The doped Si/SiO2 interface

A study is reported of the influence of dopant atoms on the SiSiO₂ interface states of thermally oxidized silicon. It was found that acceptor or donor atoms induce interface states and oxide charges. The effect is largest in the case of acceptor dopants and is independent of the doping process. The influence of the dopant atoms on oxide charge is probably related to the different segregation coefficients of acceptors and donors.     

Flat-field spectrograph in SiO2/Si

The operation of a flat-field spectrograph in silica glass on silicon (SiO₂/Si) as a demultiplexer with 4-nm channel spacing in the 1.5-μm waveguide length region is demonstrated. The concept allows fabrication tolerances to be compensated simultaneously with the adjustment of fan-out. Fiber-to-fiber insertion loss of 10.1 dB and crosstalk attenuation >15 dB have been achieved     

在SiO2中掺A1对Au／纳米（SiO2／Si／SiO2）／p—Si结构电致发光的影响

利用射频磁控溅射方法,制成纳米SiO2层厚度一定而纳米Si层厚度不同的纳米（SiO2/Si/SiO2）/p-Si结构和纳米（SiO2:A1/Si/SiO2:A1)/p-Si结构,用磁控溅射制备纳米SiO2:A1时所用的SiO2/A1复合靶中的A1的面积百分比为1%。上述两种结构中Si层厚度均为1-3nm,间隔为0.2nm。为了对比研究,还制备了Si层厚度为零的样品。这两种结构在900℃氮气下退火30min,正面蒸半透明Au膜,背面蒸A1作欧姆接触后,都在正向偏置下观察到电致发光（EL）。在一定的正向偏置下,EL强度和峰位以及电流都随Si层厚度的增加而同步振荡,位相相同。但掺A1结构的发光强度普遍比不掺A1结构强。另外,这两种结构的EL具体振荡特性有明显不同,对这两种结构的电致发光的物理机制和SiO2中掺A1的作用进行了分析和讨论。     

Visible light emitting Si/SiO2 superlattices

Six-period superlattices of Si/SiO₂ have been grown at room temperature using molecular beam epitaxy. With this mature technology, the ultra-thin (1–3 nm) Si layers were grown to atomic layer precision. These layers were separated by 1 nm thick SiO₂ layers whose thickness was also well controlled by using a rate-limited oxidation process. The chemical and physical structures of the multilayers were characterized by cross-sectional TEM, X-ray diffraction, Raman spectroscopy, Auger sputter-profile, and X-ray photoelectron spectroscopy. The analysis showed that the Si layer is free of impurities and is amorphous, and that the SiO₂/Si interface is sharp (0.5 nm). Photoluminescence (PL) measurements were made at room temperature using 457.9 nm excitation. The PL peak occurred at wavelengths across the visible range for these multilayers. The peak energy position E was found to be related to the Si layer thickness d by E (eV) = 1.60+0.72d⁻² in accordance with a quantum confinement mechanism and the bulk amorphous-Si band gap.     

An epitaxial Si/SiO2 superlattice barrier

An epitaxial strain layer Si/SiO₂ superlattice barrier (SLSB) for silicon formed by monolayers of adsorbed oxygen, sandwiched between adjacent thin silicon layers deposited with molecular beam, showed good epitaxy with an effective barrier height of 1.7 eV. Such a barrier should be important for future quantum devices in silicon, as well as new applications in conventional MOS technology.     

Interface states in SiSiO2 interfaces

Interface state parameters were studied in MOS capacitors over a wide range of energy by conductance and capacitance measurements at various temperatures from room temperature to liquid nitrogen temperature. A new technique was developed for analysis of the data which allows to obtain the density of states, the capture cross section, the surface potential and the dispersion parameter from the conductance and capacitance vs. frequency curves. The density of interface states as well as the electron capture cross section were found to be a function of energy only and to be independent of temperature. Maxima in the density of states have not been found.     

Laser-induced self-organization of nano-wires on SiO2/Si interface

Original observation of new graded band gap structures formed on the surface of elementary Si semiconductor at studying the optical properties of Si nano-hills formed at the SiO₂/Si interface by pulsed Nd:YAG laser irradiation is reported. The self-organized nano-hills on Si surface are characterized by a strong photoluminescence in the visible range of spectrum with a shoulder extended to the long-wave part of the spectrum. The feature is explained by the quantum confinement effect in nano-hills-nano-wires of gradually changing diameter.     

Electrical Characteristics of Memory Devices With a High- k HfO2 Trapping Layer and Dual SiO2/Si3N4 Tunneling Layer

A novel device structure with a high-k HfO₂ charge storage layer and dual tunneling layer (DTL) (SiO₂/Si₃N₄) is presented in this paper. Combining advantages of the high trapping efficiency of high-k materials and enhanced charge injection from the substrate through the DTL, the device achieves a fast program/erase speed and a large memory window. The device demonstrates excellent retention due to its physically thick DTL and also improved endurance without any increase of programming V_th throughout the cyclic test as compared with SONOS Flash memory devices using an Si₃N₄ trapping layer.     

Determination of Si/SiO2 interface roughness using weaklocalization

The interface roughness of intentionally textured Si/SiO₂ interfaces was measured using the quantum weak localization (WL) correction to the electrical conductivity at low temperatures. The deduced roughness was confirmed by observation of the Si surface replicas by atomic force microscopy (AFM). Quantitative agreement between the two methods was found (Δ=1.2 to 1.4 Å from WL and 1.35 Å from AFM). For a surface with artificially induced texture, it is found that WL can easily distinguish a significant increase in roughness relative to the smooth surfaces. AFM confirms this qualitative conclusion     

Complex-Coupled DFB Laser Using a Buried SiO2 Grating

In this letter, we report a distributed feedback (DFB) laser having a dielectric grating formed by SiO and InP to explore both the large refractive index difference and the partial gain coupling. Epitaxy lateral overgrowth by metal-organic chemical vapor deposition is conducted to grow the top p-type InP waveguide layer in the dielectric grating template. An index coupling coefficient of about 250 cm is estimated on the laser vertical waveguide structure. The insulating nature of the dielectric grating also partially blocks the injection current flow and modulates the optical gain of the active quantum-well region underneath it. A prototype DFB laser was fabricated and showed a stable single-mode operation with a sidemode suppression ratio larger than 47 dB measured at room temperature and continuous-wave operation. The technology developed can also be used for other applications that require high efficiency grating structures.     

Electroluminescence from Au/Si/SiO2/p-Si structure

Si/SiO₂ films have been grown using the two-target alternation magnetron sputtering technique. The thickness of the SiO₂ layer in all the films was 8 nm and that of the Si layer in five types of the films ranged from 4 to 20 nm in steps of 4 nm. Visible electroluminescence (EL) has been observed from the Au/Si/SiO₂/p-Si structures at a forward bias of 5 V or larger. A broad band with one peak 650–660 nm appears in all the EL spectra of the structures. The effects of the thickness of the Si layer in the Si/SiO₂ films and of input electrical power on the EL spectra are studied systematically.     

SOI planar photonic crystal fabrication: Etching through SiO2/Si/SiO2 layer systems using fluorocarbon plasmas

Dry plasma etching of sub-micron structures in a SiO₂/Si/SiO₂ layer system using Cr as a mask was performed in a fluorocarbon plasma. It was determined that the best anisotropy could be achieved in the most electropositive plasma. A gas composition yielding the desired SOI planar photonic crystal structures was optimized from the available process gases, Ar, He, O₂, SF₆, CF₄, c-C₄F₈, CHF₃, using DC bias data sets. Application of the c-C₄F₈/(noble gas) chemistry allowed fabrication of the desired SOI planar photonic crystal. The average etching rates for the pores and ridge waveguide regions were about 71 and 97 nm/min, respectively, while the average SiO₂/Si/SiO₂ to Cr etching selectivity for the ridge waveguide region was about 33:1 in case of the c-C₄F₈/90%Ar plasma with optimized parameters.     

Surface charge and stress in the Si/SiO2 system

A model for the stress distribution in thermally oxidised silicon slices has been developed using beam theory and bimetallic strip theory. The stresses have been confirmed by making lattice parameter measurements on oxidised silicon using the APEX X-ray diffraction technique. The often suggested relationship between the surface charge density at the Si/SiO₂ interface and the stress in the silicon surface has been investigated and shown to be inconsistent. Finally, analysis of the variation of surface charge density with oxide thickness has caused us to postulate the presence of both positively and negatively charged centres at the interface.     

Cu/Ta/SiO_2/Si多层结构的纳米压痕研究

利用磁控溅射方法在Si衬底上沉积钽层以及铜层,并利用纳米压痕技术对Cu/Ta/SiO_2/Si多层膜结构进行了硬度和弹性模量的表征,研究发现多层膜结构的硬度随着薄膜厚度的增加而降低,然而弹性模量与膜厚之间并没有这样的关系。利用聚焦离子束（FIB）工艺将纳米压痕区域剖开,并通过透射电子显微镜（TEM）表征发现在纳米压痕过后,钽以及二氧化硅界面有了明显的分层现象,这一点表明层与层之间较弱的键合在相对大的负荷下遭到了破坏。     

Capacitance voltage characterization of poly SiSiO2Si structures

The high frequency C-V characteristics of poly SiSiO₂Si capacitors have been studied. It is shown that the poly SiSiO₂Si capacitor C-V characteristics are significantly different from the corresponding metal-SiO₂Si capacitor due to field penetration into the poly Si layer. A comparison of the theoretical and measured C-V characteristics gives an estimate of the surface state charge density at the poly SiSiO₂ interface and indicates that the surface potential behavior of this interface is trap and surface state dominated up to poly silicon impurity concentrations of approximately 10¹⁷ cm^?3.     

Effect of SiO2/Si interface roughness on gate current

In many theoretical investigations of the electric-tunnel effect through an ultrathin oxide in metal-oxide-semiconductor (MOS) structure, it is commonly assumed that the oxide is of uniform thickness. One example of nonuniformity in oxides is interface roughness. Interface roughness effects on direct tunneling current in ultrathin MOS structures are investigated theoretically in this article. The roughness at SiO₂/Si interface is described in terms of Gauss distribution. It is shown that the transmission coefficient increases with root-mean-square (rms) roughness increasing, and the effect of rms roughness on the direct tunneling current decreases with the applied voltage increasing and increases with rms roughness increasing.     

Tunneling of electrons from Si into thermally grown SiO2

Accurate measurements of electron tunneling at the SiSiO₂ interface were performed using the decay of surface potential following charging of the exposed oxide surface by positive corona ions. The surface potential was measured by an automated Kelvin-probe arrangement. Comparison of results for various substrate dopings, crystallographic orientations and oxide film thicknesses is presented. A model for tunneling based on electrons being confined within the lowest subband at the SiSiO₂ interface is also discussed and compared to the Fowler-Nordheim expression.     

磁控溅射法生长CeO2/Si薄膜及其发光性质

利用反应磁控溅射法对CeO2薄膜的生长规律进行了研究.通过实验发现,溅射时氧气和氩气的比例对薄膜的成分和晶体质量有很大影响.在室温下测试了CeO2薄膜的PL谱,结果表明CeO2薄膜的发光主要来自于氧缺陷.     

Charge storage peculiarities in poly-Si–SiO2–Si memory devices with Si nanocrystals rich SiO2

The paper focuses on the study of charge trapping processes in non-volatile memory metal-oxide-silicon (MOS) structures with Si nanocrystal floating gate formed by Si ion implantation. Careful electrical studies of the MOS structures based on the analysis of the capacitance–voltage (C–V) characteristics during pulse charge injection in the oxide enabled the distinguishing of the electron emission from the nanoclusters and the charge trapping in structural defects of the dioxide matrix. The trapping model is discussed.     

Finite element analysis of LiNbO3 waveguides with Si orSi/SiO2 overlay

LiNbO₃ waveguides with Si overlays are emerging as a basic building block for a variety of integrated-optic components, including modulators, high-efficiency gratings, and narrowband WDM filters. However, the development and optimization of these devices are, in large part, hindered by the lack of understanding of the specifics of the Si-on-LiNbO₃ structure which appear to differ dramatically from those of the Si and LiNbO₃ waveguides, considered separately. In this work, we provide a specific insight into the waveguiding properties of vertically stacked Si-on-LiNbO₃ waveguides. In particular, we present a detailed theoretical analysis of the effect of the Si film on the modal characteristics (propagation constant and field distribution) of the structure. The vectorial finite element method (VFEM) is used to numerically investigate a step-index and graded-index single-mode channel waveguide in LiNbO₃, with a Si or Si/SiO₂ multimode overlay. We show that for ~70% of all Si thicknesses, in the range from 0 to 1.6 μm, the highest order normal mode of the entire structure has more than 99.9% of the total energy confined in the LiNbO₃ region, i.e., beneath the Si overlay. This fact is quite intriguing given the fact a planar Si layer of submicron thickness on bulk LiNbO₃ is already multimoded. Furthermore, we show that the effective mode index of the structure is considerably modified compared to that of the LiNbO₃ waveguide while the propagation loss is, on the other hand, practically unaffected (~0.3 dB/cm) even in the presence of the lossy Si film, as confirmed by our previous experimental results. Evidently, large modulation of the effective index and low-loss propagation provide an ideal combination of properties suitable for the fabrication of high-reflectance corrugated waveguide gratings, essential for a number of practical devices, in particular, WDM filters