A thick window pAl0.7Ga0.3As-pGaAs-nGaAs concentrator Solar Cell

Thick window pAl_0.7Ga_0.3As-pGaAs-nGaAs solar cells are reported being grown by forced cooling LPE. Device evaluation shows an 18% maximum conversion efficiency at room temperature. A method for calculating cell conversion efficiency upon knowledge of internal collection efficiency, open circuit voltage and short circuit current is also devised.     

The pAl0.7Ga0.3As-pGaAs-nGaAs concentrator cell with electrolytical contacts

The technological procedure involved in making p-Al_0.7Ga_0.3As-p-GaAs-n-GaAs concentrator solar cells by forced cooling LPE is discussed. Electrical contacts were electrochemically deposited from acid baths of Au and Ni, followed by annealing. 1.4 A/cm² short current densities and 1 V open circuit voltages were measured under 7 W/cm² incident radiation.     

Electrical Properties of Praseodymium-doped GaAs and Al0.3Ga0.7As Epilayers

Praseodymium-doped GaAs and Al_0.3Ga_0.7As epilayers grown on Semi-Insulating (SI) GaAs substrates by Liquid Phase Epitaxy (LPE) were first studied in this present work. Measurement techniques, such as microscopic observation, X-ray diffraction, Secondary Ion Mass Spectroscopy (SIMS), and Hall measurement were employed. Layers doped with Pr resulted in a mirror-like surface, except several high Pr-doped layers having droplet surfaces. Hall measurements reveal that the grown layers contained p-type layers, carrier concentrations from 6.3 × 10¹⁵ to 1.2 × 10¹⁶ cm⁻³, and from 6.3 × 10¹⁵ to 3.5 × 10¹⁶ cm⁻³ for Pr-doped GaAs and Al_0.3Ga_0.7As epilayers, respectively. Although p-type conduction exists, in the light of electrical features, doping of Pr into the GaAs and Al_0.3Ga_0.7As growth melts, is still considered to exhibit gettering properties rather than to become a new acceptor itself. Additional photoluminescence examinations were taken. Their results also indicate that Pr-doped layers produce no new emission lines and support the electrical observations.     

Electrophysical characteristics and structural parameters of metamorphic HEMT nanoheterostructures In0.7Al0.3As/In0.7Ga0.3As/In0.7Al0.3As containing superlattices with different numbers of periods in the metamorphic buffer

The results of studying the electrophysical characteristics and structural parameters of metamorphic In_0.7Al_0.3As/In_0.7Ga_0.3As/In_0.7Al_0.3As HEMT nanoheterostructures epitaxially grown on GaAs (100) substrates have been presented. A linear metamorphic buffer with inserted unbalanced superlattices characterized by different numbers of periods is used. Transmission electron microscopy has shown that an increase in the number of superlattice periods from 5 to 30 promotes the improvement of the crystal structure. In this case, the electrophysical parameters of metamorphic HEMT nanoheterostructures are also significantly improved.     

Structural and electrical properties of CuIn0.7Ga0.3Se2 epitaxial layers on GaAs substrates

Epitaxial layers of CuIn_0.7Ga_0.3Se₂ could be prepared by flash evaporation onto (111)A-oriented GaAs substrates in the substrate temperature range T_sub = 745 … 870 K. At T_sub = 745 … 820 K the films had the chalcopyrite structure, at T_sub = 820 … 845 K an additional pseudohexagonal phase was found. Indications to the presence of a sphalerite phase were found at high substrate temperatures. Films grown at T_sub ≦ 750 K were always n-type conducting and showed a largely pronounced impurity band conduction effect. At T_sub ≧ 860 K the films were always p-type conducting and two acceptor states with ionization energies of some 10⁻³ eV and of 125 … 140 meV were found.     

Defects and stresses in MBE-grown GaN and Al0.3Ga0.7N layers doped by silicon using silane

The electric and structural characteristics of silicon-doped GaN and Al_0.3Ga_0.7N layers grown by molecular beam epitaxy (MBE) using silane have been analyzed by the Hall effect, Raman spectroscopy, and high-resolution X-ray diffractometry. It is established that the electron concentration linearly increases up to n = 4 × 10²⁰ cm^?3 with an increase in the silane flow rate for GaN:Si, whereas the corresponding dependence for Al_0.3Ga_0.7N:Si is sublinear and the maximum electron concentration is found to be n = 4 × 10¹⁹ cm^?3. X-ray measurements of sample macrobending indicate a decrease in biaxial compressive stress with an increase in the electron concentration in both GaN:Si and Al_0.3Ga_0.7N:Si layers. The parameters of the dislocation structure, estimated from the measured broadenings of X-ray reflections, are analyzed.     

Crystal growth and characterization of Rb0.3K0.7TiOPO4

Single crystal growth and characterization of Rb_0.3K_0.7TiOPO₄ are reported. After improving the technological procedures of crystal growth, high-quality large single crystals were obtained. The refractive indices, pyroelectric coefficient, dielectric, piezoelectric, elastic, thermoelastic and elastooptic constants, SHG efficiency and damage threshold were measured.     

Ga源温度对共蒸发三步法制备Cu(In,Ga)Se2太阳电池的影响

利用共蒸发三步法制备了Cu(In,Ga)Se2(CIGS)薄膜,并通过调整制备工艺中的一、三步的金属镓(Ga)的温度,改变Ga含量的梯度分布,研究不同梯度分布对CIGS薄膜及电池性能的影响.从而优化了电池带隙梯度分布,使电池的开路电压Voc在提高的同时,最大程度的减小了Jsc的损失.优化后薄膜表面的结晶情况得到改善,电池的结界面和二极管特性也得到相应的提高.量子效率测试发现,优化后的CIGS太阳电池在较长波段中(520～1100nm)的光子吸收损失大大减小.     

On the structure of the molten mixture Ag(I0.3Br0.7)

We present neutron diffraction measurements of the total structure factor of the molten salt mixture Ag(I_0.3Br_0.7) at 650 °C, measured by using the high intensity total scattering time-of-flight spectrometer, HIT-II, at the spallation neutron source of the Neutron Science Laboratory in the High Energy Accelerator Research Organization of Japan. We have compared the experimental data with molecular dynamics simulations using Vashishta–Rahman type potentials. Within the known constraints of pairwise rigid ion potentials, the results of the simulations are in fair agreement with experiment. We also present results using a linear combination of the experimental and molecular dynamics simulations of the structure factors of the AgI and AgBr melts. The latter are in somewhat better agreement with experiment.     

Transport behavior of yttrium substituted polycrystalline La0.7Pb0.3MnO3

The transport properties in La_0.7?xY_xPb_0.3MnO₃ (0.0 ? x ? 0.2) is investigated. The substitution of La³⁺ ions by smaller nonmagnetic Y³⁺ leads to greater spin disorder and induces variations in the magnetotransport behavior. From resistivity versus temperature curves a metal–insulator transition phenomenon is observed at the transition temperature, T_P, decreases as the Y content increases. The resistivity is well fitted using the equation ρ(T) = ρ_nexp[(T¹/T)ⁿ] with n = 1/4 and n = 1/2 at high and intermediate temperatures, respectively. The characteristic temperature T¹ varies with Y content in a manner consistent with the localization model of variable range hopping. Below T_P, resistivity varies as a function of power law contributions, ρ = ρ₀ + ρ₂T² + ρ_5/2T^5/2, corresponding to the electron scattering processes in the ferromagnetic phase.     

AgGa0.7In0.3Se2晶体热膨胀行为研究

采用一种新的定向方法,快速定出了AgGa0.7In03Se2晶体c轴方向,制备得到[001]、[100]方向的块状样品;采用德国B(a)hr公司的WinTA 100热膨胀仪对其进行测试,分别获得了晶体沿c轴、a轴方向的热膨胀系数,分析了它们随温度变化的规律以及晶体出现反常热膨胀的机制;计算出晶体的体热膨胀系数和各向异性因子,分析讨论了晶体非轴向热膨胀系数在不同温度下随cos2φ的变化规律.     

Electrical and magnetotransport properties of La0.7Sr0.3MnO3/TiO2 composites

The composite samples with nominal compositions of (1‐x) La_0.7Sr_0.3MnO₃ + x TiO₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were synthesized via solid state reaction process. The X‐ray diffraction and scanning electronic microscopy observations reveal no reaction between La_0.7Sr_0.3MnO₃ (LSMO) and TiO₂ phases. Temperature dependence resistivity measurements show that TiO₂ phase shifts the metal‐insulator transition temperature (T_p) towards lower temperature and increases the resistivity. Moreover, the magnetization of the composite samples decreases with TiO₂ content. An enhancement in magnetoresistance is observed in the composite samples with x = 0.05 and x = 0.10 at low magnetic fields, which is encouraging for potential application of magnetoresistive materials at low field. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

热处理对Ni0.7Zn0.3O薄膜结构及缺陷荧光特性的影响

采用脉冲激光沉积法在Si(100)衬底上制备了Ni0.7Zn0.3O薄膜,通过热处理改变薄膜的缺陷状态,并利用X射线衍射仪、扫描电子显微镜和荧光光谱仪表征薄膜的晶体结构、表面形貌和缺陷发光特性.结果表明:沉积态薄膜为立方结构的Ni0.7Zn0.3O单相,且沿着(200)面高度取向生长.经过热处理后,薄膜形成ZnO和Ni0.7Zn0.3O两相共存的镶嵌结构.样品具有非常丰富的室温荧光光谱,其发光峰主要来自Ni0.7Zn0.3O的缺陷能级跃迁,多缺陷能级导致了多发光峰的荧光光谱.热处理引起薄膜中缺陷的种类和浓度发生变化,严重影响其发光特性.     

La2(Zr0.7Ce0.3)2O7纳米粉体的制备与表征

采用化学沉淀法制备了高性能热障涂层用La2(Zr0.7Ce0.3)2O7陶瓷粉体.通过TG-DSC、XRD、SEM及TEM对前驱体的烧结温度、粉体物相及微观结构进行了分析.结果表明:制备的粉体为纳米级,且颗粒分布均匀,粒径大约30 ～ 50 nm;La2(Zr0.7Ce0.3)2O7是由烧绿石结构的La2Zr2O7固溶体和萤石结构的La2Ce2O7固溶体复合组成.     

烧成温度对La0.7Ca0.3CrO3/Al2O3导电陶瓷微滤膜支撑体结构与性能的影响

采用高温固相反应烧结法制备La0.7Ca0.3CrO3(LCC)/Al2O3导电陶瓷微滤膜支撑体.研究了烧成温度对制备的LCC/Al2O3支撑体样品的物相组成、微观结构、烧成收缩、孔隙率和孔径分布、电导率、抗弯强度、渗透通量及耐腐蚀性能等的影响.结果表明,高温烧成过程中LCC与Al2O3发生复杂的固相反应,样品主晶相为菱形结构La07Ca0.3Cr1-xAlxO3,并生成了少量LaAl11O18和CaCr2O4等.烧成温度从1350℃提高到1600℃时,样品的烧结程度、电导率、抗弯强度和耐酸腐蚀性能明显提高,而孔隙率明显减小.样品的平均孔径和纯水渗透通量随烧成温度提高,表现出先增大后减小的变化趋势.在1550℃时保温2h烧成制备的LCC/Al2O3支撑体,具有高的孔隙率(43.4;)和抗弯强度(36.9 MPa),其平均孔径(d50)为1.02 μm、纯水通量为2.24 m3/m2·h·bar、电导率为0.11 S/m,且具有良好的耐腐蚀性能.     

Li2CO3对0.7CaTiO3-0.3SmAlO3陶瓷性能的影响

采用固相反应法,以0.7CaTiO3-0.3SmAlO3 (CSTA)为基础配方,研究了Li2CO3对CSTA微波介质陶瓷性能的影响.结果表明:添加适量的Li2CO3可有效的降低CSTA的烧结温度,由1500℃降低到1380℃.XRD分析表明:Li2CO3的引入未改变陶瓷的的晶相组成.SEM分析表明,添加Li2CO3会抑制晶粒长大,当添加0.lwt;时,晶粒尺寸小,分布均匀;随着添加量的增加,玻璃相增加,部分晶粒长大,分布不均匀,从而降低品质因数.添加0.lwt;的Li2CO3的CSTA陶瓷在1380 ℃烧结时获得最佳介电性能:εr=45.09,Q·f=61600 GHz (f=6.417 GHz),тf=+7.54×10-6/℃.     

ZnO掺杂对0.7CaTiO3-0.3NdAlO3微波介质陶瓷低温烧结及介电性能的影响

采用固相法制备0.7CaTiO3-0.3NdAlO3微波介质陶瓷,研究添加不同含量纳米ZnO对其烧结特性和微波介电性能的影响.结果表明,掺入ZnO烧结温度降低了100℃,随着ZnO掺量增加,样品介电常数εr和谐振频率温度系数τf减小,品质因数(Q×f)先增大后减小.掺入1.5wt;的ZnO在1350℃烧结4h时性能最佳:εr=36.50,Q×f=23785 GHz,τf=-2.47×10-6/℃.     

高性能Ag/La0.7Mg0.3MnO3/p+-Si阻变器件的研究

采用溶胶-凝胶工艺在p型单晶硅衬底上制备了La0.7Mg0.3MnO3薄膜,对薄膜的微观结构及Ag/La0.7Mg0.3MnO3/p+-Si器件的电致阻变性能进行了研究.结果表明:La0.7Mg0.3MnO3薄膜在经过700℃退火2h后为单一的钙钛矿结构,沿(112)晶向择优生长,薄膜致密平整;Ag/La0.7Mg0.3MnO3/p+-Si阻变器件具有典型的双极型阻变特性,具有非常高的电阻开关比,其高阻态(HRS)与低阻态(LRS)的比值高于105,以及较佳的耐疲劳性能,器件在1000次循环后高、低阻态比值没有明显变化;器件在高阻态(HRS)时的导电机制为Schotty势垒发射效应,低阻态(LRS)导电机制为导电细丝机制.     

Electrical properties of SrBi2(Nb0.7V0.3)2O9−δ in the SrO–Bi2O3–0.7Nb2O5–0.3V2O5–Li2B4O7 glass system

Glasses in the system (100 − x)Li₂B₄O₇–x(SrO–Bi₂O₃–0.7Nb₂O₅–0.3V₂O₅) (where x = 10, 30 and 50, in molar ratio) were fabricated via melt quenching technique. The compositional dependence of the glass transition (T_g) and crystallization (T_cr) temperatures was determined by differential thermal analysis. The as-quenched glasses on heat-treatment at 783 K for 6 h yielded monophasic crystalline strontium bismuth niobate doped with vanadium (SrBi₂(Nb_0.7V_0.3)₂O_9−δ (SBVN)) in lithium borate (Li₂B₄O₇ (LBO)) glass matrix. The formation of nanocrystalline layered perovskite SBVN phase was preceded by the fluorite phase as established by both the X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants for both the as-quenched glass and glass–nanocrystal composite increased with increasing temperature in the 300–873 K range, exhibiting a maximum in the vicinity of the crystallization temperature of the host glass matrix. The electrical behavior of the glasses and glass–nanocrystal composites was characterized using impedance spectroscopy.