Analysis of mode quality factors for equilateral triangle semiconductor microlasers with rough sidewalls

The eigenmode characteristics for equilateral triangle resonator (ETR) semiconductor microlasers are analysed by the finite-difference time-domain technique and the Pade approximation. The random Gaussian correlation function and sinusoidal function are used to model the side roughness of the ETR. The numerical results show that the roughness can cause the split of the degenerative modes, but the confined modes can still have a high quality factor. For the ETR with a 3 mum side length and the sinusoidal fluctuation, we can have a quality factor of 800 for the fundamental mode in the wavelength of 1500 nm, as the amplitude of roughness is 75 mn.

High-performance 980-nm quantum-well lasers using a hybrid material system of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers grown by metal-organic chemical vapor deposition

We report on the material growth and fabrication of high-performance 980-nm strained quantum-well lasers employing a hybrid material system consisting of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. The use of AlGaAs cladding instead of InGaP provides potential advantages in flexibility of laser design, simple epitaxial growth, and improvement of surface morphology and laser performance. The as-grown InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.95 eV) lasers achieve a low threshold current density of 150 A/cm(2) (at a cavity length of 1500 mu m), internal quantum efficiency of similar to 95%, and low internal loss of 1.8 cm(-1). Both broad-area and ridge-waveguide laser devices are fabricated. For 100-mu m-wide stripe lasers with a cavity length of 800 Irm, a slope efficiency of 1.05 W/A and a characteristic temperature coefficient (T-0) of 230 K are achieved. The lifetime test demonstrates a reliable performance. The comparison with our fabricated InGaAs-InGaAsP(1.6 eV)-AlGaAs(1.87 eV) lasers and Al-free InGaAs-InGaAsP (1.6 eV)-InGaP lasers are also given and discussed. The selective etching between AlGaAs and InGaAsP is successfully used for the formation of a ridge-waveguide structure. For 4-mu m-wide ridge-waveguide laser devices, a maximum output power of 350 mW is achieved. The fundamental mode output power can be up to 190 mW with a slope efficiency as high as 0.94 W/A.

Homoepitaxial growth and characterization of 4H-SiC epilayers by low-pressure hot-wall chemical vapor deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get high quality 4H-SiC epilayers. Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates purchased from Cree is performed at a typical temperature of 1500 degrees C with a pressure of 40 Torr by using SiH4+C2H4+H-2 gas system. The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope, atomic force microscopy (AFM), x-ray diffraction, Raman scattering, and low temperature photoluminescence (LTPL). The background doping of 32 pm-thick sample has been reduced to 2-5 x 10(15) cm(-3). The FWHM of the rocking curve is 9-16 arcsec. Intentional N-doped and B-doped 4H-SiC epilayers are obtained by in-situ doping of NH3 and B2H6, respectively. Schottky barrier diodes with reverse blocking voltage of over 1000 V are achieved preliminarily.

Growth and characterization of 4H-SiC by horizontal hot-wall CVD

4H-SiC layers have been homoepitaxially grown at 1500 degrees C with the use of a horizontal hot-wall chemical vapor deposition (CVD) system, which was built in the author's group. The typical growth rate was 2 mu m/h at a pressure of 40 Torr. The background donor concentration has been reduced to 2.3 x 10(15) cm(-3) during a prolonged growth run. It confirmed the idea that the high background concentration of thin films was caused by the impurities inside the susceptor and thermal insulator The FWHM of x-ray co-rocking curves show 9 similar to 15 aresecs in five different areas of a 32-mu m-thick 4H-SiC epilayer The free exciton peaks dominated in the near-band-edge low-temperature photoluminescence spectrum (LTPL), indicating high crystal quality.

Morphological defects and uniformity issues of 4H-SiC homoepitaxial layers grown on off-oriented (0001)Si faces

The morphological defects and uniformity of 4H-SiC epilayers grown by hot wall CVD at 1500 degrees C on off-oriented (0001) Si faces are characterized by atomic force microscope, Nomarski optical microscopy, and Micro-Raman spectroscopy. Typical morphological defects including triangular defects, wavy steps, round pits, and groove defects are observed in mirror-like SiC epilayers. The preparation of the substrate surface is necessary for the growth of high-quality 4H-SiC epitaxial layers with low-surface defect density under optimized growth conditions. (c) 2006 Elsevier Ltd. All rights reserved.

Homoepitaxial growth and MOS structures of 4H-SiC on off oriented n-type (0001)Si-faces

Homoepitaxial growth of 4H-SiC on off-oriented n-type Si-face (0001) substrates was performed in a home-made hot-wall low pressure chemical vapor deposition (LPCVD) reactor with SiH4 and C2H4 at temperature of 1500 C and pressure of 20 Torr. The surface morphology and intentional in-situ NH3 doping in 4H-SiC epilayers were investigated by using atomic force microscopy (AFM) and secondary ion mass spectroscopy (SIMS). Thermal oxidization of 4H-SiC homoepitaxial layers was conducted in a dry O-2 and H-2 atmosphere at temperature of 1150 C. The oxide was investigated by employing x-ray photoelectron spectroscopy (XPS). 4H-SiC MOS structures were obtained and their C-V characteristics were presented.

Evaluation of thermal radiation dependent performance of GaSb thermophotovoltaic cell based on an analytical absorption coefficient model

Applying the model dielectric function method, we have expressed the absorption coefficient of GaSb analytically at room temperature relating to the contribution of various critical points of its electronic band structure. The calculated absorption spectrum shows good agreement with the reported experimental data obtained by spectral ellipsometry on nominally undoped sample. Based on this analytical absorption spectrum, we have qualitatively evaluated the response of active absorbing layer structure and its photoelectric conversion properties of GaSb thermophotovoltaic device on the perturbation of external thermal radiation induced by the varying radiator temperature or emissivity. Our calculation has demonstrated that desirable thickness to achieve the maximum conversion efficiency should be decreased with the increment of radiator temperature and the performance degradation brought by any structure deviation from its optimal one would be stronger meanwhile. For the popular radiator temperature, no more than 1500 K in a real solar thermophotovoltaic system, and typical doping profile in GaSb cell, a reasonable absorbing layer structure parameter should be controlled within 100-300 nm for the emitter while 3000-5000 nm for the base.

现代化大宾馆采用热泵运行的节能潜力

一、概述随着城市对外开放政策的发展，宾馆现代化设施日益增多。成为城市的耗能大户，新建及改建的大宾馆，装备越来越完善，好多地区能源十分紧张。电力和燃料要优先满足宾馆使用，严重影响到地区工农业生产及人民生活对能源的需要。以一所规模约为1000个客房的现代宾馆为例:通常装有5～8台大型空调制冷机组，装机容量可达1500～2500千瓦。这些机组运行耗电量占全宾馆的50～60%，运行连续时间全年可达6～8个月，由制冷机生产的低温(7～9℃)冷冻水，送至供冷系统，供全宾馆空调使用，制冷机本身消耗的电能连同从制冷冻水

Design and operation of integrated pilot-scale dimethyl ether synthesis system via pyrolysis/gasification of corncob

The integrated pilot-scale dimethyl ether (DME) synthesis system from corncob was demonstrated for modernizing utilization of biomass residues. The raw bio-syngas was obtained by the pyrolyzer/gasifier at the yield rate of 40-45 Nm(3)/h. The content of tar in the raw bio-syngas was decreased to less than 20 mg/Nm(3) by high temperature gasification of the pyrolysates under O-2-rich air. More than 70% CO2 in the raw bio-syngas was removed by pressure-swing adsorption unit (PSA). The bio-syngas (H-2/CO approximate to 1) was catalytically converted to DME in the fixed-bed tubular reactor directly over Cu/Zn/Al/HZSM-5 catalysts. CO conversion and space-time yield of DME were in the range of 82.0-73.6% and 124.3-203.8 kg/m(cat)(3)/h, respectively, with a similar DME selectivity when gas hourly space velocity (GHSV, volumetric flow rate of syngas at STP divided by the volume of catalyst) increased from 650 h(-1) to 1500 h(-1) at 260 degrees C and 4.3 MPa. And the selectivity to methanol and C-2(+) products was less than 0.65% under typical synthesis condition. The thermal energy conversion efficiency was ca. 32.0% and about 16.4% carbon in dried corncob was essentially converted to DME with the production cost of ca. (sic) 3737/ton DME. Cu (111) was assumed to be the active phase for DME synthesis, confirmed by X-ray diffraction (XRD) characterization.

Methane hydrate growth velocity in seepage system of Qiongdongnan Basin, South China Sea

The occurrences of diapirs, gas-filled zones and gas plumes in seawater in Qiongdongnan Basin of South China Sea indicate that there may exist seepage system gas-hydrate reservoirs. Assuming there has a methane venting zone of 1500 m in diameter, and the methane flux is 1000 kmol/a, and the temperature of methane hydrate-bearing sediments ranges from 3 degrees C to 20 degrees C, then according to the hydrate film growth theory, by numerical simulation, this paper computes the temperatures and velocities in 0 mbsf, 100 mbsf, 200 mbsf, 425 mbsf over discrete length, and gives the change charts. The results show that the cementation velocity in sediments matrix of methane hydrate is about 0.2 nm/s, and the seepage system will evolve into diffusion system over probably 35000 years. Meanwhile, the methane hydrate growth velocity in leakage system is 20 similar to 40 times faster than in diffusion system.

The design and operation of a new clapboard-type internal circulating fluidized-bed gasifier

The design and operation of a new clapboard-type internal circulating fluidized-bed gasifier is proposed in this article. By arranging the clapboard in the bed, the gasifier is thus divided into two regions, which are characterized by different fluidization velocities. The bed structure is designed so that it can guide the circulating flow passing through the two regions, and therefore the feedstock particles entrained in the flow experience longer residence time. The experimental results based on the present new design, operating in the temperature range of 790 degrees C-850 degrees C, indicate that the gas yield is from 1.6-1.9 Nm(3)/kg feedstock, the gas enthalpies are 5,345 kJ/Nm(3) for wood chip and 4,875 kJ/m(3) for rice husk, and a gasification efficiency up to 75% can be obtained.

聚（ε-己内酯）泡沫塑料制备与性能研究

随着人们环保意识的普遍提高，可生物降解材料已经成为了世界范围的研究热点。开展可生物降解高分子泡沫塑料的结构与性能的研究，对以可生物降解的高分子泡沫塑料替代不能生物降解的泡沫塑料，遏制白色污染，保护生态环境，具有重要的科学价值和社会意义。本工作选用聚（ε-己内醋）（PCL）为原料，通过辐射方法引发PCL交联，提高其熔体粘度和强度；以AC为发泡剂，制备PCL泡沫材料：添加无机纳米粒子-碳酸钙，进一步提高PCL的发泡倍率。研究辐射剂量、凝胶含量、分子量、AC发泡剂含量、碳酸钙含量等因素对制备泡沫塑料的影响，优化组合，获得PCL泡沫材料。主要研究结果如下：1．采用辐照交联的方法实现了PCL的交联，凝胶含量最高可达到41％；2．交联后的PCL热稳定性略有下降，结晶性能基本没有变化。但是，抗张性能变化很大，弹性模量提高（260MPa-430MPa），断裂伸长率下降（1500％-30％）。由此推测，提高了PCL的熔体强度；3．制备出了PCL泡沫塑料，发泡倍率可控制在2-12范围内。其中，发泡倍率与发泡剂含量、PCL分子量关系密切。当辐照计量大于5Mrad后，辐照计量对发泡倍率影响不大，但是，对泡孔的结构影响很大，即辐照剂量大，得到的泡孔直径小；4．体系中添加CoCO_3使得PCL的发泡倍率进一步提高，最高可达到15倍，并且使泡孔数量增加，体积减小。添加30wt％碳酸钙，PCL泡沫塑料的孔径为147μm，单位体积泡孔数为29.6*10~8cell/cm~3，壁厚4.48μm。

高分子在化学和物理受限环境中结晶行为的研究

高分子的受限结晶是高分子科学中的一个重要研究方向。本论文以受限高分子为研究对象，系统地研究了高分子在化学交联点间的受限（一维）和超薄膜中的物理空间受限（二维）条件下的结晶熔融行为。 以聚乙二醇的交联网络为研究对象，研究了不同分子量的聚乙二醇在化学交联网络中的结晶熔融行为。结果表明，在聚乙二醇链结构中交联点的存在使聚合物的熔点和结晶度降低。当交联点间的分子量减小到1000时，高分子不能结晶。结果表明在交联网络受限下的结晶所需交联点间的最低分子量应介于1000-1500，低于此分子量高分子不能结晶。 以聚卜己内酷为研究对象，系统地研究了聚ε-已内酯在物理受限空间，即在薄膜、超薄膜中的结晶与熔融行为。结果表明，聚卜己内醋的结晶形态与薄膜的厚度有关。当薄膜的厚度大2Rg（Rg为均方回转半径）时，高分子结晶形态呈现球晶；当厚度介于Rg-2Rg之间时，高分子结晶生成枝蔓或树枝状结构，当厚度小于Rg时，其结晶形态为分形结构。熔融过程并不能完全破坏其形态。这些都可归因于表面效应、基底效应和薄膜受限效应之间的复杂的相互作用。此外，本文还讨论了结晶温度、基底、分子量等对高分子结晶形态的影响。最后对树枝晶的生长进行了原位跟踪。结果表明，高分子在薄膜中的结晶是一个扩散控制的动力学过程，同时也是一种远离平衡态的形态生成过程。