Growth and characterization of high-quality LiAlO2 single crystal

g-LiAlO2 single crystal is a promising substrate for GaN heteroepitaxy. In this paper, we present the growth of large-sized LiAlO2 crystal by modified Czochralski method. The crystal quality was characterized by high-resolution X-ray diffraction and chemical etching. The results show that the as-grown crystal has perfect quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec and etch pits density of (0.3-2.2) x 10(4) cm(-2) throughout the crystal boule. The bottom of the crystal boule shows the best quality. The optical transmission spectra from UV to IR exhibits that the crystal is transparent from 0.2 to 5.5 mu m and becomes completely absorbing around 6.7 mu m wavelength. The optical absorption edge in near UV region is about 191 nm.

Low power 2 x 2 thermo-optic SOI waveguide switch fabricated by anisotropy chemical etching

A 2 x 2 thermo-optic (TO) Mach-Zehnder (MZ) switch based on silicon waveguides with large cross section was designed and fabricated on silicon-on-insulator (SOI) wafer. The multi-mode interferometers (MMI) were used as power splitter and combiner in MZ structure. In order to get smooth interface, anisotropy chemical wet-etching of silicon was used to fabricate the waveguides instead of dry-etching. Additional grooves were introduced to reduce power consumption. The device has a low switching power of 235 mW and a switching speed of 60 mus. (C) 2004 Elsevier B.V. All rights reserved.

Silicon-on-insulator based 2 x 2 multimode interference coupler with large tolerance

We demonstrate a type of 2 x 2 multimode interference 3 dB coupler based on silicon-on-insulator. The fabrication tolerance was investigated by the effective index method and the guide mode method. The devices with different lengths were fabricated and near-held output images were obtained. Tolerances to width, length and etch depth are 2, 200 and 2 mum, respectively. The devices show a uniform power distribution.

Fabrication of 2 x 2 tapered multimode interference coupler

The authors demonstrate a 3dB 2 x 2 parabolically tapered multimode interference (MMT) coupler with a large cross-section and space between the different ports using silicon-on-insulator technology. The device exhibits a uniformity of < 0.8dB and can be used in the realisation of an MMI-based optical switch with a high extinction ratio.

高Tc超导体R_1Ba_2Cu_3O_(2-x)(R-rare earth)的磁性和超异电性研究

本论文合成了R_1Ba_2Cu_3O_(2-x) (R = La、Nd、Sm、Eu、Gd、Dr、Ho、Er、Tm、Yb)、Y_2Ba_2Cu_3O_(2-x) (x = 0.10～1.17)和Y_1Ba_2Cu_3O_(7-x)S_x (x = 0～2)，并对磁性和超导电性进行了较为系统的研究。R_1Ba_2Cu_3O_(2-x)的磁化率在T > Tc的很宽的温度范围内服从Curic-Weiss定律，求得的有效磁矩略大于理论值，差值与Y_1Ba_2Cu_3O_(2-x)中Cu~(2+)磁矩相近，说明Cu~(2+)的磁矩对体系磁性有额外贡献，这贡献随R~(3+)离子中自旋平行的电子权的增多而增大。其高温下的磁化率CT > 700K)相对Curic-Weiss定律发生较大偏离，这偏离可能的来源有三个：高温下稀土离子发生较大的能级反转效应，高温下结构相变对磁性的影响，高温下氧含量减少造成Cu~(2+)磁矩增大。R_1Ba_2Cu_3O_(2-x)磁化率在T < Tc时也服从Curic-Weiss定律，R~(3+)磁矩是定域的，表明超导与磁性相互独立。互不相关，稀土磁矩与传导电子间无相互作用。用Sr取代R_1Ba_2Cu_3O_(2-x)中的Ba，没能使体系产生磁有序的变化，但却使有效磁矩增大，并完全破坏了样品的超导电性。Sm~(3+)磁化率不服从Curic-Weiss定律，在Sm_1Ba_2Cu_3O_(2-x)中Sm~(3+)显示了典型Van VlccK离子的特性。Y_1Ba_2Cu_3O_(2-x)随氧含量减少发生超导体一半导体一绝缘体的转化，当氧含量由6.90减小至6.49时发生由正交到四方的结构相变。当(7-x) = 5.83时有较多杂质相出现，123相开始分解。样品磁化率均服从Curic-Weiss定律，并随氧含量增大磁化率－温度曲线越来越趋于平缓（直线），当(7-x) = 6.90时磁化率基本不随温度变化，这时Pauli顺磁性占主导地位，这说明氧含量增加定域磁矩减少，求得的有效磁矩Peff随氧含量增大总趋势减小。提出了电子“巡游”的观点，较好地解释了上述现象，并推测出Cu(2)的d电子是离域的，对样品磁矩没有贡献，样品Peff来源于部分Cu(1)的定域Cu~(2+)的磁矩，上述推测被EPR结果证实。正交相Y_1Ba_2Cu_3O_(2-x)的EPR谱显示了中心对称成准立方晶场中Cu~(2+)(d~9, S = 1/2, I = 3/2)的EPR物性。而四方相样品的EPR谱却出现了明显的各向异性，说明观察到的为Cu(1)的EPR信号，由Cu(1)~(2+)的写域磁矩产生。Y_1Ba_2Cu_3O_(2-x)的EPR信号束源于本体相，而非Y_2Cu_2O_5、BaCuO_2、Y_2BaCuO_5等杂质相。各样品EPR信号的自旋浓度远小于1spin/cu，并随氧含量减小而增大，当(7-x) = 6.49、6.40时自旋浓度出现陡增，这时伴随由正交到四方的转化，证明了电子“巡游”观点的正确。用硫部分取代Y_1Ba_2Cu_3O_2g中的氧，当Y_1Ba_2Cu_3O_(2-x)Sx中x = 0.11时Tc = 92.6K，比Y_1Ba_2Cu_3O_(7-x)升高2K，但由于杂质相的存在，ΔTc加宽。其他样品多为半导体和绝缘体。硫取代0，当x = 0.04，0.06，0.11和1.20时磁化率服从Curic-Weiss定律，并且x = 0.87，1.2时分别在230K、240K出现反铁磁有序。其他样品由于Cu被还原为＋1价而变成抗磁性。x = 0.11 (Tc = 92.6K)，EPR谱为正交场中Cu~(2+)的信号。自旋浓度与温度无关。当所有Cu均为Cu~(1+)时，测问的是-s-的EPR信号，而Cu为混合价态(+1和+2时)测问是上述两种信号的叠加。

La-Ba-Cu-Sn-O钙钛矿型多元复合氧化物的制备、组成、结构、电学性质和气敏性质的研究

本文合成了LaBa_2Cu_(3-x)Sn_xO_(6.5) + x (x = 0.2; 0.5; 0.7; 1.0; 1.2; 1.5; 1.7; 2.0; 2.2; 2.5; 2.7; 3.0)系列，2aBaCu_(2-x)Sn_xO_(4.5) + x (x = 0; 0.2; 0.5; 0.7; 1.0; 1.2; 1.5; 1.7; 2.0)系列和La_3Cu_(3-x)Sn_xO_(7.5) + x (x = 0.5; 1.0; 1.5; 2.0; 2.2; 2.5; 2.7)系列等二十八个新复合氧化物。这三个系列二十八个新复合氧化物直至目前为止，文献上未见过报道。我们通过x-ray粉末衍射图分析了它们的结构，肯定了它们是新的单一化合物，计算了它们的晶胞参数并确定它们的所属晶系。元素化学分析表明，所有这些化合物均可用原始计算配比化学式表示。干湿两种合成方法所合成的结构相同。对于这三个系列二十八个瓣复合氧化物，我们选用LaBa_2-Cu_(3-x)Sn_xO_(6.5) = x (x = 0.5;1.0;1.5;2.0;2.5),LaBaCu_(2-x)Sn_xO_(4.5) = x(x = 0.5; 1.0; 1.5;2.0), La_3Cu_(3-x)Sn_xO_(7.5) + x (x = 0.5; 1.0; 1.5; 2.0; 2.5)等十四个化合物，对它们的低温，高温和高湿下的电阻率和导电类型进行了测试，绘得了它们的电阻率和温度的关系曲线。在一定温度下，一个系列内的化合物电阻率随锡的分子含量增加而增大。La_3Cu_(3-x)Sn_xO_(7.5) = x系统人物的电阻率明显大于其它二个系列相应化合物的电阻率。所有化合物在液氮至室温温区内，基本上呈半导体导电类型。在高温以上温区，当温度升至一定温度时之前，化合物呈本导体导电类型达到一定温度之后，当金属导电类型所有新复合氧化物在高温均属P型半导体。本文还研究了这三个系列化合物和将它们掺入二氧化锡中的气敏性能。结果表明：所有这类化合物和将它们掺入二氧化锡中作为添加剂做成的气敏材料，除LaBa_2Cu_(1.5)Sn_(1.5)O_8掺入SnO_2做成的气敏材料外，在本文实验条件下做成的气敏元件对氧化性和还原性气体均无或只有很差的气敏性。LaBa_2Cu_(1.5)Sn_(1.5)O_8作为添加剂掺入SnO_2中(摩尔比0.2:0.8; 0.1:0.9)所制得的气敏文件对高浓度(1%-10%)的一氧化碳，液化气和煤气具有很好的气敏线性响应，当加热电流为300mA时，酒精，汽油和石油醚等还原性气体基本上无干扰。实验表明当摩尔比为0.1:0.9时，材料的气敏性能最佳，但重现性较差，当摩尔比为0.2:0.8时，气敏性稍低，但重现性较好。本文还合成了La_xBa_(1-x)SnO_3(x = 0; 0.05; 0.10; 0.15, 0.20)系列化合物，并确定了它们的结构和所属晶系。从结构上分析我们认该系列化合物相互之间为置换固溶体。其晶胞参数随镧的加入量增加而减小。该系列均属几型半导体材料。我们利用该系列材料进行了过敏性研究。结果表明。由La_(0.1)Ba_(0.9)SnO_3制得的高热式气敏器件对低浓度酒精(<1000 ppm)有很好的气敏线性响应。在加热电流为250 mA时，基本上排除了煤气，一氧化碳，液化气和汽油等可燃性气体的干扰。但香烟烟雾对器件检测酒精有一定的影响。La_(0.1)Ba_(0.9)SnO_3气敏材料多添加1%而制得的器件，机械强度达到很好的效果，器件对酒精的灵敏度有降低，而响应浓度区间宽度增加近一倍，选择性几乎不变。该材料具有较好的实验重现性。该系列的其它化合物在本实验条件下所制得的器件对可燃性气体的敏感性较差。

AlGaInAs-InPMicrocylinder Lasers Connected With an Output Waveguide

AlGaInAs-InPmicrocylinder lasers connected with an output waveguide are fabricated by planar technology. Room-temperature continuous-wave operation with a threshold current of 8 mA is realized for a microcylinder laser with the radius of 10 mu m and the output waveguide width of 2 mu m. The mode Q-factor of 1.2 x 10(4) is measured from the laser spectrum at the threshold. Coupled mode characteristics are analyzed by 2-D finite-difference time-domain simulation and the analytical solution of whispering-gallery modes. The calculated mode Q-factors of coupled modes are in the same order as the measured value.

PRESSURE-DEPENDENCE OF PHOTOLUMINESCENCE IN IN(X)GA(1-X)AS/AL(Y)GA(1-Y)AS STRAINED QUANTUM-WELLS WITH DIFFERENT WIDTH

A systematic investigation on the photoluminescence (PL) properties of InxGa1-xAs/AlyGa1-xAs (x = 0.15, y = 0, 0.33) strained quantum wells (SQWs) with well widths from 1.7 to 11.0 nm has been performed at 77 K under high pressure up to 40 kbar. The experimental results show that the pressure coefficients of the exciton peaks corresponding to transitions from the first conduction subband to the heavy-hole subband increase from 10.05 meV/kbar of 11.0 nm well to 10.62 meV/kbar of 1.8 nm well for In0.15Ga0.85As/GaAs SQWs. However, the corresponding pressure coefficients slightly decrease from 9.93 meV/kbar of 9.0 nm well to 9.73 meV/kbar of 1.7 nm well for In0.15Ga0.85As/Al0.33Ga0.67As SQWs. Calculations based on the Kronig-Penney model reveal that the increased or decreased barrier heights and the increased effective masses with pressure are the main reasons of the change in the pressure coefficients.

液相外延生长In_xGa_(1-x)As_ySb_(1-y)/GaSb及其性质研究

于2010-11-23批量导入

Al_xGa_(1-x)As_ySb_(1-y)/GaSb的LPE生长与性质研究

其它基金

Magnets for HIRFL-CSR rings

The magnet design, fabrication, and measurement of HIRFL-CSR (Heavy Ion Research Facility in Lanzhou Cooling Storage Ring) are presented. All magnets will be laminated And welded with an armor-coated surface between two big endplates made of sticking glue 0.5 mm-thick sheets. The dipole of CSRm was chosen an H type with an air circle on the pole to improve the field uniformity. The dipole of CSRe was chosen the C type with an air circle and two air slots on the pole to improve the field homogeneity. Its reproducibility of magnet to magnet was adjusted with inserting small laminating pieces before demountable pole ends to reach less than +/- 2 x 10(-4) at optimized field level. CSRm quadrupoles diameter is 170 mm and has two different lengths, and its endplates were made with punching pieces after coating with epoxy glue, there is chamfered directly on the pole ends to reduce 12th-order contribution of field and without the demountable pole ends. CSRe main quadrupoles diameter is 240 mm and has two different lengths, and its endplates were also made with punching pieces coated with epoxy glue, there is also chamfered directly on the pole ends to reduce 12th-order contribution of field like CSRm.