Near-field characterization of chemical vapor deposition graphene in the microwave regime

Near-field measurements were performed at X-band frequencies for graphene on copper microstrip transmission lines. An improvement in radiation of 0.88 dB at 10.2 GHz is exhibited from the monolayer graphene antenna which has dc sheet resistivity of 985 Ω/sq. Emission characteristics were validated via ab initio simulations and compared to empirical findings of geometrically comparable copper patches. This study contributes to the current knowledge of the electronic properties of graphene. © 2013 AIP Publishing LLC.

Unusual temperature-dependent optical properties of self-organized InAs/GaAs quantum dots at high excitation power

The temperature-dependent photoluminescence (PL) properties of InAs/GaAs self-organized quantum dots (QDs) have been investigated at high excitation power. The fast redshift of the ground-state and the first excited-state PL energy with increasing temperature was observed. The temperature-dependent linewidth of the QD ground state with high carrier density is different from that with low carrier density. Furthermore, we observed an increasing PL intensity of the first excited state of QDs with respect to that of the ground state and demonstrate a local equilibrium distribution of carriers between the ground state and the first excited state for the QD ensemble at high temperature (T > 80 K). These results provide evidence for the slowdown of carrier relaxation from the first excited state to the ground state in InAs/GaAs quantum dots.

Optical properties and band lineup in GaNxAs1-x/GaAs single quantum wells

The optical properties and the band lineup in GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL) technique were investigated. It was found that the low-temperature PL is dominated by the intrinsic localized exciton emission. By fitting the experimental datawith a simple calculation, band offset of the GaN0.015As0.985/GaAs heterostructure was estimated. Moreover, DeltaE(c), the discontinuity of the conduction band was found to be a nonlinear function of the nitrogen composition (chi) and the average variation of DeltaE(c) is about 0. 110eV per % N, such smaller than that reported on the literature to (0.156 similar to 0.175 eV/N %). In addition, Qc has little change whtn N composition increares, with an experimential relation of QC approximate tox(0.25). The band bowing coefficient (b) was also studied in this paper. The measured band bowing coefficient shows a strong function of chi, giving an experimental support to the theoretic calculation of Wei Su-Huai and Zunger Alex (1996).

Monolithic Integration of Light Emitting Diodes, Photodetector and Receiver Circuit in Standard CMOS Technology

A monolithic silicon CMOS optoelectronic integrated circuit (OEIC) is designed and fabricated with standard 0.35 mu m CMOS technology. This OEIC circuit consists of light emitting diodes (LED), silicon dioxide waveguide, photodiodes and receiver circuit. The silicon LED operates in reverse breakdown mode and can be turned on at 8.5V 10mA. The silicon dioxide waveguide is composed of multiple layers of silicon dioxide between different metals layers. A two PN-junctions photodetector composed of n-well/p-substrate junction and p(+) active implantation/n-well junction maximizes the depletion region width. The readout circuitry in pixels is exploited to handle as small as 0.1nA photocurrent. Simulation and testing results show that the optical emissions powers are about two orders higher than the low frequency detectivity of silicon CMOS photodetcctor and receiver circuit.

A new frequency offset estimation for OFDM-based systems

A new carrier frequency offset estimation scheme in orthogonal frequency division multiplexing (OFDM) is proposed. The scheme includes coarse frequency offset estimation and fine frequency offset estimation. The coarse frequency offset estimation method we present is a improvement of Zhang's method. The estimation range of the new method is as large as the overall signal-band width. A new fine frequency offset estimation algorithm is also discussed in this paper. The new algorithm has a better performance than the Schmidl's algorithm. The system we use to calculate and simulate is based on the high rate WLAN standard adopted by the IEEE 802.11 stanidardization group. Numerical results are presented to demonstrate the performance of the proposed algorithm.

短消息指标新定义及在事务信道限制中的应用

短消息指标可以度量隐蔽信道的短消息传输能力,是信道容量的必要补充.但指标现有定义中还存在着以下问题:消息长度参数在普通信息系统中不能定量分析;信道限制机制难以同时满足传输时间和保真度两个约束;没有包含消息的敏感度信息.针对这些问题,首先通过引入短消息传输价值的概念,给出了短消息指标的新定义.在该定义中,利用价值阈值统一表示系统对信道短消息传输能力的容忍程度,并且在所采用的价值函数中引入了消息的敏感度因素.其后,基于安全实时数据库应用场景给出了结合短消息指标和信道容量的事务隐蔽信道度量和限制机制.理论分析和模拟结果表明,基于短消息指标的新定义,系统可以对隐蔽信道威胁实施全面的度量和可调节的限制.

基于自定义状态机制的需求管理工具的研究与实现

分析了需求管理中需求项的状态属性特点,针对现有的软件需求管理工具对此处理的局限性,结合国内从事软件开发组织的实际需求,提出了在需求管理工具引入状态定制的思想,并结合数据库中元数据的概念,实现了在需求管理工具RMT中的自定义状态机制。

带V形隔热膜封闭空间内自然对流换热的数值研究

本文通过涡量-流函数法，对带V形隔热膜的平板型太阳能集热器二维封闭空间内自然对流进行了数值计算，定量分析了Rα、集热器倾角、V形膜开口角、H_v/H四个参数对换热的影响，为这种集热器的设计提供了依据。

与标准集成电路工艺兼容的硅基光学器件研究

着重介绍了与标准集成电路工艺兼容的硅基光学器件的最新研究进展,包括硅基光发射器、硅基光波导和调制器件、硅基光电探测器和接收机以及硅基光电子集成回路的工作原理、制作工艺和集成技术.与标准集成电路工艺兼容的硅基光电子集成回路能有效地解决电互连芯片内部串扰、带宽和能耗等问题,并能够充分利用现有成熟的集成电路工艺,实现大规模生产,具有广阔的实用前景.

LPCVD Growth of 3C-SiC on Si Mesas and SiO2/Si Substrates for MEMS Applications

This paper presents the development of LPCVD growth of 3C-SiC thin films grown on Si mesas and thermally oxidized SiO2 masks over Si with an area of 150 × 100μm^2 and SiO2/Si substrates. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H2. 3C-SiC films on these substrates were characterized by optical microscopy, X-ray diffraction （ XRD ）, X-ray photoelectron spectroscopy （ XPS ）, scanning electron microscopy （SEM） and room temperature Hall effect measurements. It is shown that there were no voids at the interface between 3C-SiC and SiO2.

基于电吸收调制器波长变换技术的实验研究

实现了基于国产电吸收调制器中交叉吸收调制效应的波长变换，波长变换范围超过30nm，同时对实现波长变换的工作投机倒把进行了实验研究。

GaNAs/GaAs量子阱的静压光致发光研究

在15K和0-9GPa静压范围下测量了GaN0.015As0.985/GaAs量子阱的光致发光谱。观察到了GaNAs阱和GaAs垒的发光，发现GaNAs阱发光峰随压力的变化比GaAs垒发光峰要小很多。当压力超过2.5GPa后还观察到了与GaAs中的N等电子陷阱有关的一组新发光峰。用二能级模型及测得的GaAs带边和N等电子能级的压力行为计算了GaNAs发光峰随压力的变化，但计算结果与实验结果相差甚大，表明二能级模型并不安全适用。对观察到的GaNAs发光峰的强度和半宽随压力的变化也进行了简短讨论。

Optical transitions in GaNAs/GaAs single quantum well

We have investigated GaNAs/GaAs single quantum wells (SQWs) grown by molecular beam epitaxy (MBE) using photoluminescence (PL), time-resolved PL (TRPL) and photovoltaic (PV) techniques. The low temperature PL is dominated by spatially direct transitions involving electrons confined in GaNAs well and holes localized in the same GaNAs layer. This assignment was supported by PL decay time measurements and absorption line-shape analysis derived from the PV measurements. By fitting the experimental data with a simple calculation, the band offset of the GaN0.015As0.985/GaAS heterostructure was estimated, and a type II band lineup in GaN0.015As0.985/GaAs QWs was suggested. Moreover, DeltaE(C), the discontinuity of conductor band, is found to be a nonlinear function of the nitrogen (N) composition (x), and the average variation of DeltaE(C) is about 0.110eV per %N, The measured band bowing coefficient shows a strong function of x, giving an experimental support to the theoretic calculation of Wei et al [Ref.2].