Análisis dieléctrico del compuesto La(1-x)Ca(x)MnO3 [x=0.2]

Lan honen helburua La1-x Cax MnO3 [x ~ 0.2] (perovskiten familiakoa) laginaren azterketan oinarritzen da. "High resolution dielectric analyzer" tresnari esker permitibitate dielektrikoa neurtuko da eta honen bitartez erresistentzia eta eroankortasun elektrikoa. Azterketa hau [10-2, 107] Hz maiztasun-tarte batean eta tenperatura desberdinetan (150K, 170K, 190K, 210K, 230K, 300K) burutuko da, ondoren materialak magnitude hauen bariazioekiko duen erantzuna aztertuz.

Comparison of laser performances of 5at.% Yb : Gd2xY2(1-x)SiO5 crystals between different cutting directions

We investigate the laser actions of 5at.% Yb:Gd2xY2(1-x)SiO5 (Yb:GYSO; x = 0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9 W. In contrast, the sample cut parallel reaches only 1.65 W at 1044 nm with a slope elLiciency of 33.76% with absorbed pump power of 7.99 W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68 nm to 1084.82 nm.

Schottky barriers on compound semiconductors: I. HgSe highly electronegative contacts. II. Au Schottky barriers on n-Ga_(1-x)Al_xAs

I. HgSe is deposited on various semiconductors, forming a semimetal/semiconductor "Schottky barrier" structure. Polycrystalline, evaporated HgSe produces larger Schottky barrier heights on n-type semiconductors than does Au, the most electronegative of the elemental metals. The barrier heights are about 0.5 eV greater than those of Au on ionic semiconductors such as ZnS, and 0.1 to 0.2 eV greater for more covalently bonded semiconductors. A novel structure,which is both a lattice matched heterostructure and a Schottky barrier, is fabricated by epitaxial growth of HgSe on CdSe using hydrogen transport CVD. The Schottky barrier height for this structure is 0.73 ± 0.02 eV, as measured by the photoresponse method. This uncertainty is unusually small; and the magnitude is greater by about a quarter volt than is achievable with Au, in qualitative agreement with ionization potential arguments.

II . The Schottky barrier height of Au on chemically etched n-Ga_1-x Al_xAs was measured as a function of x. As x increases, the barrier height rises to a value of about 1.2 eV at x ≈ 0.45 , then decreases to about 1.0 eV as x approaches 0.83. The barrier height deviates in a linear way from the value predicted by the "common anion" rule as the AlAs mole fraction increases. This behavior is related to chemical reactivity of the Ga_1-x Al_xAs surface.

1 X N dynamic optical coupler based on Dammann gratings

We present two novel 1XN dynamic optical couplers that are based on Dammann gratings to achieve dynamic optical coupled technology. One is presented by employing a specially designed Dammann grating that consists of the Dammann-grating area and the blank area. The other is developed by using two complementary even-numbered Dammann gratings. The couplers can achieve the function conversion between a beam splitter and a combiner according to the modulation of the gratings. We have experimentally demonstrated 1X8 dynamic optical couplers at the wavelength of 1550 nm. The experimental results and the analyses are reported in detail.

Localização em poço quântico de Ga_(1-x)Al_(x)AsGaAs com campo magnético inclinado intenso

Nesta dissertação, apresentamos resultados da análise de um gás de elétrons bidimensional, confinado em um poço quântico parabólico de Ga_(1-x)Al_(x)As com campo magnético aplicado inclinado e intenso. Mostramos uma solução analítica exata para o caso de um gás de elétrons não interagente e provamos que o fator de Landé efetivo g*, que neste caso varia com a posição devido à própria variação da concentração de Al na liga GaAlAs, também contribui com um termo parabólico nas frequências normais, tornando-as dependente do spin. O termo normal do splitting Zeeman aparece, no entanto, com um fator g dado por aquele do GaAs. Indo além desse tratamento, incluímos um campo elétrico externo, aplicado paralelamente a direção de crescimento, de modo a modular a distribuição de cargas dentro do poço, e com isso controlar externamente os efeitos dos cruzamentos dos níveis. Calculamos numericamente os níveis de energia no poço parabólico quântico, variando o campo magnético aplicado e a inclinação do campo.

1 x 4 Ge-on-SOI PIN Photodetector Array for Parallel Optical Interconnects

High-quality Ge film was epitaxially grown on silicon on insulator using the ultrahigh vacuum chemical vapor deposition. In this paper, we demonstrated that the efficient 1 4 germanium-on-silicon p-i-n photodetector arrays with 1.0 mu m Ge film had a responsivity as high as 0.65 A/W at 1.31 mu m and 0.32 A/W at 1.55 mu m, respectively. The dark current density was about 0.75 mA/cm(2) at 0 V and 13.9 mA/cm(2) at 1.0 V reverse bias. The detectors with a diameter of 25 mu m were measured at 1550 nm incident light under 0 V bias, and the result showed that the 3-dB bandwidth is 2.48 GHz. At a reverse bias of 3 V, the bandwidth is about 13.3 GHz. The four devices showed a good consistency.

Dyakonov-Perel spin relaxation in InSb/AlxIn(1-x)Sb quantum wells

We investigate theoretically the Dyakonov-Perel spin relaxation time by solving the eight-band Kane model and Poisson equation self-consistently. Our results show distinct behavior with the single-band model due to the anomalous spin-orbit interactions in narrow band-gap semiconductors, and agree well with the experiment values reported in recent experiment [K. L. Litvinenko et al., New J. Phys. 8, 49 (2006)]. We find a strong resonant enhancement of the spin relaxation time appears for spin align along [1 (1) over bar0] at a certain electron density at 4 K. This resonant peak is smeared out with increasing the temperature.

Gal(1-x)Mn(1-x)Sb grown on GaSb with mass-analyzed low-energy dual ion beam deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed that the Mn ions were successfully implanted into GaSb substrate. Clear double-crystal X-ray diffraction patterns of the Ga1-xMnxSb samples indicate that the Ga1-xMnxSb epilayers have the zinc-blende structure without detectable second phase. Magnetic hysteresis-loop of the Ga1-xMnxSb epilayers were obtained at room temperature (293 K) with alternating gradient magnetometry. (c) 2005 Elsevier B.V. All rights reserved.

Growth and properties of magnetron cosputtering grown Mn(x)Ge(1-x)on Si(001)

We have grown MnxGe1-x films (x=0, 0.06, 0.1) on Si (001) substrates by magnetron cosputtering, and have explored the resulting structural, morphological, electrical and magnetic properties. X-ray diffraction results show there is no secondary phase except Ge in the Mn0.06Ge0.94 film while new phase appears in the Mn0.1Ge0.9 film. Nanocrystals are formed in the Mn0.06Ge0.94 film, determined by field-emission scanning electron microscopy. Hall measurement indicates that the Mn0.06Ge0.94 film is p-type semiconductor and hole carrier concentration is 6.07 X 10(19) cm(-3) while the MnxGe1-x films with x=0 has n-type carriers. The field dependence of magnetization was measured using alternating gradient magnetometer, and it has been indicated that the Mn0.06Ge0.94 film is ferromagnetic at room temperature. (c) 2005 Elsevier Ltd. All rights reserved.

Pockels effect in GaN/Al-x,Gal(1-x)N superlattice with different quantum structures - art. no. 69841G

The linear electro-optic (Pockels) effect of wurtzite gallium nitride (GaN) films and six-period GaN/AlxGa1-xN superlattices with different quantum structures were demonstrated by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55 mu m. The samples were prepared on (0001) sapphire substrate by low-temperature metalorganic chemical vapor deposition (MOCVD). The measured coefficients of the GaN/AlxGa1-xN superlattices are much larger than those of bulk material. Taking advantage of the strong field localization due to resonances, GaN/AlxGa1-xN SL can be proposed to engineer the nonlinear responses.

液结Hg_(1-x)CaxTe太阳能电池的研究

多晶富镉HerxCdsoTe的电阻率较低，禁带宽度可调，是一种很有希望的半导体光电转换材料。本论文通过对Hg_(1-x)CdxTe(MCT)电沉积的研究，找出了多晶富镉MCT电况积的最佳条件，并对它的结构，组份以及在多硫体系溶液的光电化学性能进行了研究，观察到良好的光响应，在此基础上，进一步深入地研究了不同X值的系列MCT电极的结构，性能。结果表明，不同X值的系列MCT具有相同的闪锌矿型晶体结构，多晶晶粒大小，分布，形态等均没有明显的变化。但随着1－X值的增大，MCT的电导率增高，在多硫电解液中的短路光电流大大上升，但开路光电压却有所下降，这与φ_(fb)随1－X的升高而正移这一实验事实是一致的。即开路光电压的下降是由φ_(fb)的正移，由光谱响应实验得到的Eg值表明：当MCT中的汞含量增大（1-X值升高），禁带宽度下降.经分析，导致Eg变窄的因素在于Ec位置的下降，价带Ev的位置基本保持不变。过高的表面态密度和施主掺杂浓度，大大降低了MCT电极在多硫体系溶液中的Voc,Isc,η,FF。本实验中，未经任何处理MCT沉积膜在多硫电解液中的Voc可达300mV, Isc为3.55mAcm~(-2)，η达0.43%.对MCT／多硫体系在光照下的稳定性进行了热力学分析，表明此体系易于分解，不是稳定体系，实验结果证实了这一点。为了解决以上存在的问题，本论文分别探索了能够影响电极性能的几个因素。MCT的退火处理能够增大多晶晶粒，减少晶粒间界，使Isc大大提高。采用Ni或650 ℃热处理后的Ti作基底呈现出较好的光活性，它的短路光流Isc。开路光电压Voc等比使用经10％HF浸刻的Ti作基底要提高数倍。与多硫体系相比，MCT电极在Fe(CN)_6~(4-)/Fe(CN)_6~(3-)体系中的Voc, Isc提高近二倍，但填充因子F，F未能得到改善。单晶HgIn_2S_4是有明显的n型半导体特征，由光谱响应实验确定出它的禁带宽度为2.0eV，与太阳光谱匹配差。在光极化特性测量中，暗态扫描与光刻至关得要，它能使电极在多硫体系中的光电流提高十多倍。在这种体系HgIn_2S_4的功率效率η=0.1%。稳定性实验表明单晶HgIn_2S_4在多硫体系中的光腐蚀小，光电流稳定。

钙钛石型复合氧化物La_xSr_(1-x)M_yM'_(1-y)O_3(M, M' = Mn, Fe, Co)的固体物理化学性质和催化性能的研究

钙钛石型复合氧化物由于具有许多独特的物理化学性质，如多种类型的磁性和导电性、对多种物理和化学因素的敏感性、高温下的稳定性和结构的明确易调性等长期以来一直受到固体物理、固体化学和催化科技工作者重视，本文第一部分详细总结了文献中有关这类氧化物的结构、电子状态、电磁性质、表面吸附性能、稳定性以及反应机理和催化性能等方面的重要结果。第二部分为催化剂的制备和表征方法。第三部分针对文献中研究较少的B位取代钙钛石型氧化物，系统研究了系列化合物LaM_yM'_(1-y)O_a (M, M' = Mn, Fe, Co)的固体物理化学性质和对NH3和CO氧化反应的催化性能，讨论了它们之间的关系。1. 催化剂的制备、晶体结构与光谱性质。2. LaM_yM'_(1-y)O_3(M、M' = Mn、Fe、Co)r的氧化还原性质和稳定性。3. 过渡金属离子的状态及其之间的相互作用。4. 催化剂中氧的形态。5. 氨氧化性能与固体物化性质之间的关系。6. 一氧化碳氧化与固体物化性质之间的关系。

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.

GaAs/Al_xGa-(1-x)As球形量子点中的电子结构

详细讨论了GaAs/Al_xGa_(1-x)As球形量子点内的单电子束缚能级随量子点半径、Al组分以及外电场的变化规律,并计算了考虑量子点内外电子有效质量不同后对电子能级的修正.另外,用解析和平面波展开两种方法对球形量子点内的电子能级进行了计算,并对计算结果做了比较,发现它们符合的很好.结论和方法为量子点的研究和应用提供了有益的信息和指导.