基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系，考虑到非辐射复合的影响，从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

降低VCSELs激射阈值途径的理论研究

针对量子阱有源层的结构特点，考虑增益和载流子浓度呈对数关系，建立量子陆垂直腔面发射半导体激光器（VCSEL）的速率方程，导出了阈值电流密度的解析表达式，运用MATLAB软件中Simulink可视化仿真系统对理论计算进行模拟仿真，研究了降低VCSEL激射阈值的3个基本途径；有源层选用量子阱实现微腔结构，腔面采取多层介质反射膜提高光腔反射率R：改进外延生长技术在降低各种损耗。     

基于对数关系的多量子阱VCSELs阈值特性研究

采用光增益与载流子浓度的对数关系,考虑到非辐射复合的影响,从理论上推导出多量子阱垂直腔面发射半导体激光器(VCSELs)的速率方程。讨论了阈值电流密度、最佳阱数等与器件参数(腔长和端面反射率)之间的依赖关系。为改善VCSELs阈值特性和优化器件结构提供了理论依据。     

一种850nm氧化限制型垂直腔面发射激光器的设计

采用PICS3D软件建立了850 nm氧化限制型垂直腔面发射激光器(VCSEL)的仿真模型,通过优化量子阱有源区的阱和垒的个数、合理选取分布式布拉格反射镜(DBR)的材料以及对数,设计了一种850 nm氧化限制型VCSEL.在10μm氧化孔径下,与商用的850 nm氧化限制型VCSEL相比,其阈值电流从1.8mA降至1.5mA,斜率效率从0.3 W/A提升到0.65 W/A.     

多量子阱VCSELs阈值特性的分析

采用光增益与载流子浓度的对数关系,从理论上推导出量子阱垂直腔面发射半导体激光器的速率方程。比较了三维理想封闭腔与普通开腔中的特性曲线这将对于ＶＣＳＥＬｓ的理论研究和优化器件结构有所裨益。     

垂直腔面发射激光器的研究进展及其应用

垂直腔面发射激光器(VCSEL)具有常规半导体激光器不可比拟的优点：其光束是园形的,易于实现与光纤的高效耦合;VCSEL的有源区尺寸可做得非常小,以获得高封装密度和低阈值电流;适宜的设计可将激光二极管制成简单的单片集成二维列阵,以实现二维光数据处理所用的激光源;芯片生长后无须解理、封装即可进行在片实验。由于VCSEL的优良性能,从而获得了国内外科技界、企业界的高度关注。本对这种器件的性能、开发现状及应用作简要的概述。     

新型垂直腔面发射激光器的研制北大核心CSCD

热问题是制约垂直腔面发射半导体激光器(VCSEL)的关键难题之一。为改善垂直腔面发射激光器的热特性,提高输出功率,设计并制备了一种新型内腔接触式结构VCSEL。在出光孔径为16μm时,同时制备传统结构和新型结构两种器件并对其进行测试,传统结构VCSEL的阈值电流为11.5 mA,当注入电流为34 mA时,最大输出功率达到7.3 mW;新结构器件的阈值电流为9 mA,当注入电流为35 mA时,最大输出功率达到10.2 mW;新结构的阈值电流降低了21.7%,最大输出功率提高了28%。结果表明,这种内腔接触式电极结构有望改善器件的热特性和光电性能。     

980 nm高功率垂直腔面发射激光器

研究了 980nm垂直腔面发射激光器 (VCSEL)的结构设计和器件制作 ,实现了室温下的脉冲激射。在脉宽为 5 0 μs,占空比为 5∶10 0 0的脉冲电流下 ,直径 4 0 0 μm的器件输出光功率最高可达 380mW ,发散角小于 10° ,光谱的半高全宽为 0 8nm。     

GaAs/AlGaAs环形激光器的量子阱结构优化

为了研究量子阱结构对半导体环形激光器阈值电流的影响,从F-P腔激光器的振荡条件出发,分析了半导体环形激光器的阈值电流密度与量子阱结构参量的函数关系,并推导出最佳量子阱数的表达式。利用器件仿真软件ATLAS建立环形激光器的等效模型,仿真、分析了不同工作温度下,量子阱数、阱厚及势垒厚度对阈值电流的影响。结果表明,阈值电流随量子阱数和阱厚的增加先减小后增大,存在一组最佳值;在确定合适的量子阱数和阱厚后,相对较窄的势垒厚度有助于进一步降低阈值电流;采用GaAs/AlGaAs材料体系和器件结构,其最佳量子阱结构参量为M=3,dw=20nm及db=10nm。     

新型垂直腔面发射激光器的研制

热问题是制约垂直腔面发射半导体激光器(VCSEL)的关键难题之一。为改善垂直腔面发射激光器的热特性,提高输出功率,设计并制备了一种新型内腔接触式结构VCSEL。在出光孔径为16μm时,同时制备传统结构和新型结构两种器件并对其进行测试,传统结构VCSEL的阈值电流为11.5 mA,当注入电流为34 mA时,最大输出功率达到7.3 mW;新结构器件的阈值电流为9 mA,当注入电流为35 mA时,最大输出功率达到10.2 mW;新结构的阈值电流降低了21.7%,最大输出功率提高了28%。结果表明,这种内腔接触式电极结构有望改善器件的热特性和光电性能。     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

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正Communications—VLSI Researches and industries of telecommunications have been growing rapidly in the last 20 years and will keep their high growing pace in the next decade.The involved researches and developments cover mobile communications,highway and last-mile broadband communication,domain specific communications,and emerging D2D M2M communications.Radio communication steps into its