MOCVD生长的未掺杂GaN的结晶特性与补偿度关系的研究

对本实验室用ＭＯＣＶＤ方法生长的未故意掺杂的ＧａＮ单晶膜进行了结晶性能、电学性能研究。结果表明,室温时ＧａＮ的Ｘ射线双晶衍射半高宽与其补偿度有较强的依赖关系。高补偿的ＧａＮ的Ｘ射线双晶衍射半高宽较宽。低补偿的ＧａＮ的Ｘ射线双晶衍射半高宽较窄。     

MOCVD生长的GaN单晶膜的蓝带发光研究

对实验室用ＭＯＣＶＤ方法生长的未掺杂ＧａＮ单晶膜的发光性能进行了研究。结果表明：在室温时未掺杂ＧａＮ单晶出现的能量为２．９ｅＶ左右蓝带发光与被偿度有较强的依赖关系。高补偿ＧａＮ的蓝带发射强,低补偿ＧａＮ的蓝带发射弱。对蓝带发光机理进行了探讨,认为蓝 导带电子过至受主能级的发光（ｅＡ发光）。观察到降低ＧａＮ补偿度能提高ＧａＮ带边发射强度。     

MOCVD生长GaN:Si单晶膜的研究

获得高质量的ｎ型ＧａＮ单晶膜是制作ＧａＮ基光电子器件的关键之一。采用立式ＭＯＣＶＤ系统生长ＧａＮ：Ｓｉ单晶膜,通过优化生长工艺,获得了电子载流于浓度高达２ ×１０１９ｃｍ－３,迁移率达１２０ｃｍ２／Ｖ·ｓ的ｎ型ＧａＮ：Ｓｉ单晶膜;并有效地抑制了ＧａＮ中由深能级引起的黄带发射,大大提高带边发光强度。研究结果还表明：随着Ｓ掺杂量的增大,ＧａＮ：Ｓｉ单晶膜的电子载流于浓度增加,迁移率下降,Ｘ光双晶衍射峰半高宽增大。首次报道了随掺Ｓ量增大,ＧａＮ：Ｓｉ单晶膜的生长速率显著下降的现象。     

GaN外延层中的缺陷对光学性质的影响

用金属有机化合物气相外延（ＭＯＶＥＰ）方法生长具有不同表面形貌的非掺杂ＧａＮ，并对部分样品的外延层表面进行镜面加工．用阴极射线发光、光散射和拉曼散射方法观察ＧａＮ中深能级发光、缺陷散射光分布和拉曼散射光频移．结果表明，缺陷不但影响ＧａＮ的发光和光散射，而且影响拉曼频移     

高质量GaN外延薄膜的生长

综述了高质量ＧａＮ外延薄膜的生长研究工作的最新重要进展．主要采用的新工艺为：在较低温度下生长ＧａＮ缓冲层后再高温生长ＧａＮ外延薄膜,双气流金属有机化合物气相沉积（ＭＯＣＶＤ）,以及用开有窗口的ＳｉＯ２膜截断穿过位错后横向覆盖外延生长（ｅｐｉｔａｘｉａｌｙｌａｔｅｒａｌｏｖｅｒｇｒｏｗｔｈ）．Ｘ射线衍射和高分辨电镜研究证实,上述工艺使ＧａＮ外延薄膜质量得到显著提高．利用这种薄膜研制成的蓝色激光管即将投放市场．     

GaN激子跃迁的时间分辨光谱学研究

用时间分辨光谱学方法研究低压有机金属化学汽相沉积生长的ＧａＮ中自由，束缚激子（ＢＸ）的跃迁，讨论了这些跃迁的光致发光谱，复合寿命及其与温度的关系，给出了中性施主束缚激子和自由激子（ＦＸ）的辐射复合寿命分别为０．１２ｎｓ和０．４ｎｓ。     

GaN光学微盘的显微荧光图像探讨

研制了不同厚度的直径为５－１５μｍ的ＧａＮ光学微盘,并 学微盘的显微荧光图像进行了细致观测和数据值采集。结果表明,在同一个ＧａＮ外延样品上由于厚度的差别,微盘呈现两种不同类型的荧光图像,     

新型蓝光衬底材料LiAlO2晶体的生长的缺陷分析

ＬｉＡｌＯ２和ＧａＮ的晶格失配率只有１．４％，是一种很有希望的ＧａＮ外延生长衬底材料。本文利用温度梯度法生长出透明的ＬｉＡｌＯ２单晶，并通过化学浸蚀、光学显微镜、透射电子显微镜、同步辐射Ｘ射线貌相术对晶体中的缺陷进行了检测。结果表明：ＬｉＡｌＯ２在钼坩埚中无籽晶自由凝固结日地，是沿（１００）方向生长。用温度梯度法生长的ＡｉＡｌＯ２晶体质量良好，晶体中无气泡和包裹物，在ＬｉＡｌＯ２（１００）方向晶面     

金属有机化合物相外延生长GaN薄膜的电子微结构研究

研究了金属有机化合物气相外延（ＭＯＶＰＥ）方法在（０００１）氧化铝基底上生长的ＧａＮ薄膜的微结构，目的在于解释ＧａＮ缓冲层在二步法生和过程中的作用及其对外延层晶体质量的影响。在缓冲层中观察到了高密度的结构缺陷，并发现了两种晶体结构（立方和六角）的ＧａＮ。进而对两种结构ＧａＮ的成因进行讨论，并对缓冲层和外延层中结构缺陷的关系进行了研究。     

GaN异质外延的离子化氮源方法

用电离Ｎ_２产生的离子束作为外延生长氮化物的Ｎ源已获得成功，在ＧａＡｓ（１００）衬底上长出了具有立方结晶的ＧａＮ薄膜，其（２００）X射线衍射峰宽仅２３′。并用高分辨率电子能量损失谱测到立方ＧａＮ的表面光学声子出现在损失能量为８２ｍｅＶ处． 关键词：     

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.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

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.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.