Electronic defects in LaAlO3

We present calculations of the energy levels of the oxygen vacancy, the Al_La antisite and the oxygen interstitial defects in LaAlO₃ using density functional methods that do not need an empirical bandgap correction. The levels are aligned to those of the Si channel using the known band offsets. The oxygen vacancy gives an energy level near the LaAlO₃ conduction band and above the Si gap. It is identified as the main electron trap and a cause of instability. There is only one vacancy level in the gap, because the higher second level lies within the La conduction band. The Al_La antisite gives a state near midgap, neutral when empty, which would be an important trap, with no counterpart in HfO₂.     

High-Q LaAlO3 dielectric resonator shielded byYBCO-films

We have investigated a dielectric resonator consisting of a single crystalline LaAlO₃-cylinder shielded by a cylindrically shaped copper cavity with endplates made from epitaxial films of YBa₂Cu₃O₇ or niobium. For YBa₂ Cu₃O₇ films unloaded quality factors Q₀ of 4.5·10⁵ at 10 K and 1.3·10⁵ at 77 K were achieved at 11.6 GHz using a compact shielding cavity with a diameter of 15 mm and a height of 3.8 mm. The loss contributions of the dielectric resonator, the normal conducting cylinder wall, and the superconducting endplates, with one of them being separated by a small distance h from the dielectric cylinder, were calculated by modeling the electromagnetic fields of the TE_0νμ-modes. The dielectric loss tangent of the LaAlO ₃-cylinders was found to be 10^-6 at 4.3 K and f=11.6 GHz and to increase slightly with temperature. Moreover, the calculations indicate the tunability of the resonance frequency by changing h over a range of 1 GHz without significant degradation of Q ₀. These resonators are considered to be useful devices for stable oscillators and narrowband filters     

Dielectric properties of single crystals of Al2O3, LaAlO3, NdGaO3, SrTiO3, and MgOat cryogenic temperatures

A dielectric resonator technique has been used for measurements of the permittivity and dielectric loss tangent of single-crystal dielectric substrates in the temperature range 20-300 K at microwave frequencies. Application of superconducting films made it possible to determine dielectric loss tangents of about 5×10^-7 at 20 K. Two permittivity tensor components for uniaxially anisotropic samples were measured. Generally, single-crystal samples made of the same material by different manufacturers or by different processes save significantly different losses, although they have essentially the same permittivities. The permittivity of one crystalline ferroelectric substrate, SrTiO₃, strongly depends on temperature. This temperature dependence can affect the performance of ferroelectric thin-film microwave devices, such as electronically tunable phase shifters, mixers, delay lines and filters     

An HTS narrow bandwidth coplanar shunt inductively coupledmicrowave bandpass filter on LaAlO3

Coplanar waveguide bandpass filters with shunt inductively coupled resonators using high-temperature superconductors (HTS's) on LaAlO₃ substrates were developed for high packing density, narrow bandwidth, and low power applications. The computer-aided design and measurements on resonators to test weak end-coupling are described in this paper. A coplanar three-pole Chebychev bandpass filter with 1.8% 3-dB bandwidth at 10 GHz and 1.3-dB insertion loss at 77 K was fabricated and measured. The maximum superconducting current density of the filter is evaluated     

使用Na_2CO_3/NaHCO_3体系进行单晶硅制绒

通过单晶硅表面制绒可以降低太阳能电池面板对光的反射率进而提高电池的转化效率。利用Na2CO3、NaHCO3和Na2CO3/NaHCO3溶液进行了单晶硅表面制绒,并利用扫描电子显微镜和紫外/可见光光度计对所得绒面的形貌及反色率分别进行了分析。研究了溶液浓度、溶液组成及反应时间等因素对所制单晶硅绒面反射率的影响。结果表明:在Na2CO3:NaHCO3质量比为10:1,反应温度为85℃,反应时间为10 min时,可获得反射率为15.22%的绒面。     

Dielectric tunable properties of (Ba1−xSrx)TiO3 thin films on LaAlO3 substrate

(Ba_1−xSr_x)TiO₃ (1−x=0.8, 0.7, 0.6 and 0.5) thin films were prepared on (0 0 1) LaAlO₃ substrates by sol–gel method. The films were found to be crystallized in preferential (0 0 1) orientation after post-deposition annealing at 750°C for 1.5 h and 1100°C for 2 h in air, respectively. We investigated the dependence of tunability and dissipation factor on annealing temperature and different Ba/Sr ratios. It was found that the tunability increased dramatically and dissipation factor decreased obviously with increasing annealing temperature, and Ba_0.6Sr_0.4TiO₃ thin films annealed at 1100°C for 2 h have a tunability of 46.9% at 80 kV/cm bias filed and a dissipation factor of 0.008 at 1 MHz.     

High-temperature superconducting delay lines and filters onsapphire and thinned LaAlO3 substrates

The very low microwave surface resistance of high-temperature-superconductor (HTS) thin films allows the realization of microwave devices with performance superior to those made by conventional technology. Superconducting delay lines, for example, have very low propagation loss and dispersion. Long, low-loss, superconducting delay lines on both thinned LaAlO₃ and sapphire substrates are presented. Delay lines with 27- and 44-ns delay have been made, for the first time, on 5-cm-diameter 254- and 127-μm-thick LaAlO₃ substrates, respectively. The insertion losses at 77 K and 6 GHz are 6 and 16 dB, respectively. Delay lines with 9-ns delay have, for the first time, been produced on M-plane sapphire substrates and demonstrate, at 77 K, an insertion loss of 1.0 dB at 6 GHz. A 2.5%-bandwidth 10 GHz four pole edge-coupled bandpass filter on M-plane sapphire substrates is also reported. The filter has minimum insertion loss of less than 0.5 dB at 9.75 GHz and 71 K     

溶液燃烧法制备纳米LaAlO3:Dy3+及发光性能研究

通过溶液燃烧法以La(NO3)3·6H2O,Dy(NO3)3·9H2O和Al(NO3)3·9H2O及C2H5NO2为原材料制备纳米粉体Lal-xDyxA1O3(x=0,0.01,0.02,0.03,0.04,0.05).采用X射线衍射、扫描电子显微镜、紫外-可见漫反射光谱和荧光光谱研究晶体结构、形貌、发光强度等内容,结果表明,通过溶液燃烧法在800℃下煅烧4h,Dy3+离子进入到LaAlO3晶格中,荧光光谱分析结果表明Lal-xDyxAlO3粉体在370 nm的激发波长下,发光主峰位于423 nm处,在掺杂比例为0.03时发光强度最高,其禁带宽度5.54 eV与理论值5.6 eV相近.     

Tuning the color purity of LaAlO3:Eu3+ red phosphor by the cross relaxation

Precisely adjusting the color purity of LaAlO3:Eu3+ red phosphor with 593 and 618 nm emissions is achieved in a strategy of suppressing transitions of high energy levels of Eu3+ ions through varying the doping concentration.As the doping concentration increases,the transitions from high levels 5D3,2,1 will be weakened,while those from 5D0 are enhanced up to a critical value with the aid of the cross relaxation.As a result,an increase of the color purity from 95.2% to 97.4% is obtained.It indicates that the ...     

Photoemission (XPS and XPD) study of epitaxial LaAlO3 film grown on SrTiO3(0 0 1)

This study investigates the tensile-strained growth of LaAlO₃ on SrTiO₃(0 0 1) substrate by molecular beam epitaxy (MBE). Growth was controlled in situ by reflection high energy electron diffraction (RHEED). The characterization was carried out ex situ by photoemission and atomic force microscopy (AFM). Photoelectron spectroscopy (XPS) reveals the development of a TiO_x-rich interface. Photoelectron diffraction (XPD) confirms that a 1.2-nm-thick pseudomorphic LaAlO₃ film has been grown on SrTiO₃(0 0 1) substrate with a perpendicular lattice parameter of 0.372±0.02 nm.     

In-situ low energy BF2+ion doping for silicon molecular beam epitaxy

An experimental study of the p-type ion dopant BF2+ in silicon molecular beam epitaxy (MBE) is described. BF2+ was used to dope MBE layers during growth to levels ranging from 1 × 10¹⁶/cm³to 4 × 10¹⁸/cm³over a growth temperature range of 650°C to 1000°C. The layers were evaluated using spreading resistance, chemical etching, and secondary ion mass spectroscopy. Complete dopant activation was observed for all growth temperatures. Remnant fluorine in the epitaxial layer was less than 2 × 10¹⁶/cm³in all cases. Diffused p-n junction diodes fabricated in BF2+-doped epitaxial material showed hard reverse breakdown characteristics.     

Optical properties of epitaxialLaF3/SrF2/GaAs(111) heterostructure waveguidesfabricated by molecular beam epitaxy

Thin film slab waveguides of lanthanum fluoride clad with strontium fluoride grown epitaxially on GaAs (111) are characterized by optical and structural techniques. Crystallinity, surface roughness, refractive indexes and propagation loss measurements suggest that these structures show promise for monolithically integrated infrared (IR) pumped IR down-conversion and visible upconversion laser devices. Propagation losses as low as 3.7 dB/cm at 633 nm were measured in samples which show waveguide propagation over distances of several centimeters. Simulation of the scattering losses due to surface roughness provides an approximate delineation of surface and nonsurface contributions to the optical loss. Typical root-mean-square surface roughness of the lanthanum fluoride layer was on the order of 3 nm. The morphology appears to be dominated by grain boundaries     

碳酸锰和纳米钛酸钡的添加对钛酸钡陶瓷的影响

以钛酸丁酯和乙酸钡为起始原料,采用液相法制备了纳米钛酸钡。研究了纳米钛酸钡和碳酸锰的掺杂对普通亚微米级钛酸钡的形貌及介电性能的影响。结果表明,在普通钛酸钡中加入一定量的纳米钛酸钡可以促进晶粒的生长,同时提高陶瓷的介电常数。而在普通钛酸钡中加入一定量的碳酸锰则可以抑制晶粒的生长。但同时添加碳酸锰和纳米钛酸钡,碳酸锰对晶粒生长的抑制作用将居于主导地位,并且此时钛酸钡陶瓷的介电常数温度特性曲线与单独添加锰离子时的走势基本相同,室温附近的介电常数峰将由于钛酸钡陶瓷的细晶效应而弥散。     

Si衬底上具有Poly-Si/SiO2堆叠缓冲层的Pb (Zr0.52Ti0.48)O3 存储电容

在p型Si衬底上沉积多晶硅薄膜和Pb(Zr0.52Ti0.48)O3 (PZT)薄膜形成过渡层。测试淀积在多晶硅上的PZT薄膜不同退火温度的X射线衍射峰。Pt/PZT/poly-Si电容被研究。由于PZT薄膜的铁电极化特性,金属/铁电/多晶硅/二氧化硅/Si结构存储电容在650度退火展示了其顺时针的电压-电容曲线。存储窗口随着SiO2电容和PZT电容的耦合比的增加而增大。     

Effects of NH3 plasma passivation on N-channelpolycrystalline silicon thin-film transistors

The NH₃-plasma passivation has been performed on polycrystalline silicon (poly-Si) thin-film transistors (TFT's), It is found that the TFT's after the NH₃-plasma passivation achieve better device performance, including the off-current below 0.1 pA/μm and the on/off current ratio higher than 10⁸, and also better hot-carrier reliability than the H₂-plasma devices. Based on optical emission spectroscopy (OES) and secondary ion mass spectroscopy (SIMS) analysis, these improvements were attributed to not only the hydrogen passivation of the defect states, but also the nitrogen pile-up at SiO₂/poly-Si interface and the strong Si-N bond formation to terminate the dangling bonds at the grain boundaries of the polysilicon films. Furthermore, the gate-oxide leakage current significantly decreases and the oxide breakdown voltage slightly increases after applying NH₃-plasma treatment. This novel process is of potential use for the fabrication of TFT/LCD's and TFT/SRAM's     

N型表面钝化晶体硅太阳电池Al2O3/SiNx减反射叠层的优化研究

减反射特性是进一步提高N型太阳电池能量转换效率的重要因素之一。研究采用Al2O3/SiNx叠层优化了N型太阳电池的减反射特性,并通过理论模拟和实验测量系统地探讨了叠层中SiNx厚度对表面反射性能的影响。研究证实在Al2O3层上增加一层SiNx,可以有效地优化表面减反射性质,从而提高N型太阳电池的光伏性质。     

Low threshold current GaAs/AlGaAs GRIN-SCH lasers grown bymolecular beam epitaxy on Si3N4 masked substrates

High-performance single-quantum-well graded-refractive index separate confinement heterostructure (SQW GRINSCH) laser have been grown by molecular beam epitaxy on Si₃N₄ patterned GaAs (100) substrates. Lasers grown on stripe windows orientated in the [011] direction have optical waveguiding and current confinement supplied by facetting occurring during growth. Lasers fabricated on 10 μm wide Si ₃N₄ openings have threshold currents as low as 15 mA for a 500 μm-long cavity. The current density required to reach optical transparency is 144 A/cm²; an internal quantum efficiency of 81%, and a peak optical power of 70 mW per facet has been obtained. Device performance comparable to ridge lasers is observed in a self-aligned laser process     

Characterization of the annealing impact on La2O3/HfO2 and HfO2/La2O3 stacks for MOS applications

The impact of various rapid thermal annealing used during the integration on the La₂O₃/HfO₂ and HfO₂/La₂O₃ stacks deposited by Atomic Layer deposition was analyzed. The consequences of lanthanum localization in such stacks on the evolution of the films during the rapid thermal annealing are investigated in term of morphology, crystalline structure, silicate formation and film homogeneity as a function of the depth. It appeared that the La₂O₃ location has an impact on the temperature of the quadratic phase formation which could be linked to the formation of SiOHfLa silicate and the resistance of the films to dissolution in HF 0.05 wt%.     

Defects introduced into SrTiO3 by auto-feeding epitaxy studied using positron annihilation technique

Vacancy-type defects in SrTiO₃ were studied by means of positron annihilation. Thin CeO₂ films were grown on SrTiO₃ substrates by molecular-beam epitaxy without using an oxidant; oxygen was supplied by diffusion from the substrate. This process is referred as “auto-feeding epitaxy” (AFE). The species of defects introduced into the substrate was found to be not only oxygen vacancies but also Sr-vacancies or their complexes. CeO₂ films were grown also on MgO, yttria-stabilized zirconia and sapphire substrates using AFE, and these substrates were characterized by positron annihilation.     

Role of N2 during chemical dry etching of silicon oxide layers using NF3/N2/Ar remote plasmas

In this work, the role of N₂ gas during the chemical dry etching of silicon oxide layers in NF₃/N₂/Ar remote plasmas was investigated by analyzing the species in the plasma, the reaction by-products in the exhaust, and the chemical properties of the etched surface. Increasing the N₂ gas flow rate resulted in an initial increase in the oxide etch rate up to a maximum value, followed by a subsequent decrease. The increased etch rate of the silicon oxide layers was not ascribed to the increased surface arrival rate of fluorine, but to the enhanced oxygen removal from the silicon oxide caused by the formation of NO₂ molecules. Presumably, the NO radicals formed from the added N₂ gas react chemically with the oxygen in the oxide, leading to the breaking of the Si-O bonds and the effective removal of oxygen, which in turn enhances the formation of SiF₄ resulting in an increased etch rate.