H2O concentrations are at levels of +/-1% to +/-3% (1). Therefore, this online method can be used for the quantitative determination of H isotope composition and H2O concentration of either hydrous or anhydrous minerals.     

Investigation of 4H—SiC metal—insulation—semiconductor structure with Al2O3/SiO2 stacked dielectric

Atomic layer deposited (ALD) Al₂O₃/dry-oxidized ultrathin SiO₂ films as high-k gate dielectric grown on the 8° off-axis 4H-SiC (0001) epitaxial wafers are investigated in this paper. The metal-insulation-semiconductor (MIS) capacitors, respectively with different gate dielectric stacks (Al₂O₃/SiO₂, Al₂O₃, and SiO₂) are fabricated and compared with each other. The I-V measurements show that the Al₂O₃/SiO₂ stack has a high breakdown field ( ≥ 12 MV/cm) comparable to SiO₂, and a relatively low gate leakage current of 1× 10^-7 A/cm² at electric field of 4 MV/cm comparable to Al₂O₃. The 1-MHz high frequency C-V measurements exhibit that the Al₂O₃/SiO₂ stack has a smaller positive flat-band voltage shift and hysteresis voltage, indicating less effective charge and slow-trap density near the interface.     

动态应力下超薄栅氧化层经时击穿的可靠性评价

实验发现动态电压应力条件下,由于栅氧化层很薄,高电平应力时间内隧穿入氧化层的电子与陷落在氧化层中的空穴复合产生中性电子陷阱,中性电子陷阱辅助电子隧穿.由于每个周期的高电平时间较短(远远低于电荷的复合时间),隧穿到氧化层的电子很少,同时低电平应力时间内一部分电荷退陷,形成的中性电子陷阱更少.随着应力时间的累积,中性电子陷阱达到某个临界值,栅氧化层突然击穿.高电平时形成的陷阱较少和低电平时一部分电荷退陷,使得器件的寿命提高. 关键词： 超薄栅氧化层 斜坡电压 经时击穿     

Investigation of a 4H-SiC metal-insulation-semiconductor structure with an Al2O3/SiO2 stacked dielectric

Atomic layer deposited(ALD) Al2O3 /dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8°off-axis 4H-SiC(0001) epitaxial wafers are investigated in this paper.The metal-insulation-semiconductor(MIS) capacitors,respectively with different gate dielectric stacks(Al2O3/SiO2,Al2O3,and SiO2) are fabricated and compared with each other.The I-V measurements show that the Al2O3/SiO2 stack has a high breakdown field(≥12 MV/cm) comparable to SiO2,and a relatively low gate leakage current of1×10-7A/cm2 at an electric field of4 MV/cm comparable to Al2O3.The 1-MHz high frequency C-V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage,indicating a less effective charge and slow-trap density near the interface.     

4H-SiC同质外延生长Grove模型研究

本文通过对4H-SiC同质外延化学反应和生长条件的分析,建立了4H-SiC同质外延生长的Grove模型,并结合实验结果进行了分析和验证.通过理论分析和实验验证,得到了外延中氢气载气流量和生长温度对4H-SiC同质外延生长速率的影响.研究表明:外延生长速率在衬底直径上为碗型分布,中心的生长速率略低于边缘的生长速率;随着载气流量的增大,生长速率由输运控制转变为反应速率控制,生长速率先增大而后逐渐降低;载气流量的增加,会使高温区会发生漂移,生长速率的理论值和实验出现一定的偏移;随着外延生长温度的升高,化学反应速率和气相转移系数都会增大,提高了外延速率;温度对外延反应速率的影响远大于对生长质量输运的影响,当温度过分升高后,外延生长会进入质量控制区;但过高的生长温度导致源气体在生长区边缘发生反应,生成固体粒子,使实际参与外延生长的粒子数减少,降低了生长速率,且固体粒子会有一定的概率落在外延层上,严重影响外延层的质量.通过调节氢气流量,衬底旋转速度和生长温度,可以有效的控制外延的生长速度和厚度的均匀性.     

Periodic solitons in dispersion decreasing fibers with a cosine profile

Periodic solitons are studied in dispersion decreasing fibers with a cosine profile. The variable-coefficient nonlinear Schr¨odinger equation, which can be used to describe the propagation of solitons, is investigated analytically. Analytic soliton solutions for this equation are derived with the Hirota’s bilinear method. Using the soliton solutions, we obtain periodic solitons, and analyze the soliton characteristics. Influences of physical parameters on periodic solitons are discussed. The presented results can be used in optical communication systems and fiber lasers.     

高k介质异质栅全耗尽SOI MOSFET二维解析模型

为了研究高介电常数(高k)栅介质材料异质栅中绝缘衬底上的硅和金属-氧化物-硅场效应晶体管的短沟道效应,为新结构器件建立了全耗尽条件下表面势和阈值电压的二维解析模型.模型中考虑了各种主要因素的影响,包括不同介电常数材料的影响,栅金属长度及其功函数变化的影响,不同漏电压对短沟道效应的影响.结果表明,沟道表面势中引入了阶梯分布,因此源端电场较强;同时漏电压引起的电势变化可以被屏蔽,抑制短沟道效应.栅介电常数增大,也可以较好的抑制短沟道效应.解析模型与数值模拟软件ISE所得结果高度吻合. 关键词： 异质栅 绝缘衬底上的硅 阈值电压 解析模型