循环氧化/退火制备GeOI薄膜材料及其性质研究

采用超高真空化学气相淀积系统在SOI(绝缘体上硅)衬底上生长了Si_0.82Ge_0.18外延层,通过循环氧化/退火工艺,制备出Ge组分从0.24到1的绝缘体上锗硅(SGOI)材料.采用高分辨透射电镜、拉曼散射光谱和光致发光谱表征了其结构及光学性质,对氧化过程中SiGe层中的Ge组分和应变的演变进行了分析.最后制备出11 nm厚的绝缘体上Ge材料(GeOI),具有完整的晶格结构和平整的界面.室温下观测到绝缘体上Ge直接带跃迁光致发光,发光峰值位于1540 nm,发光 关键词： GeOI 氧化 退火 光致发光谱     

Ge nanoclusters in PECVD-deposited glass after heat treatment and electron-beam irradiation

This paper reports the formation of Ge nanoclusters in silica glass thin films deposited by plasma-enhanced chemical vapor deposition (PECVD). We studied the samples by transmission electron microscopy (TEM) and Raman spectroscopy after annealing. TEM investigation shows that the Ge nanoclusters at two areas were formed by different mechanisms. The Ge nanoclusters formed in a single row along the interface of a silicon substrate and the silica glass film by annealing during high-temperature heat treatment. Ge nanoclusters did not initially form in the bulk of the film but could be subsequently formed by the electron-beam irradiation. The interface between the silicon substrate and the silica glass film was investigated by Raman spectroscopy. The shift of the Raman peaks around 286.8 cm^-1 and 495 cm^-1 suggests that the interface is a Si_1-xGe_x alloy film and that the composition x varies along the film growth direction. PACS 81.07.Bc; 78.66.Jg; 42.65.Wi     

高温处理工艺对低压MOCVD外延GaAs/Ge太阳电池的影响

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备,在Ge衬底(100)面向(111)偏9°外延生长出GaAs电池结构,对电池材料进行了X射线衍射分析另外,对由此材料制成的太阳电池进行了性能测试,测试结果表明,Ge衬底的高温处理工艺对GaAs/Ge太阳电池的电流电压特性有一定的影响试验表明,在600～700℃之间高温处理效果较好。     

超导Nb-Ge溅射膜的俄歇电子能谱及电子能谱化学分析

利用表面分析仪器俄歇电子能谱(AES)仪和电子能谱化学分析(ESCA)仪对超导Nb-Ge溅射膜进行表面和深度剖面分析,以探讨在溅射沉积成膜过程中A15结构Nb₃Ge能够稳定生长的机制,以及影响其转变温度T_c的因素。分析结果表明,超导Nb-Ge膜中含有O,C和Al等杂质,其中O的含量对T_c有重要影响。表面上未发现有聚集的Ge。Nb/Ge密度比由表面层的3.1向内部逐渐降至2.26。X射线光电子能谱(XPS)的分析表明:Nb,Ge,C和O的谱峰沿深度均有不同程度的化学位移和峰形变化,这明这些元素的化学态在膜内是复杂的。但其中Nb的变化最小,可能对高T_cA15Nb₃Ge相的生长起稳定作用。 关键词：     

Microstructural evolution and electrical properties of La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films grown on SrTiO<Subscript>3</Subscript> substrates by excimer-laser assisted metal-organic deposition

Thin films of La_0.7Ca_0.3MnO₃ were successfully grown epitaxially on (100) single-crystal SrTiO₃ substrates by excimer-laser assisted metal-organic deposition. Initial amorphous LCMO thin films were obtained by metal-organic deposition at 500 °C. Crystallization and epitaxial growth of the films was achieved using a KrF pulsed laser irradiation while the film/substrate samples were kept at 500 °C. High resolution transmission electron microscopy observations on cross-sections demonstrate the formation mechanism of the epitaxial films. The crystallization process starts at the LCMO/STO interface and grows by increasing the number of laser shots. A fully crystallized film was obtained after 5 min of irradiation. The film/substrate interface was found to be sharp and abrupt. The temperature dependence of the resistance R(T) shows various behaviors, starting from insulating to semiconducting and metal–insulator transition material during the formation of the manganite film. The oxygen content was also improved by increasing the irradiation time. Promising values of the temperature coefficient of resistance were obtained from these manganite films for prospect integration in silicon based microbolometric devices. PACS 81.15.-z; 81.15.Np; 73.61.-r; 71.30.+h     

Photoreflectance characterization of CdTe thin films grown by Molecular Beam Epitaxy on GaAs(100)

CdTe films have been grown on top of GaAs(100) by means of Molecular Beam Epitaxy (MBE) at 300 °C substrate temperature. Different procedures for the CdTe growth and for the preparation of the GaAs substrates resulted in diverse crystalline qualities of the CdTe films. We present the results obtained from PhotoReflectance (PR) measurements of these films employing HeNe and Ar-ion lasers as modulating excitation. For Ar excitation, the ratio of CdTe to GaAs signal strength for the E ₀ transition is enhanced, allowing a differentiation of the contributions from film and substrate. Both the PR line shape and intensity are correlated to the structural quality of the CdTe films. One of the samples presented a below-band-gap transition of the GaAs substrate around 30±5 meV from E ₀ which is attributed to donor states produced by Te atoms diffused in the interface; this result demonstrates the high sensitivity of the photoreflectance technique to the structural properties of interfaces.     

Pd-Si薄膜固相反应的透射电子显微镜研究

本工作利用透射电子显微术研究了Pd-Si薄膜固相反应的初始生成相及生成相Pd₂Si与(111)取向Si衬底的取向关系随Pd膜厚度、退火温度等因素的变化规律。实验结果表明:在衬底保持室温的条件下,Pd沉积到Si(111)上时也能够生成一层外延的Pd₂Si,其厚度足以在常规的选区电子衍射中产生明显的信号。在170℃退火时,Pd-Si反应即可持续到生成200nm厚的外延的Pd₂Si。在Pd膜厚度为400nm的条件下,Pd₂Si与Si(111)衬底的取向关系为[0001]_(Pd2Si)轴织构。 关键词：     

Island formation in Ge films on GaAs(1 1 0)

The early stages of GaAs (1 1 0)/Ge heterojunction formation at room temperature have been investigated by Auger spectroscopy. Comparison between the experimental results and the predictions of simple deposition models indicates that the growth of the Ge film proceeds by island formation. A uniform overlayer starts to develop only in films thicker than 10 Å. Evidence is also found for As diffusion through the Ge film.     

Sr/Si(100)表面TiSi2纳米岛的扫描隧道显微镜研究

为了解半导体衬底与氧化物之间存在的相互作用,以及量子尺寸效应对不同再构体的影响,制备了1—2个原子层厚的TiSi₂/Si(100)纳米岛,并使用扫描隧道显微镜(STM)表征手段详细地研究了TiSi₂ /Si(100)纳米岛的电子和几何特性. 结果发现:这些纳米岛表面显示出明显的金属性;其空态STM图像具有典型的偏压依赖性:在高偏压下STM 图像由三聚物形成的单胞构成,并在低偏压下STM 图像显示为密堆积的图案,这些不同的图案反映出不同能量位的态密度有明显差异. 关键词： 2纳米岛')" href="#">TiSi₂纳米岛 Sr/Si(100)表面 扫描隧道显微镜     

Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Germanium substrate

We have described Stranski–Krastanow growth of multilayer In(Ga)As/GaAs QDs on Ge substrate by MBE. The growth technique includes deposition of a thin germanium buffer layer followed by migration-enhanced epitaxy (MEE) grown GaAs layer at 350°C. The MEE layer was overgrown by a thin low-temperature (475°C) grown GaAs layer with a subsequent deposition of a thick GaAs layer grown at 590°C. The sample was characterized by AFM, cross-sectional TEM and temperature-dependent PL measurements. The AFM shows dense formation of QDs with no undulation in the wetting layer. The XTEM image confirms that the sample is free from structural defects. The 8 K PL emission exhibits a 1051 nm peak, which is similar to the control sample consisting of In(Ga)As/GaAs QDs grown on GaAs substrate, but the observed emission intensity is lower. The similar slopes of Arrhenius plot of the integrated PL intensity for the as-grown QD sample grown on Ge substrate as well as for a reference QD sample grown on GaAs substrate are found to be identical, indicating a similar carrier emission process for both the samples. This in turn indicates coherent formation of QDs on Ge substrate. We presume due to the accumulated strain associated with the self-assembled growth of nanostructures on Ge that nonradiative recombination centers are introduced in the GaAs barrier in between the QD layers, which in turn degrades the overall optical quality of the sample.     

Band alignments at SrZrO3/Ge(0 0 1) interface: Thermal annealing effects

High-κ dielectrics SrZrO₃ were prepared on Ge(0 0 1) substrate using pulse laser deposition, and band alignments and thermal annealing effects were studied with high resolution X-ray photoemission spectroscopy. Valence and conduction band offsets at this interface were measured to be 3.26 eV and 1.77 eV, respectively. Interfacial Ge oxide layers were found at the interface. After annealing at 600 °C, the interfacial Ge oxide layers were eliminated, and the valence band offset increased to 3.50 eV, but the amorphous SrZrO₃ became polycrystalline in the meantime.     

Effects of sapphire substrate annealing on ZnO epitaxial films grown by MOCVD

The annealing effects of sapphire substrate on the quality of epitaxial ZnO films grown by metalorganic chemical vapor deposition (MOCVD) were studied. The atomic steps formed on (0 0 0 1) sapphire (α-Al₂O₃) substrate surface by annealing at high temperature was analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the ZnO films were examined by X-ray diffraction (XRD), AFM and photoluminescence (PL) measurements. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate surface. The optimum annealing temperature of sapphire substrates is given.     

高组份Al值的AlxGa1-x As和AlxGa1-x As/GaAs/AlxGa1-xAs/GaAs多层结构的MOCVD生长

用自制常压MOCVD系统,在半绝缘GaAs衬底上生长高Al组份Al_xGa_1-xAs（其x值达0.83）,和Al_xGa_1-xAs/GaAs/Al_xGa_1-xAs/GaAs多层结构,表面镜面光亮。生长层厚度从几十到十几μm可控,测试表明外延层晶格结构完整,x值调节范围宽,非有意掺杂低,高纯GaAs外延层载流子浓度n_300K=1.7×10¹⁵cm^-3,n_77K=1.4×10¹⁵cm^-3,迁移率μ_300K=5900cmcm²/V.S,μ_77K=55500cm²/V.S。用电子探针,俄歇能谱仪测不出非有意掺杂的杂质,各层间界面清晰平直。 对GaAs,AlGaAs生长层表面缺陷,衬底偏角生长温度及其它生长条件也进行了初步探讨。     

Investigation of the SiO<Subscript>2</Subscript>(Co)/GaAs heterostructures using the surface scattering of synchrotron radiation

The giant injection magnetoresistive effect has been observed in a granulated Co/SiO₂ film on a semiconductor GaAs substrate in a narrow temperature range near T = 300 K. According to the existing theory, the nature of the effect is due to the structure and physical problems of the interface layer. The spatial distribution of cobalt nanoparticles in the bulk of the Co/SiO₂ granular film and at the granular film/semiconductor substrate (GF/SS) interface has been investigated by the reflectometry and small-angle scattering of synchrotron radiation in the grazing geometry. It has been shown that the characteristic average distance between the cobalt granules in the bulk of the film is 7.3 nm. At the same time, the average distance between the granules with a vertical size of about 7.5 nm at the GF/SS interface is 32 nm. The experimental data indicate the low concentration of cobalt at the interface and the point character of the contact of the main bulk of the Co/SiO₂ film with the GaAs substrate through a relatively diluted layer of ferromagnetic cobalt granules.     

Ti薄膜与AlN陶瓷的界面反应

用X射线衍射分析、二次离子质谱、卢瑟福背散射谱、俄歇电子能谱等表面分析技术，研究了Ti膜与AlN陶瓷衬底的界面固相反应-在高真空中用电子束蒸发的方法在抛光的200℃ AlN陶瓷衬底上淀积200nm的Ti膜，并在真空恒温炉中退火-实验表明，退火中Ti膜与AlN界面发生了扩散与反应-650℃，1h退火已观测到明显的界面反应-界面反应产物主要是钛铝化物及Ti-N化合物-铝化物是Ti-Al二元化合物和Ti-Al-N三元化合物，850℃，4h退火后则主要由Ti₂AlN组成- 关键词：     

Investigation of W-Ge-N deposited on Ge as a diffusion barrier for Cu metallization

The properties of W-Ge-Nthin films were investigated as a diffusion barrier material for Cu metallization. The W-Ge-Nfilms were grown by reactive sputtering on a single crystal Ge substrate. This was followed by in-situ deposition of Cu. Diffusion barrier test was performed by annealing the film stack under Ar atmosphere. Phase identification and film crystallization were determined by X-ray diffraction. The deposited W-Ge-Nfilms remained amorphous even after high temperature annealing. The Cu diffusion profile in the film was assessed by Auger electron spectroscopy and energy dispersive spectroscopy. The results indicate that Cu diffusion was minimal in W-Ge-Nfilms even at high annealing temperatures. Interface reactions and properties were analyzed by cross-section transmission electron microscopy. The results suggest that W-Ge-Nmay be a superior diffusion barrier as compared to WN_x for Cu metallization. PACS 66.30.Ny; 68.35.Rh; 68.37.Lp; 68.60.Dv     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Interface engineering with an MOCVD grown ZnO interface passivation layer for ZrO2-GaAs metal-oxide-semiconductor devices

This work deals with the fabrication of a GaAs metal-oxide-semiconductor device with an unpinned interface environment. An ultrathin (∼2 nm) interface passivation layer (IPL) of ZnO on GaAs was grown by metal organic chemical vapor deposition to control the interface trap densities and to prevent the Fermi level pinning before high-k deposition. X-ray photoelectron spectroscopy and high resolution transmission electron microscopy results show that an ultra thin layer of ZnO IPL can effectively suppress the oxides formation and minimize the Fermi level pinning at the interface between the GaAs and ZrO₂. By incorporating ZnO IPL, GaAs MOS devices with improved capacitance-voltage and reduced gate leakage current were achieved. The charge trapping behavior of the ZrO₂/ZnO gate stack under constant voltage stressing exhibits an improved interface quality and high dielectric reliability.     

Analysis of excimer laser annealing of amorphous SiGe on La2O3//Si structures

The reduction of complementary metal oxide semiconductor dimensions through transistor scaling is in part limited by the SiO₂ dielectric layer thickness. Among the materials evaluated as alternative gate dielectrics one of the leading candidate is La₂O₃ due to its high permittivity and thermodynamic stability. However, during device processing, thermal annealing can promote deleterious interactions between the silicon substrate and the high-k dielectric degrading the desired oxide insulating properties.The possibility to grow poly-SiGe on top of La₂O₃//Si by laser assisted techniques therefore seems to be very attractive. Low thermal budget techniques such as pulsed laser deposition and crystallization can be a good choice to reduce possible interface modifications due to their localized and limited thermal effect.In this work the laser annealing by ArF excimer laser irradiation of amorphous SiGe grown on La₂O₃//Si has been analysed theoretically by a numerical model based on the heat conduction differential equation with the aim to control possible modifications at the La₂O₃//Si interface. Simulations have been carried out using different laser energy densities (0.26-0.58 J/cm²), different La₂O₃ film thickness (5-20 nm) and a 50 nm, 30 nm thick amorphous SiGe layer. The temperature distributions have been studied in both the two films and substrate, the melting depth and interfaces temperature have been evaluated. The fluences ranges for which the interfaces start to melt have been calculated for the different configurations.Thermal profiles and interfaces melting point have shown to be sensitive to the thickness of the La₂O₃ film, the thicker the film the lower the temperature at Si interface.Good agreement between theoretical and preliminary experimental data has been found.According to our results the oxide degradation is not expected during the laser crystallization of amorphous Si_0.7Ge_0.3 for the examined ranges of film thickness and fluences.     

Epitaxial growth of Nd2Hf2O7(1 1 1) thin films on Ge(1 1 1) substrates by pulsed laser deposition

Nd₂Hf₂O₇ (NHO) thin films have been epitaxially grown by pulsed laser deposition (PLD) on Ge(1 1 1) substrates. In situ reflection high-energy electron diffraction (RHEED) evolution of the (1 1 1)-oriented NHO during the deposition has been investigated and shows that the epilayer has a twin-free character with type-B stacking. Interfacial structure of NHO/Ge has been examined by high-resolution transmission electron microscopy (HRTEM). The results indicate a highly crystalline film with a very thin interface, and the orientation relationship between NHO and Ge can be denoted as (1 1 1)_NHO//(1 1 1)_Ge and . Finally, twin-free epitaxial growth of NHO with type-B orientation displays temperature dependence and the type-B epitaxy is favored at high temperature.