Microstructures of InN film on 4H-SiC (0001) substrate grown by RF-MBE

InN film was grown on 4H-SiC (0001) substrate by RF plasma-assisted molecular beam epitaxy (RF-MBE). Prior to the growth of InN film, an InN buffer layer with a thickness of ~ 5.5 nm was grown on the substrate. Surface morphology, microstructure and structural quality of InN film were investigated. Micro-structural defects, such as stacking faults and anti-phase domain in InN film were carefully investigated using transmission electron microscopy (TEM). The results show that a high density of line contrasts, parallel to the growth direction (c-axis), was clearly observed in the grown InN film. Dark field TEM images recorded with diffraction vectors g = 1120 and g = 0002 revealed that such line contrasts evolved from a coalescence of the adjacent misoriented islands during the initial stage of the InN nucleation on the substrate surface. This InN nucleation also led to a generation of anti-phase domains.     

GaN缓冲层对生长InN薄膜的影响

采用金属有机物化学气相沉积(MOCVD)方法生长六方相InN薄膜，利用氮化镓(GaN)缓冲层技术制备了高质量薄膜，得到了其能带带隙0.7eV附近对应的光致发光光谱(PL). 通过比较未采用缓冲层，同时采用低温和高温GaN缓冲层，以及低温GaN缓冲层结合高温退火三种生长过程，发现低温GaN缓冲层结合高温退火过程能够得到更优表面形貌和晶体质量的InN薄膜，同时表征了材料的电学性质和光学性质. 通过对InN薄膜生长模式的讨论，解释了薄膜表面形貌和晶体结构的差异.     

Correlation Between Threading Dislocations and Nonradiative Recombination Centers in InN Observed by IR Cathodoluminescence

The correlation between threading dislocations (TDs) and nonradiative recombination centers in InN films was investigated by infrared cathodoluminescence (CL). Samples were grown on nitridated (0001) sapphire substrates with a low-temperature-grown InN buffer layer by radio frequency molecular-beam epitaxy (RF-MBE). Panchromatic CL images of the InN films showed a high density of dark spots in a range of 10⁸ cm⁻² to 10⁹ cm⁻². The sample with a higher density of TDs had a higher density of CL dark spots. A depth-dependent CL measurement confirmed that CL dark spots aligned almost vertically in the film like TDs. Reasonable correlation between TDs and the nonradiative regions was also observed by a cross-sectional CL image of the InN film regrown on a microfaceted InN template, in which the TD density was dramatically reduced in part. These results suggest that threading dislocations act as nonradiative recombination centers in InN.     

Structure and photoluminescence properties of InN films grown on porous silicon by MOCVD

In this work, indium nitride (InN) films were successfully grown on porous silicon (PS) using metal oxide chemical vapor deposition (MOCVD) method. Room temperature photoluminescence (PL) and field emission scanning electron microscopy (FESEM) analyses are performed to investigate the optical, structural and morphological properties of the InN/PS nanocomposites. FESEM images show that the pore size of InN/PS nanocomposites is usually less than 4 μm in diameter, and the overall thickness is approximately 40 μm. The InN nanoparticles penetrate uniformly into PS layer and adhere to them very well. Nitrogen (N) and indium (In) can be detected by energy dispersive spectrometer (EDS). An important gradual decrease of the PL intensity for PS occurs with the increase of oxidation time, and the PL intensity of PS is quenched after 24 h oxidization. However, there is a strong PL intensity of InN/PS nanocomposites at 430 nm (2.88 eV), which means that PS substrate can influence the structural and optical properties of the InN, and the grown InN on PS substrate has good optical quality.     

TiO2薄膜的宽光谱特性椭偏法研究

为了获得TiO2薄膜的光学常数,采用德国SENTECH生产的SE850宽光谱反射式光谱型椭偏仪,测量和分析了用光控自动真空镀膜机沉积在K9玻璃上的单层TiO2薄膜,得到了TiO2薄膜在300nm~2500nm宽谱上的光学常数曲线和薄膜厚度.根据TiO2的薄膜特性及成膜特点,考虑了表面粗糙层和界面层对薄膜性能的影响,建模时采用Cauchy指数模型和Tauc-Lorentz模型,对建立的各种模型测量得到的数据进行了分析和比较.结果表明,模型基底/Tauc-Lorentz模型/表面粗糙层可以得到最小的均方差为0.5544,得到的TiO2薄膜的厚度的测量值与TFCalc软件的计算值最接近.该研究结果对TiO2薄膜多层膜膜系设计和制备有参考价值.     

倾斜角沉积技术制备ZnS双折射雕塑薄膜

使用倾斜角沉积(GLAD)的电子束蒸发技术,制备了倾斜角度在60°~85°之间的ZnS双折射雕塑薄膜(STF)。使用X射线衍射(XRD)和扫描电镜(SEM)检测了ZnS薄膜的结晶状态和断面形貌,使用Lamda-900分光光度计测量了薄膜在不同的偏振光入射时的透过率。研究发现,室温下倾斜沉积ZnS薄膜断面为倾斜柱状结构,且薄膜的结晶程度不高。在相同的监控厚度时,随倾斜角度增大,沉积到基片上的薄膜厚度逐渐变小,但仍然大于余弦曲线显示的理论厚度。根据偏振光垂直入射时薄膜的透过光谱计算了不同角度沉积的薄膜的折射率和双折射。结果显示当倾斜角度为75°时,薄膜的双折射效应最显著,此时Δn=0.044。     

绝缘膜负带电时的表面局部电场与二次电子返回特性

为分析IC多层版图扫描电镜(SEM)对准检测所利用的负带电成像原理,采用Mott弹性散射截面和修正的Bethe非弹性碰撞公式,对点照射入射电子在绝缘膜中的散射过程进行了Monte Carlo模拟,得到负带电绝缘物表面的局部电位分布.在此基础上计算了二次电子从表面出射后在局部场作用下的运动轨迹,获得了SEM像的二次电子信号电流.结果表明,在弱负带电条件下,照射点处表面电位越低,返回表面的二次电子就越多,对应的二次电子信号电流越弱.此结果与SEM实验中图像亮度随照射时间的变化规律相符     

ITO:Mo透明导电薄膜的制备

利用通过固相烧结法得到的自制靶材,采用脉冲激光沉积法(PLD)在不同的衬底温度下沉积得到薄膜。通过XRD对它们的晶体结构进行分析,对薄膜断面进行扫描,测量其薄膜厚度。利用四探针法和霍尔效率测试仪,分别对薄膜的电阻率和载流子浓度及迁移率进行测量和分析。最后,用分光光度计对薄膜的透光率进行测量和分析,并计算了薄膜的禁带宽度。结果表明,在500℃下沉积的薄膜综合性能最好,电阻率可达2.611×10-4Ω.cm,透光率在90%以上,禁带宽度为4.29eV。     

VLSI用低介电常数含氟碳膜研究

用等离子体增强化学气相沉积(PECVD)法制备了不同工艺条件下的含氟碳膜。测量了薄膜的厚度和介电常数,并用傅立叶红外光谱分析了薄膜化学结构,发现薄膜成分和介电性与沉积工艺密切相关,对薄膜的SEM分析表明所得薄膜均匀致密。控制适当的工艺条件,可沉积理想的超大规模集成电路(VLSI)用钝化膜。     

阴极荧光联合分析系统在III族氮化物研究中的应用

利用高性能阴极荧光（CL）联合分析系统对几类典型的III族氮化物材料进行测试分析.在光谱研究中,利用CL紫外可见光谱系统,对c面蓝宝石衬底上生长的AlxGa1-xN薄膜进行阴极荧光单色谱测试分析,揭示了CL的激发强度与发光带之间的变化关系.进一步研究了掺Mg的Al0.5Ga0.5N薄膜的带边和杂质能级发光机理.利用CL近红外光谱系统对InN薄膜的阴极发光特性进行了研究,验证了InN实际光学带边Eg在0.77eV附近.利用微区分析（CLmapping）系统,可在紫外波段确切地给出材料不同波长的荧光发光区这一特点,对HVPE生长的自支撑GaN衬底进行了SEM和CL微区的对比分析,研究了GaN的位错类型和分布.     

Molecular Beam Epitaxy of Graded-Composition InGaN Nanowires

We report the growth of graded InGaN nanowires by plasma-assisted molecular beam epitaxy. Wire composition is linearly graded from InN to GaN along the length of each wire. The large lattice mismatch between GaN and InN (11%) introduces tensile strain in the graded region, which results in cracking of the wires. Growing with reverse grading (i.e., GaN to InN) results in crack-free nanowires. The composition is measured by energy-dispersive x-ray spectroscopy of individual nanowires performed in a scanning transmission electron microscope, and strain is measured by high-resolution x-ray diffraction.     

Sputtered growth of high mobility InN thin films on different substrates using Cu-ZnO buffer layer

This work reports the growth of c-plane textured InN thin films on Cu-ZnO buffered silicon, c-sapphire, bulk GaN and quartz substrates. A Cu-ZnO buffer layer was deposited on all the substrates before the growth of InN film. A highly c textured film was obtained on sapphire and quartz substrates. Structural properties were calculated using XRD and Raman analysis. It was observed that, induction of Cu-ZnO buffer layer reduced the lattice mismatch between Si/GaN substrates and InN film. The bandgap of the films was obtained using UV visible reflectance spectroscopy. Hall measurements show high mobility films in the range of 119–223 cm²/Vs and an electron concentration of 10¹⁹. These results are in good agreement with previous results but are first time recorded using RF magnetron sputtering. Surface topography of the films showed smooth surfaces, which are due to reduced lattice mismatch between film and the substrate.     

Ion Beam Analysis of Amorphous and Nanocrystalline Group III-V Nitride and ZnO Thin Films

The ion beam analysis (IBA) techniques of Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), nuclear reaction analysis (NRA), and particle-induced x-ray emission (PIXE) have been used to quantitatively determine composition, uniformity, impurity, and elemental depth profiles of major, minor, and trace elements of group III-V nitride and zinc oxide (ZnO) thin films prepared by various growth techniques. The IBA revealed that an amorphous GaN film prepared by ion beam assisted deposition (IBAD) has large variations in film thickness and composition coupled with typically 10–20% oxygen that was found to be essential to stabilize their amorphous structure. The IBA characterization of plasma-assisted molecular beam epitaxy (PAMBE) grown GaN, InN, and InCrN films revealed composition, impurity, and uniformity information of the films. The IBA of ZnO films prepared by radio frequency (RF) sputtering showed that the Zn/O ratio often varied significantly over the film thickness. Hydrogen was found to be a major impurity in the films with around one present in the as-deposited ZnO films. It is clearly shown that the nondestructive, quantitative, and rapid IBA measurements are very useful to develop and optimize growth protocols in respect to film thickness, stoichiometry, and especially in regard to hydrogen and oxygen impurities for group III-V nitride and ZnO thin films prepared by various growth techniques.     

Features of InN growth by nitrogen-plasma-assisted MBE at different ratios of fluxes of group-III and -V elements

The results of investigations of the effect of the ratios of fluxes of the Group-III and -V elements on the structural and optical properties of an InN film deposited by plasma-assisted molecular-beam epitaxy (MBE) are presented. It is shown that the InN layer consists of free-standing nanocolumns at a flux ratio of III/V < 0.6. InN growth becomes two-dimensional (2D) in the ratio range 0.6 < III/V < 0.9; however, the InN layer has a nanoporous structure. Upon passage to metal-rich conditions of growth (III/V ～1.1), the InN layer becomes continuous. The passage from 3D to 2D growth is accompanied by an increase in the threading-dislocation density. It results in a decrease in the photoluminescence (PL) intensity of InN at room temperature. The electron concentration in the InN layers amounts to ～5 × 10¹⁸ cm^–3, which results in a shift of the PL-signal peak to the wavelength region of 1.73–1.8 μm and to a shift of the absorption edge to the region of ～1.65 μm.     

Optical Hall Effect in Hexagonal InN

Measurements of the optical Hall effect in naturally doped high-quality wurtzite-structure InN thin films by generalized ellipsometry reveal that both the surface and the interior (bulk) free electron densities decrease with power-law dependencies on the film thickness. We discover a significant deviation between the bulk electron and dislocation densities. This difference is attributed here to the existence of surface defects with activation mechanism different from bulk dislocations and identifies the possible origin of the so far persistent natural n-type conductivity in InN. We further quantify the anisotropy of the -point effective mass.     

氮化时间对RF-MBE法生长InN薄膜晶体结构的影响

采用射频等离子体分子束外延(RF-MBE)技术在蓝宝石(Al2O3)衬底上外延生长了InN薄膜,在生长之前对其进行不同时间的氮化处理.通过扫描电子显微镜(SEM)和X射线衍射(XRD)对薄膜的形貌和结构进行了表征,发现氮化时间小于60 min时获得的InN薄膜的晶体结构为多晶且表面粗糙,而氮化时间为60 min及120 min时获得的InN薄膜为单晶结构,表面粗糙度有所下降.分析表明,氮化时间对InN薄膜的晶体结构有很重要的影响.     

Sharp Infrared Emission from Single‐Crystalline Indium Nitride Nanobelts Prepared Using Guided‐Stream Thermal Chemical Vapor Deposition

Single‐crystalline InN nanobelts have been synthesized using Au as the catalyst by a guided‐stream thermal chemical vapor deposition technique. The resultant InN nanobelts typically have widths ranging from 20 to 200 nm, a width to thickness ratio of 2–10, and lengths of up to several tens of micrometers. Structural analysis shows that these InN nanobelts have a wurtzite structure and exhibit a rectangular cross section with self‐selective facets, i.e., the nanobelts are enclosed only by ± (001) and ± (11?0) planes with [110] being the exclusive growth direction along their long axis. This facet selectivity can be understood by the differences in the surface energies of the different facets. Photoluminescence (PL) spectra of InN nanobelts show a sharp infrared emission peak at 0.76 eV with a full width at half maximum of 14 meV, narrower than the values reported for InN epilayers. The integrated PL intensity is found to increase linearly with the excitation power, which suggests that the observed PL can be attributed to direct band‐to‐band emission.     

HWE生长条件对CdTe/Si薄膜结构特性的影响

研究了热壁外延(HWE)生长条件对Si(100)衬底上沉积外延的多晶CdTe薄膜的晶粒尺寸和取向的影响.用SEM和XRD技术分析了不同外延时间、不同衬底温度及不同源温下外延膜的表面形貌和结构特征.SEM发现随着外延时间的增加或衬底温度的提高,晶粒尺寸明显增大;XRD显示所有的外延薄膜均为面心立方结构,并高度显示优势取向(111),且随着衬底温度或薄膜厚度的增加,(111)峰的衍射强度增加,显示薄膜的择优取向更好.其原因是面心立方结构中,(111)表面具有的表面自由能最低.通过对不同外延时间下薄膜厚度的测试发现,薄膜具有加速生长趋势.衬底温度及源温对外延层厚度均有较大的影响.     

膜厚对泡沫镍负载TiO2纳米薄膜附着度和光电响应的影响

采用溶胶-凝胶法与高温水热法相结合的复合方法制备了以泡沫镍为基底的不同膜层厚度的TiO2纳米薄膜光电极,并用场发射扫描电子显微镜（SEM）与电化学工作站对样品进行了表面形貌表征与光电性能测试。结果表明,膜层厚度为10层的TiO2纳米薄膜光电极的材料附着度最高,且具有最强的光电响应。研究结果为进一步优化泡沫镍负载TiO2纳米薄膜光电极的制备提供了有益参考。     

Strain status in ZnO film on sapphire substrate with a GaN buffer layer grown by metal-source vapor phase epitaxy

ZnO film of 8 μm thickness was grown on a sapphire (0 0 1) substrate with a GaN buffer layer by a novel growth technique called metal-source vapor phase epitaxy (MVPE). The surface of ZnO film measured by scanning electron microscope (SEM) is smooth and shows many regular hexagonal features. The full width at half maximum (FWHM) of ZnO(0 0 2) and (1 0 2) ω-scan rocking curves are 119 and 202 arcsec, corresponding a high crystal quality. The status of the strain in ZnO thick film was particularly analyzed by X-ray diffraction (XRD) ω-2θ scanning. The results show that the strain in ZnO film is compressive, which is also supported by Raman scattering spectroscopy. The compressive strain can solve the cracking problem in the quick growth of ZnO thick film.