Synthesis and characterization of heteroepitaxial GaN films on Si(111)

We report crack-free and single-crystalline wurtzite GaN heteroepitaxy layers have been grown on Si (111) substrate by metal-organic chemical vapor deposition(MOCVD). Synthesized GaN epilayer was characterized by X-ray diffraction(XRD), atomic force microscope (AFM) and Raman spectrum. The test results show that the GaN crystal reveals a wurtzite structure with the <0001> crystal orientation and XRD ω-scans showed a full width at half maximum (FWHM) of around 583 arcsec for GaN grown on Si substrate with an HT-AlN buffer layer. In addition, the Raman peaks of E₂^high and A₁(LO) phonon mode in GaN films have an obvious redshit comparing to bulk GaN eigen-frequency, which most likely due to tensile strain in GaN layers. But the AO phonon mode of Si has a blueshit which shows that the Si substrate suffered a compressive strain. And we report that the AlN buffer layer plays a role for releasing the residual stress in GaN films.     

平面光波导膜的ECR-PECVD制备及特性研究

采用微波电子回旋共振等离子体增强化学气相沉积技术 ,在单晶硅衬底上制备了用于平面光波导的SiO2 薄膜 ,研究了沉积速率与工艺参数之间的关系 ,并对射频偏置对成膜特性的影响作了初步实验研究。通过X射线光电子能谱、傅立叶变换红外光谱、扫描电镜、原子力显微镜、以及扫描隧道显微镜三维形貌和椭偏仪等测量手段 ,分析了样品的薄膜结构和光学特性等。结果表明 ,在较低温度下沉积出均匀致密、性能优良的SiO2 薄膜。此外 ,还成功制备出掺Ge的SiO2 薄膜 ,并可以精确控制掺杂浓度 ,以适应不同光波导芯的要求     

Characteristics of In_(0.52)Al_(0.48)As Grown on InP(100) Substrates by Molecular Beam Epitaxy: Growth Optimisation and Effects of Si Doping

Growth of In0.52Al0.48As epilayers on InP (100) substrates by molecular beam epitaxy at a wide range of substrate tempreatures (470~550℃) and at different Si doping levels has been carried out. Low temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) analyses shaw a strong dependence of the PL and XRD linewidths, XRD intensity ratio (Lepi/Isub), and lattice-mismatch on the substrate temperature. The X-ray diffraction peaks of samples grown at law temperatures show a composition of smaller peaks, indicating the presence of disorder due to alloy clustering. Raman scattering measurements of the same samples show an additional higher energy mode at 273 cm-1 in addition to the InAs-like and AlAs-like longitudinal-optic (LO) phonon modes. Samples doped with Si show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. Supported be observations of a reduction in both the AlAs-like and InAs-like LO phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased, the PL intensity also shows in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.     

Spectroscopic analysis on metal-oxide-semiconductor light-emitting diodes with buried Si nanocrystals and nano-pyramids in SiO(x) film

The difference between the white and near-infrared electroluminescence of metal-oxide-semiconductor light-emitting diodes fabricated on 1,100 degrees C-annealed Si-rich SiO(x)/p-Si substrate with interfacial pyramidal Si dots (Si nano-pyramids) was characterized. By changing the substrate temperature and induced coupled plasma power during the plasma enhanced chemical vapor deposition of Si-rich SiO(x) films, the effects of the growth conditions on the defect- and Si nano-pyramid-related carrier transport and Si nanocrystal-related electroluminescence spectroscopy were also investigated. The annealed Si-rich SiO(x)/p-Si films grown at higher synthesized substrate temperate (350 degrees C) show the larger Si nano-pyramids precipitating near the Si/SiO2 interface. The indium tin oxide/Si-rich SiO(x)/p-Si/Al metal-oxide-semiconductor light-emitting diodes with Si-rich SiO(x) films exhibit different white-light electroluminescence spectra at wavelengths from 400 to 650 nm. The Si nanocrystal-related electroluminescence spectra at 650-850 nm are confirmed, whereas the electroluminescence spectra are shorter wavelengths is attributed to oxygen related defects. These defects become an electron-preferred transporting path within the Si-rich SiO(x) film, whose densities are decreased by increasing the substrate temperature or reducing the induced coupled plasma power. Defect-related white-light electroluminescence emits power for a relatively short lifetime. The lifetime can be lengthened and the electroluminescence power can be raised simultaneously by increasing deposition temperature to 350 degrees C and adjusting the induced coupled plasma power to a threshold of 30 W, which effectively increases the densities of Si nanocrystals and nano-pyramids in the Si-rich SiO(x) film with Si concentration of up to 40 at%. A nearly defect-free Si-rich SiO(x) sample can be grown under such conditions, which contributes to the most stable and largest near-infrared electroluminescence with the longest lifetime, although the power-current slope of purely Si nanopyramid related electroluminescence at near-infrared wavelengths is slightly lower.     

Infrared and raman spectroscopic studies of optically transparent zirconia (ZrO2) films deposited by plasma-assisted reactive pulsed laser deposition

Plasma-assisted pulsed laser deposited zirconia (ZrO(2)) films were studied by Fourier transform infrared (FT-IR) and Raman spectroscopy for structural characterization and thermal stability in combination with optical characterization by spectroscopic ellipsometry and optical transmission measurements. Only the monoclinic ZrO(2) phase was positively identified from the infrared and Raman spectra of the as-deposited ZrO(2) films, which show excellent optical transparency from the ultraviolet to the near infrared as revealed by optical characterization. The as-deposited ZrO(2) films are free of any SiO(x) interfacial layer when deposited on silicon. The prepared ZrO(2) films exhibit good thermal stability in their structural, optical, and interfacial properties up to 900 °C. Upon annealing above 1100 °C, a silicon oxide interfacial layer forms due to the oxidation of the silicon substrate surface by the oxygen diffused from the oxide film to the silicon substrate at high temperatures.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

Liquid-phase epitaxy of 2H-SiC film on a (0001) 4H-SiC substrate in Li-Si melt

We first applied a liquid-phase epitaxy (LPE) method to the growth of 2H-SiC to obtain an oriented 2H-SiC layer. The LPE growth was performed on a (0001) 4H-SiC substrate in a Li-Si-C melt at 850 °C. A LPE layer grew on the carbon face of the (0001) 4H-SiC substrate with the area of about 1 × 1 mm². The thickness and morphology of the LPE layer were confirmed by scanning electron microscope (SEM), and the polytype of the LPE layer was determined using a high-resolution transmission electron microscope (HR-TEM) and a Raman spectroscopy. SEM measurements revealed that the thickness of the LPE layer was 50 μm and that this layer developed with a hexagonal shape. HR-TEM observations and Raman spectral analysis showed that 2H-SiC layer grows on 4H-SiC substrate with the relationship of (0001) 2H-SiC (0001) 4H-SiC. In this study, we first succeeded to grow <0001>-axis-oriented 2H-SiC films and concluded that the LPE technique is applicable to the growth of oriented 2H-SiC films in the Li-Si melt.     

Transparent thin-film characterization by using differential optical sectioning interference microscopy

We propose an optical thin-film characterization technique, differential optical sectioning interference microscopy (DOSIM), for simultaneously measuring the refractive indices and thicknesses of transparent thin films with submicrometer lateral resolution. DOSIM obtains the depth and optical phase information of a thin film by using a dual-scan concept in differential optical sectioning microscopy combined with the Fabry-Perot interferometric effect and allows the solution of refractive index and thickness without the 2pi phase-wrapping ambiguity. Because DOSIM uses a microscope objective as the probe, its lateral resolution achieves the diffraction limit. As a demonstration, we measure the refractive indices and thicknesses of SiO2 thin films grown on Si substrate and indium-tin-oxide thin films grown on a glass substrate. We also compare the measurement results of DOSIM with those of a conventional ellipsometer and an atomic force microscope.     

Few-layer graphene direct deposition on Ni and Cu foil by cold-wall chemical vapor deposition

We report an alternative synthesis process, cold-wall thermal chemical vapor deposition (CVD), is replied to directly deposit single-layer and few-layer graphene films on Ar plasma treated Ni and Cu foils using CH4 as carbon source. Through optimizing the process parameters, large scale single-layer graphene grown on Ni foil is comparable to that grown on Cu foil. The graphene films were able to be transferred to other substrates such as SiO2/Si, flexible transparent PET and verified by optical microscopy, Raman microscopy and scanning electron microscopy. The sheet resistance and transmission of the transferred graphene films on PET substrate were also discussed.     

反应蒸发沉积的纳米硅氧化硅薄膜的发光及其氧的存在形态

通过改变蒸发源、衬底温度和氧的流量 ,用反应蒸发法制备了不同晶粒尺寸的Si/SiOx 薄膜。用X射线衍射、X光电子能谱和红外光谱分别测试了薄膜的结构、组分及氧在薄膜中的存在形态。实验发现氧的存在形态与蒸发条件密切相关 :对以硅为蒸发源的样品 ,衬底温度较低时 ,以间隙氧形态存在。随着衬底温度的升高 ,SiOx 量逐渐增多 ,间隙氧逐渐减少 ,72 0℃以上产生SiO2 。氧流量的增加有利于间隙氧的生成和氧含量的增加 ;对以SiO为蒸发源的样品 ,衬底温度较低时 ,主要以间隙氧的形态存在 ,同时存在SiO2 和SiOx。随着衬底温度的升高 ,有利于SiOx 和SiO2 的增加。 80 0℃退火后 ,SiOx 增多 ,同时产生大量SiO2 白硅石。荧光光谱表明 :薄膜的发光跟氧的存在形态密切相关 ,其可能原因是纳米硅被大量宽禁带的SiO2 或SiOx基体包裹所产生的量子效应。     

Studies of surface and interface phonon polariton characteristics of wurtzite ZnO thin film on wurtzite 6H-SiC substrate by p-polarized infrared attenuated total reflection spectroscopy

The surface and interface phonon polariton characteristics of a wurtzite ZnO thin film grown on a wurtzite 6H-SiC substrate are investigated by p-polarized infrared attenuated total reflection spectroscopy. Two absorption dips corresponding to the leaky surface phonon polariton (SPP) mode of ZnO and the interface phonon polariton (IPP) mode of ZnO/6H-SiC are clearly observed at 558 and 916 cm^− 1, respectively. The observations are in good agreement with the results determined from the theoretical surface polariton dispersion curve simulated by means of an anisotropy model. Finally, the effects of the ZnO thin film thickness on the SPP and IPP modes are deduced from the theoretical calculations.     

Nanocontact heteroepitaxy of thin GaSb and AlGaSb films on Si substrates using ultrahigh-density nanodot seeds

A film of GaSb grown epitaxially on a Si substrate is a direct transition semiconductor useful for application as a light source in Si photonics and channel material in next-generation field effect transistors because its energy bandgap is close to the optical fibre communication wavelength and it possesses high carrier mobility. Here, we report a novel method for heteroepitaxial growth of high-quality GaSb/Si films, despite having a lattice mismatch as large as ～ 12%, using elastically strain-relaxed GaSb nanodots with ultrahigh density as seed crystals for film growth. The nanodot seed crystals were grown epitaxially by restricted contact with the Si substrate through nanowindows in an ultrathin SiO(2) film on the Si substrate. A light-emitting diode containing GaSb/Si films with a thickness of ～ 90 nm fabricated by this method operated at room temperature. The growth method was also used to fabricate AlGaSb films of high quality. Our method provides a new avenue for heteroepitaxial growth of high-quality film in systems with large lattice mismatch.     

Studying 3C-SiC epilayers grown on the (0001)C face of 6H-SiC substrates

Epitaxial 3C-SiC films grown on the (0001)C face of 6H-SiC substrates by sublimation epitaxy in vacuum have been studied. The results of x-ray diffraction measurements show evidence of a rather high structural perfection of silicon carbide epilayers. The Raman spectroscopy data confirm that the 3C-SiC layer grows immediately on the 6H-SiC substrate without any transition layers. It is concluded that the structures under consideration are well suited for the investigation of a two-dimensional electron gas at the 3C-SiC/6C-SiC heterojunction     

反应蒸发制备nmSi-SiOx发光薄膜

报道了用真空反应蒸发制备nmSi/SiOx 薄膜 ,制备出含有不同纳米尺寸硅颗粒的薄膜 ,研究了不同条件下得到的nmSi SiOx 薄膜的结构和组分。实验发现以SiO为蒸发源制备的薄膜能够实现光致发光。初步分析nmSi SiOx 薄膜发光机制可能是由纳米硅量子效应引起的 ,界面效应和缺陷对薄膜PL可能没有贡献 ,解释了有纳米硅颗粒存在但观察不到PL的原因     

Au/(Si/SiO2)/p型Si结构的可见电致发光研究

Ｓｉ／ＳｉＯ２薄膜采用射频磁控溅射技术制备,当正向偏压大于５Ｖ时即可观测到来自不同Ｓｉ层厚度的Ａｕ／（Ｓｉ／ＳｉＯ２）／ｐ－Ｓｉ结构在室温下的可见电致发光,其发光谱峰位均位于６６０ｎｍ处,测得的各种储藏坟下的发光峰位不随正向偏压的升高而移动。突验结果表明光发射主要来自于ＳｉＯ２层中的发光中心上的复合发光。     

Optical functions of transparent thin films of SrTiO(3), BaTiO(3), and SiO(x) determined by spectroscopic ellipsometry

A procedure is presented for accurately determining the thickness, optical functions, and surfaceroughness characteristics of thin-film insulators from two-channel spectroscopic polarization-modulation ellipsometry data. For films with minimal surface roughness, the optical functions can be determined over the entire measured spectrum; for rougher films, the analysis of the spectroscopic ellipsometry data yields meaningful values of the optical functions only in the transparent region. In general, the films must be transparent in a given range of wavelengths sampled by the ellipsometer so that at least two interference oscillations can be observed. The use of the procedure is illustrated with the determination of the optical functions of SrTiO(3) and BaTiO(3) thin films grown on MgO, and of SiO(x) films grown on Si. For SrTiO(3) and BaTiO(3), the thin-film results are compared with the measured optical functions of the respective bulk materials.     

InAs/GaAs nanostructures grown on patterned Si(001) by molecular beam epitaxy

The potential benefit from the combination of the optoelectronic and electronic functionality of III-V semiconductors with silicon technology is one of the most desired outcomes to date. Here we have systematically investigated the optical properties of InAs quantum structure embedded in GaAs grown on patterned sub-micron and nanosize holes on Si(001). III-V material tends to accumulate in the patterned sub-micron holes and a material depletion region is observed around holes when GaAs/InAs/GaAs is deposited directly on patterned Si(001). By use of a 60?nm SiO(2) layer and patterning sub-micron and nanosize holes through the oxide layer to the substrate, we demonstrate that high optical quality InAs nanostructures, both quantum dots and quantum wells, formed by a two-monolayer InAs layer embedded in GaAs can be epitaxially grown on Si(001). We also report the power-dependent and temperature-dependent photoluminescence spectra of these structures. The results show that hole diameter (sub-micron versus nanosize) has a strong effect on the structural and optical properties of GaAs/InAs/GaAs nanostructures.     

The electrical and interface properties of metal-ferroelectric (lanthanum substituted bismuth titanate: BLT)-insulator-semiconductor (MFIS) structures with various insulators

We have investigated metal-ferroelectric-insulator semiconductor (MFIS) structures with lanthanum substituted bismuth titanate (BLT) as a ferroelectric layer and lanthanum oxide (LO) or zirconium silicate (ZSO) as an insulating buffer layer between BLT and Si substrate. The morphology of BLT films deposited on LO or ZSO oxide was not changed due to the good thermal stability of LO and ZSO films. But an interface reaction between BLT and buffer layer started at high annealing temperature (750 °C), which was confirmed by transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The maximum memory window was 3.59 V at a sweep voltage of 7 V with the LO film annealed at 650 °C and a thickness of 5 nm. With BLT/LO annealed at 750 °C, the window was decreased due to the reaction between the BLT film and LO. The memory window was about 1 V lower with a ZSO film because ZSO film has a lower dielectric constant than LO film. The MFIS structure annealed at 750 °C had a lower leakage current density because the electrical properties of the buffer layer (La oxide or Zr silicate) were improved by the thermal process.     

Guided-mode-resonance-coupled plasmonic-active SiO(2) nanotubes for surface enhanced Raman spectroscopy

We demonstrate a surface enhanced Raman scattering (SERS) substrate by integrating plasmonic-active SiO(2) nanotubes into Si(3)N(4) gratings. First, the dielectric grating that is working under guided mode resonance (GMR) provides enhanced electric field for localized surface plasmon polaritons on the surface of metallic nanoparticles. Second, we use SiO(2) nanotubes with densely assembled silver nanoparticles to provide a large amount of "hot spots" without significantly damping the GMR mode of the grating. Experimental measurement on Rhodamine-6G shows a constant enhancement factor of 8?～?10 in addition to the existing SERS effect across the entire surface of the SiO(2) nanotubes.     

常压化学气相沉积方法制备非晶硅薄膜及其光致发光性能研究

使用改进的常压化学气相沉积(APCVD)系统制备了非晶硅薄膜,测量了样品的光致发光特性,使用Raman光谱和X射线光电子能谱(XPS)谱测量了薄膜的微结构特征.样品在523 nm出现发光峰,Raman光谱和XPS谱表明制备的薄膜结构中存在富氧相和富硅相的分相现象,分析认为相界面的存在是产生发光的原因.Raman光谱分峰结果表明薄膜中存在纳米晶粒.