GaN基半导体上BiFeO_3薄膜的生长与性能研究

采用脉冲激光沉积法在(0001)取向的GaN以及AlGaN/GaN调制掺杂结构上制备了(111)取向的BiFeO3(BFO)薄膜。首先在导电氧化物SrRuO3和TiO2缓冲层包覆的GaN上制备了BFO薄膜,分析了在GaN上生长的BFO薄膜的面外取向、外延关系、表面形貌以及电学性能等性质。然后,在AlGaN/GaN调制掺杂结构上采用TiO2缓冲层生长了BFO薄膜,并采用光刻工艺分别在AlGaN表面制备Ti/Al/Ti/Au欧姆电极和BFO表面制备Ni/Au肖特基电极以形成二极管结构。C-V测试表明,由于BFO铁电薄膜极化的作用,BFO/TiO2/AlGaN/GaN结构具有1 V左右的逆时针窗口。     

激光剥离Al2O3/GaN中GaN材料温度场的模拟

对激光剥离Al2O3/GaN技术,建立了紫外脉冲激光辐照过程中GaN外延层内热传导理论模型。计算分析了不同能量密度脉冲激光辐照时,GaN外延层内的温度场分布,由此得到激光剥离的阈值条件。采用紫外KrF准分子激光器对Al2O3/GaN样品进行激光剥离实验,样品表面显微镜和端面扫描电镜(SEM)测试照片说明,计算结果与实验现象相符。进一步分析表明,脉冲激光的能量密度和频率是实现激光剥离的关键参数,适当选取这些参数能将GaN材料内的高温区控制在100nm以内,实现高效低损伤激光剥离。     

衬底和O2/Ar气体比例对ZnO薄膜结构及性能的影响

采用直流磁控溅射法沉积了ZnO薄膜,以X射线衍射(XRD)、扫描电镜(SEM)、原子力显微镜等手段对薄膜的晶体结构和微观相貌进行了分析,并对薄膜的电学性能进行了考察.结果表明:所制备薄膜沿c轴高度择优,并具有较高的电阻率;ZnO薄膜的沉积速率和c轴择优度是由O2/Ar气体比例和衬底共同决定的;Au衬底上的ZnO薄膜以三维生长为主,在Al和Si衬底上出现了不同程度的薄膜二维生长;电阻率随O2/Ar气体比例的提高逐渐增加,Si衬底上薄膜的电阻率高于Al和Au衬底上的.     

SiC缓冲层用于改善硅基氮化镓薄膜的质量研究

用脉冲激光沉积法在硅衬底上沉积GaN薄膜,为了减小Si衬底与GaN薄膜之间的热失配和晶格失配引入SiC缓冲层.脉冲激光沉积后的GaN薄膜是非晶结构,将样品在氨气氛围中在950℃下退火15min.得到结晶的GaN薄膜.并用X 射线衍射、原子力显微镜、傅立叶红外吸收谱、光致发光谱研究了SiC缓冲层对GaN薄膜的结晶、形貌和光学性质的影响.     

金属缓冲层上生长GaN薄膜的结构、发光性能及其生长机理

为了解决硅衬底与GaN之间的晶格失配和热失配问题,实验尝试采用常压化学气相沉积法(APCVD),分别以金属镓(Ga)和氨气(NH3)为镓源和氮源,在加入A1、Au/Al两种金属缓冲层和不加缓冲层的硅衬底上生长氮化镓(GaN)薄膜.采用高分辨X射线衍射仪(HRXRD)、X-ray能谱仪(EDS)、场发射扫描电子显微镜(F...     

Ti-Al共掺杂Si薄膜的光电性能增强机理研究

Ti超掺杂Si(Si:Ti)薄膜是通过脉冲激光的非平衡作用，在Si中掺入超固溶度3个数量级以上的高浓度Ti杂质形成。它摆脱了Si禁带宽度的限制，具有优异的亚带隙近红外(λ=1 100～2 500 nm)光吸收性能。通过真空电子束蒸发结合紫外纳秒激光熔融的方式，制备了Ti-Al共掺杂Si(Si:(Ti-Al))薄膜，以进一步提高薄膜的亚带隙近红外光吸收性能，更好地满足近红外器件的需求。研究结果表明，Si:(Ti-Al)薄膜的薄层电阻，由本征单晶Si衬底的10⁴Ω/square量级降低至10²Ω/square量级，与Si:Ti薄膜一致。但是，Si:(Ti-Al)薄膜在亚带隙近红外波段的吸光度，较本征单晶Si衬底平均提高了7倍，最大提高了一个数量级(λ=1 800 nm处);较Si:Ti薄膜平均提高了33%,最大提高了57.2%(λ=1 200 nm处)。表面形貌分析表明，Si:(Ti-Al)薄膜的二次激光加工降低了表面光反射。薄膜成分分析表明，Si:(Ti-Al)薄膜中存在TiSi₂和AlTi。TiSi₂     

Al预沉积层对金属有机物化学气相沉积方法在Si衬底上生长AlN缓冲层和GaN外延层的影响

采用金属有机物化学气相沉积法(MOCVD)在硅(Si)衬底制备铝/氮化铝/氮化镓(Al/AlN/GaN)多层薄膜,使用光学显微镜(OM)、原子力显微镜(AFM)、X射线衍射(XRD)等手段表征AlN和GaN薄膜的微观结构和晶体质量,研究了TMAl流量对AlN薄膜和GaN薄膜的形核和生长机制的影响。结果表明,预沉积Al层能促进AlN的形核和生长,进而提高GaN外延层的薄膜质量。TMAl流量太低则预沉积Al层不充分,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与在气氛中团聚长大并沉积的低结晶度AlN薄膜之间的竞争,AlN薄膜的质量随着TMAl流量的升高而提高,GaN薄膜的质量也随之提高。TMAl流量太高则预沉积Al层过厚,AlN缓冲层的质量取决于由形核长大的高结晶度AlN薄膜与Al-Si回融蚀刻之间的竞争,AlN薄膜的质量随着TMAl流量的升高而降低,GaN薄膜的质量也随之降低。     

Ti/Al/Ni/Au与n型GaN的欧姆接触研究

通过电流 电压 (I V)特性和传输线方法 (TLM )测量研究在n型GaN上淀积Ti/Al/Ni/Au电极形成欧姆接触的机制。Ni/Au作为Ti/Al的覆盖层起了阻止Ti ,Al,Au的互扩散及抗接触层氧化的作用。在 4 0 0℃到 90 0℃范围内 ,Ti/Al/Ni/Au与n型GaN的接触电阻随温度升高先略有上升 ,到 5 0 0℃以后单调下降。而表面形貌却在合金温度高于6 0 0℃以后随温度升高逐步变差。通过两步合金法得到了n GaN上Ti/Al/Ni/Au形成的接触电阻低达 9.6 5× 1 0 - 7Ωcm2 。最后还对两步合金法形成n GaN欧姆接触的机制进行了讨论。     

光纤定位激光钎焊键合过程中钎料与镀层的界面反应

光电子封装中,光导纤维的定位键合是一项关键技术,并且焊点界面处的显微组织对于焊点的可靠性有重要影响.本文选用80Au20Sn和52In48Sn钎料实现了激光钎焊条件下的光纤键合,采用扫描电子显微镜及能谱分析的方法对于两种钎料分别与硅片上的Au/Ti镀层和光纤上的Au/Ni镀层反应形成的界面微观组织形态及形成规律进行了分析.结果表明:对于80Au20Sn钎料,除了共晶组织ζ相+δ相,在AuSn/Au/Ti镀层界面形成了大量枝状的先共晶ζ相,在AuSn/Au/Ni镀层界面形成了针状的(Au,Ni)3Sn2;对于52In48Sn钎料,在InSn/Au/Ti镀层界面形成了连续层状的Au(In,Sn)2,随着输入能量的增加,其逐渐转变为不连续的块状化合物AuIn2,在熔融钎料流的作用下部分AuIn2脱离界面进入钎料中,在InSn/Au/Ni镀层界面形成了一层极薄的Au(In,Sn)2.     

用于制备具有超光滑表面异质集成4英寸硅基砷化镓薄膜的高效离子剥离技术（英文）

在Si衬底上将单晶GaAs薄膜与其进行异质集成有望为硅基光电集成提供新的材料平台.本文基于对GaAs材料剥离机理的分析阐述,优化了GaAs薄膜转移工艺的离子注入条件.结果表明,相比于He离子单独注入,由于较小的热预算和注入后相对更低的缺陷密度, He/H离子共注入对于GaAs薄膜转移更高效.以Al₂O₃为键合介质层,通过优化的离子剥离技术成功地将4英寸GaAs薄膜转移到Si(100)衬底上.探索了包括化学机械抛光、臭氧辐照氧化和KOH清洗的表面处理工艺,以将转移后GaAs薄膜的表面质量提高到可以高质量外延的水平.在400°C退火1 h后,转移的GaAs薄膜单晶质量进一步提高, X射线摇摆曲线的半峰全宽仅为89.03 arcsec.     

In-situ and ex-situ investigations of pulsed laser ablation of Y target

High purity yttrium was ablated by using frequency quadrupled ultra-violet pulses of a Nd:YAG laser (λ = 266 nm, τ_FWHM = 7 ns) with power density of about 1 GW/cm². Laser ablation process was studied using in-situ mass spectrometry of the ablated species in combination with ex-situ analyses of both target surface and deposited films. An increase on the Y ablation rate was found at the beginning, followed by a significant drop with increasing of the number of laser pulses per site until it reaches a constant value after 40 pulses per site. Initial topographic changes on the target surface, observed by scanning electron microscope investigations, and plasma shielding effect could be the origin of these changes on the ablation rate. Careful time-integrated and -resolved mass spectrometric studies of the laser ablated material indicate evident hydridation and oxidation processes in gas phase of ablated yttrium. These results clearly suggest that high purity metallic thin films can be deposited only after a deep and prolonged laser cleaning treatment of the target surface. The present parametric studies are aimed and tailored to prepare photocathodes based on Y thin films to be used in RF photoinjectors.     

布儒斯特角显微镜及其在气液界面膜研究中的应用

布儒斯特角显微镜出现于1991年,是一种新型的能在原位测定气/液界面单分子膜形态与缺陷的仪器,本文介绍了法国、德国和本实验室安装的布儒斯特角显微镜的结构。利用布儒斯特角显微镜可以研究气-液界面上单分子膜的均匀性与缺陷,多组份混合膜中的相分离,膜中畴的取向、尺寸与形貌,来自亚相的吸附过程、松弛与压缩过程的动力学、光化学和光物理过程等。     

Hydrothermal synthesis and characterization of Bi2O3 nanowires

An alternative two-step method has been proposed for the synthesis of Bi₂O₃ nanowires with a diameter of about 40 nm from common and cost-effective Bi(NO₃)₃·5H₂O, Na₂SO₄, and NaOH. That is, first, Bi₂O(OH)SO₄ nanowires were prepared through the precipitation reaction of Bi(NO₃)₃·5H₂O and Na₂SO₄ in distilled water under the ambient condition and second, monoclinic phase Bi₂O₃ nanowires were prepared via the hydrothermal reaction of Bi₂O(OH)SO₄ and NaOH at 120 °C for 12 h. The resultant products were characterized by X-ray diffraction, field emission scanning electron microscope, and high resolution transmission electron microscopy. In addition, the photocatalytic studies indicated that the as-synthesized Bi₂O₃ nanowires were a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.     

Effects of the stacking levels on permeability characteristics and soft magnetic properties in FeCoHfAlO/AlOx multilayered films

In the communication industry, miniaturization is highly required for inductor devices. In order to miniature the dimension of inductors, high inductance is necessary. For this purpose, to employ high-permeability magnetic films enhances the inductance of inductors. For high-permeability, in-plane uniaxial anisotropy is a critical demand. The FeCoHfAlO/AlO_x multilayered films were fabricated by dc reactive magnetron sputtering. Due to the insertion of AlO_x layers, the out-of-plane uniaxial anisotropy of the FeCoHfAlO magnetic films is reduced and their resistivity is also raised. Therefore, the permeability of the FeCoHfAlO/AlO_x multilayers will be increased further. With the optimum configuration of a seven-layer structure [FeCoHfAlO (171 nm)/AlO_x (10 nm)]₇, high resistivity (ρ ~ 7490 μΩcm) and high-permeability (μ′ > 90 at 30-50 MHz) were obtained. The permeability increased nearly ten times from 9 (3 layers) to 98 (7 layers).     

NH4Cl-assisted low temperature synthesis of anatase TiO2 nanostructures from Ti powder

A simple, low temperature and low cost method, which was based on heating the mixture of Ti and NH₄Cl powders in air at 300 °C, has been developed for the controlled synthesis of anatase TiO₂ nanostructures including irregular nanoparticle aggregates, curved nanowires built up by the oriented attachment of nanoparticles, and nanoplates constructed with nanoparticles. The characterization results from X-ray diffraction and Raman spectra indicated that the as-obtained products were anatase TiO₂. Field emission scanning electron microscope images revealed that the products obtained for 3, 10 and 16 h comprised, in turn, irregular nanoparticle aggregates (8-55 nm), curved nanowires built up by the oriented attachment of nanoparticles (~ 9 nm), and nanoplates constructed with nanoparticles (~ 8 nm).     

Direct STM mapping of the superconducting energy gap in single crystal BI2SR2CACU2O8+x

Scanning tunneling spectroscopy applied to BiO cleavage planes of 90 KT _c BSCCO 2212 at 4.2 K simultaneously provides topography and localdI/dV spectra (superconducting DOS). The spectra, which are similar to recent photoemission spectra, confirm a large gap parameter (x, y) associated with an apparently gapless DOS on the uppermost layer. Transverse spatial variations of on a 100 Å scale are attributed to variations in BiO metallicity, presumably originating in oxygen stoichiometry variations in an unannealed crystal. We identify two characteristicdI/dV spectral shapes with regions of metallic and nonmetallic BiO layers, and can relate these by the McMillan model of the superconducting proximity effect. A sharply peaked spectral shape, similar to that observed in photoemission, is predicted for the metallic BiO layer induced superconducting by its proximity to the underlying CuO₂ planes. The short mean free path and short coherence length imply that both tunneling and photoemission spectra are heavily weighted toward contributions from the BiO layer in fully metallic 2212. The present results and analysis thus suggest that the superconducting proximity effect influences the lineshapes seen by both techniques.     

Synthesis and selective gas-sensing properties of hierarchically porous intestine-like SnO2 hollow nanostructures

Hierarchically porous intestine-like SnO₂ hollow nanostructures of different dimension were successfully synthesized via a facile, organic template free, H₂O₂-assisted method at room temperature. The morphology as well as texture (congregated solid sphere, intestine-like solid nanostructure, hollow core–shell one, and intestine-like hollow one) of SnO₂ materials can be controlled by varying H₂O₂ concentration and the size of intestine-like hollow SnO₂ can be tuned in the range of 20–120 nm by changing SnSO₄ concentration. The hierarchically porous intestine-like SnO₂ has high specific surface area (142 m² g⁻¹). The gas-sensing behaviors of the intestine-like SnO₂ material to different gas probes such as ethanol, H₂, CO, methane, and butane have been investigated; among them a high selectivity to ethanol was achieved.     

Scanning tunneling microscopy of laser-deposited YBa2Cu3O7 thin films on Y-stabilized zirconia substrate

The surface morphology and growth mechanism ofc-oriented YBa₂Cu₃O₇ thin films deposited on Y-stabilized zirconia substrate by laser deposition has been investigated with scanning tunneling microscopy. Both screw dislocation and layered island growth processes took place. Surface features such as screw dislocation, steps, subgrain boundaries, holes, and troughs were present, suggesting that they may act as pinning sites for flux lines. A thin layer of nonsuperconducting material with a thickness of a few angstroms is seen on the surface of the film.     

长链羧基硅RCAS的合成及氨基硅/长链羧基硅超分子膜形貌

通过氨基硅烷、十二烷基硅烷与D4的共聚反应制备了中间体氨基/十二烷基改性聚二甲基硅氧烷(RASO),再用RASO与马来酸酐反应获得了长链羧基硅(RCAS),采用红外光谱(IR)、核磁共振(1H-NMR)对其结构进行表征,在乙酸乙酯溶剂中通过超分子组装获得了单晶硅表面的ASO/RCAS超分子膜,结合原子力显微镜(AFM)对膜的形貌进行了研究。结果表明,ASO/RCAS超分子膜形貌,完全不同于氨基硅N-β-氨乙基-γ-氨丙基聚二甲基硅氧烷(ASO)和RCAS形成的硅膜的形貌,其表面针状或柱状的直立亮峰大大减少,长链烷基的倾斜弱化了表面规则有序的窗棂形貌。     

水热法一步合成纳米/微米级ZnO球

采用水热法在较低的温度(160℃)下一步合成了高纯的六方相ZnO纳米/微米球,它们是由纳米颗粒聚合而成的.讨论其生长机制发现,在这个合成体系中,H2O起到了非常关键的作用.X射线衍射(XRD)谱中各衍射峰清晰且尖锐,说明ZnO结晶性能良好.扫描电子显微镜(SEM)、场发射扫描电子显微镜(FESEM)和透射电子显微镜(TEM)照片表明,在其他条件固定的情况下,可以通过调节三乙醇胺和水的体积比有效地控制ZnO球的尺寸和形状.紫外可见吸收光谱的吸收峰随着ZnO球直径的增加出现红移现象.