N极性GaN薄膜的MOCVD外延生长

采用MOCVD技术在c面蓝宝石衬底上外延制备了N极性GaN薄膜。通过KOH腐蚀的方法判定了GaN外延薄膜的极性。通过X射线双晶衍射(XRD)摇摆曲线和光致荧光(PL)谱测试研究了成核层生长时间对N极性GaN薄膜晶体质量和发光性能的影响。研究结果表明,成核层生长时间为300 s时,N极性GaN薄膜样品的位错密度最低,发光性能最好。采用拉曼(Raman)光谱对样品的应变状态进行了分析。     

常压MOCVD生长ZnO薄膜及其性质

用常压MOCVD在蓝宝石 (0 0 0 1)面上生长了氧化锌 (ZnO)薄膜。用AFM、室温PL谱、Hall测量、X射线双晶衍射、卢瑟福背散射 /沟道技术等分析方法研究了样品的表面形貌、结构性能、发光性能和电学性能。AFM分析结果显示 ,薄膜呈六角柱状结晶 ,表面平整 ,粗糙度 (RMS)为 6 .2 5 7nm ,平均晶粒直径达 1.895 μm。室温PL测量该样品在 380nm处有很强的近带边发射 ,半峰全宽为 15nm。使用Hall测量检查了薄膜的电学性质。室温下该样品的载流子浓度为 2× 10 17cm-3 ,迁移率为 75cm2 ·V-1·s-1。用X射线双晶衍射和卢瑟福背散射 /沟道效应研究了薄膜的结晶质量 ,样品的双晶衍射ω扫描半峰全宽为 0 .0 4° ,沟道效应的最小产额比χmin为 3.1%。     

组份变化的InGaAsSb/AlGaAsSb多量子阱结构对其X射线衍射及发光性质的影响

通过二元系和三元系结构参数计算四元系量子阱结构的晶格常数、禁带宽度等,设计了InGaAsSb/AlGaAsSb结构的MBE生长参数及工艺,利用X射线双晶衍射和PL谱研究了InGaAsSb/AlGaAsSb多量子阱结构特性和光学特性。X射线双晶衍射谱中出现了8条卫星峰,表明制备的InGaAsSb/AlGaAsSb多量子阱结构具有良好的结晶质量。利用光致发光光谱方法对制备的样品的光学性质进行了表征,结果表明,不同组份的InGaAsSb/AlGaAsSb多量子阱的发光峰波长随组份的变化在1.6~2.28 μm范围内可调,样品PL谱的半峰宽最窄可达22 meV。     

外延在蓝宝石衬底上的非掺杂GaN研究

采用改变生长条件的方法制备GaN薄膜,在(0001)面蓝宝石衬底上利用金属有机物化学气相沉积技术制备了不同样品,并借助X射线双晶衍射仪(XRD)、PL谱测试仪和光学显微镜对材料进行了分析。XRD(0002)面和(1012)面测试均表明TMGa流量为70 cm3/min时样品位错密度最低。利用该TMGa流量进一步制备了改变生长温度的样品。XRD和PL谱测试结果表明,提高生长温度有利于提高GaN样品的晶体质量和光学性能。最后,利用光学显微镜对样品的表面形貌进行了分析。     

常压MOCVD生长ZnO/GaN/Al2O3薄膜及其性能

以去离子水（H2O）和二乙基锌（DEZn）为源材料,生长温度是680℃时,利用常压MOCVD在GaN／Al2O3模板上成功生长了ZnO单晶薄膜,用原子力显微镜（AFM）、X射线双晶衍射（DCXRD）、光致发光谱（PL）对ZnO薄膜的表面形貌、结晶学性质、光学性质作了综合研究。双晶衍射表明,ZnO非对称（1012）面ω扫描的半峰全宽（FWHM）仅为420arcsec,估算所生长ZnO膜的位错密度大约为10^3／cm^2量级,这与具有器件质量的GaN材料的位错密度相当。在ZnO薄膜的低温15K光荧光谱中,观察到很强的自由激子和束缚激子发射以及自由激子与束缚激子的多级声子伴线。     

InGaAsSb/InP的MBE生长及特性

研究了InP基InGaAsSb外延材料受生长温度和Ⅴ/Ⅲ比的影响。实验中利用高能电子衍射(RHHEED)监测获得了合适的生长温度和Ⅴ/Ⅲ比,采用扫描电子显微镜 (SEM)、X射线光电子能谱(XPS)、X射线双晶衍射(XRDCD)和光致发光(PL)谱等方法研究了InGaAsSb薄膜材料的表面形貌、结晶质量和发光特性。通过控制生长温度和Ⅴ/Ⅲ比,获得了X射线衍射峰半峰全宽较窄的高质量的外延材料。     

氮化蓝宝石衬底上GaN薄膜的微结构与光学性质

用透射电子显微镜(TEM),X射线衍射(XRD)和光荧光谱(PL)等测量手段研究了GaN薄膜的微结构和光学性质。样品是用光辐射加热MOCVD在蓝宝石衬底上制备的。随着衬底氮化时间的增加,扩展缺陷的密度显著增加。在位错密度增加一个数量级时,XRD摇摆曲线半宽度(FWHM)由11″增加到15″,PL谱的黄光发射从几乎可忽略增加到带边发射强度的100倍。结合生长条件,我们对黄光与微结构的关系作了讨论。     

应力和掺杂对Mg:GaN薄膜光致发光光谱影响的研究

对化学气相沉积(MOCVD)法在宝石衬底上生长的Mg掺杂GaN薄膜的表面及其GaN缓冲层的光致发光(PL)光谱进行了测量，用Raman光谱和x射线衍射(XRD)对GaN薄膜中的应力进行确定，通过PL光谱中的中性束缚激子跃迁能量的变化确定薄膜中应力的影响，从而研究Mg掺杂对p型GaN的DAP跃迁影响规律. 关键词： 光致发光 应力 Raman光谱     

InGaN/GaN多量子阱的组分确定和晶格常数计算

采用金属有机化学气相沉积(MOCVD)技术以蓝宝石为衬底在n型GaN单晶层上生长了InGaN/GaN多量子阱结构外延薄膜，利用高分辨X射线衍射(HRXRD)，卢瑟福背散射/沟道(RBS/channeling)，以及光致发光(PL)技术对InGaN/GaN多量子阱结构薄膜分别进行了平均晶格常数计算、In原子替位率计算和In组分的定量分析.研究表明：InGaN/GaN多量子阱的水平和垂直方向平均晶格常数分别为a_epi=0.3195nm，c_epi=0.5198nm，In原子的替位率为99.3%，利用HRXRD和RBS/channeling两种分析技术计算In的组分分别是0.023和0.026，并与样品生长时设定的预期目标相符合，验证了两种实验方法的准确性；而用室温条件下的光致发光谱(PL)来计算InGaN/GaN多量子阱中In的组分是与HRXRD和RBS/channeling的实验结果相差很大，说明用PL测试In组分的方法是不适宜的. 关键词： InGaN/GaN多量子阱 高分辨X射线衍射 卢瑟福背散射/沟道 光致发光     

气流混合对生长GaN：Si膜性能影响的研究

用金必有机化学气相沉积技术在三种不同型号的反应管中生长了GaN:Si膜。通过对样品的光电及结晶性能的分析，研究了气流混合时间不同对GaN:Si膜性质的影响。结果表明：合理的Ⅲ、Ⅴ族气流混合对提高GaN:Si膜的光电及结晶性能很重要。Ⅲ、Ⅴ族气流混合太早，气流混合时间长，GaN:Si膜的黄带与发射强度之比较大，X射线双晶衍射半高宽；Ⅲ、Ⅴ族气流混合太晚，尽管可减少预反应，但气流混合不均匀，致使GaN:Si膜的发光性能及结晶性能变差。使用Ⅲ、Ⅴ族气流混合适中的反应管B生长、获得了光电及结晶性能良好的CaN:Si单晶膜。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.