First-principles study of the segregation of boron dopants near the interface between crystalline Si and amorphous SiO2

We investigate the stability of boron dopants near the interface between crystalline Si and amorphous SiO₂ through first-principles density functional calculations. An interstitial B is found to be more stable in amorphous SiO₂ than in Si, so that B dopants tend to segregate to the interface. When defects exist in amorphous SiO₂, the stability of B is greatly enhanced, especially around Si floating bond defects, while it is not significantly affected near Si–Si dimers, which are formed by O-vacancy defects.     

Suppression of boron segregation by interface Ge atoms at SiGe/SiO2 interface

We investigate the migration pathway and barrier for B diffusion at SiGe/SiO₂ interface through first-principles density functional calculations. Similar to the diffusion mechanism reported for Si/SiO₂ interface, a substitutional B, which initially forms a B-self-interstitial complex in SiGe, diffuses to the interface and then to the oxide in form of an interstitial B. At the defect-free interface, where bridging O atoms are inserted to remove interface dangling bonds, it is energetically more favorable for the interstitial B to intervene in the Ge–O bridge bond rather than the Si–O bridge bond at the interface. As a result of the B intervention, interface Ge atoms significantly enhance the stability of B-related defects in the interface region and thereby act as traps for B dopants. At the interface with the Ge–O bridge bond, the overall migration barrier for B diffusion from SiGe to SiO₂ is estimated to be about 3.7 eV, much higher than the reported value of about 2.1 eV at Si/SiO₂ interface. Our results provide a clue to understanding the experimental observation that B segregation toward the oxide is suppressed in SiGe/SiO₂ interface.     

On the kinetics of the generation of point defects in the Si-SiO2 system

The results of studies of the point-defect generation kinetics in the Si-SiO₂ system by means of Electron Spin Resonance (ESR) and InfraRed (IR) absorption spectroscopy are presented. The influence of oxidation conditions (oxidation temperature and time, cooling rate) on the defect structure of the Si-SiO₂ interface has been studied. It is shown that this influence can be explained by the model of point-defect generation proposed by Tan and Gösele, and the structural properties of the Si-SiO₂ system can be improved by an appropriate choice of the oxidation conditions.     

Effect of the Nickel Impurity on the Rate of Surface Generation of Charge Carriers at the Si–SiO2 Interface

The effect of the nickel impurity on the generation characteristics of the Si–SiO₂ interface is investigated by the method of isothermal capacitance relaxation. It is demonstrated that doping by the nickel impurity increases the rate of surface generation of charge carriers and the spread of this parameter from structure to structure. The effects observed are associated with the existence of defect-impurity complexes formed in doped structures as a result of interaction of impurity clusters (precipitates) with native defects in the transition layer at the Si–SiO₂ interface.     

Annealing Induced Degradation of Thermal SiO2 On (100)Si: Point Defect Generation

The structural degradation of thermal SiO₂ on (100)Si under isochronal post oxidation vacuum annealing (POVA) has been probed by electron spin resonance (ESR). The degradation process, studied in the range T_an = 950–1250 °C, is established as intense point defect generation including E′_γ, E′_δ, EX and the elusive predominant degradation center S. Thermally activated generation is revealed over broad T_an ranges for the two most populous defects, S and E′_γ, with a common activation energy ～1.6eV. Depth profiling after heating at 1200°C shows that the S centers predominantly reside near the oxide borders, generally in anticorrelation with the E′_γ distribution. The S center susceptibility has been inferred from conventional ESR signal intensity monitoring as well as from revealed anisotropic demagnetisation effects. It is found Curie-Weiss type with critical temperature of ～ 1.3 K. Newly observed weak hyperfine structure may comply with the S center being an E′-like defect.     

Coupling between Ge-nanocrystals and defects in SiO2

Room temperature photoluminescence (PL) at around 600 nm from magnetron-sputtered SiO₂ films co-doped with Ge is reported. The PL signal is observed in pure SiO₂, however, its intensity increases significantly in the presence of Ge-nanocrystals (Ge-nc). The PL intensity has been optimized by varying the temperature of heat treatment, type of gas during heat treatment, concentration of Ge in the SiO₂ films, and gas pressure during deposition. Maximum intensity occurs when Ge-nc of around 3.5 nm are present in large concentration in SiO₂ layers deposited at fairly high gas pressure. Based on time resolved PL, and PL measurements after α-particle irradiation or H passivation, we attribute the origin of the PL to a defect in SiO₂ (probably an O deficiency) that is excited through an energy transfer from Ge-nc. There is no direct PL from the Ge-nc; however, there is a strong coupling between excitons created in the Ge-nc and the SiO₂ defect.     

Ionoluminescence studies of combustion synthesized Dy doped nano crystalline forsterite

Ionoluminescence (IL) of nano crystalline Mg₂SiO₄:Dy³⁺ pellet samples bombarded with 100 MeV Si⁺⁸ ions with fluences in the range (1.124–22.480) × 10¹² ions cm⁻² have been studied. Two prominent IL bands with peaks at ∼480 nm and ∼580 nm and a weak band with peak at ∼670 nm are recorded. The characteristic peaks are attributed to luminescence center activated by Dy³⁺ ions due to the transitions ⁴F_9/2→⁶H_15/2,⁶H_13/2 and ⁶H_11/2. It is found that IL intensity initially decreases rapidly and then continuous to decrease slowly with further increase in ion fluence. The reduction in the Ionoluminescence intensity with increase of ion fluence might be attributed to degradation of Si–O ( 2ν₃) bonds present on the surface of the sample and/or due to lattice disorder produced by dense electronic excitation under heavy ion irradiation.     

Influence of Si/SiO2 interface properties on electrical performance and breakdown characteristics of ultrathin stacked oxide/nitride dielectric films

In this work, the influence of Si/SiO₂ interface properties, interface nitridation and remote-plasma-assisted oxidation (RPAO) thickness (<1 nm), on electrical performance and TDDB characteristics of sub-2 nm stacked oxide/nitride gate dielectrics has been investigated using a constant voltage stress (CVS). It is demonstrated that interfacial plasma nitridation improves the breakdown and electrical characteristics. In the case of PMOSFETs stressed in accumulation, interface nitridation suppresses the hole traps at the Si/SiO₂ interface evidenced by less negative V_t shifts. Interface nitridation also retards hole tunneling between the gate and drain, resulting in reduced off-state drain leakage. In addition, the RPAO thickness of stacked gate dielectrics shows a profound effect in device performance and TDDB reliability. Also, it is demonstrated that TDDB characteristics are improved for both PMOS and NMOS devices with the 0.6 nm-RPAO layer using Weibull analysis. The maximum operating voltage is projected to be improved by 0.3 V difference for a 10-year lifetime. However, physical breakdown mechanism and effective defect radius during stress appear to be independent of RPAO thickness from the observation of the Weibull slopes. A correlation between trap generation and dielectric thickness changes based on the C-V distortion and oxide thinning model is presented to clarify the trapping behavior in the RPAO and bulk nitride layer during CVS stress.     

Hydrogen-related defect creation at the Si(100)–SiO2interface of metal-oxide-semiconductor field effect transistors during hot electron stress

We explore the hydrogen-related microstructures involved in hot electron defect creation at the Si(100)–SiO₂interface of metal-oxide-semiconductor field effect transistors. Based on the energetics of hydrogen desorption from the interface between silicon and silicon-dioxide, we argue that the hard threshold for hydrogen-related degradation may be considerably lower than the previously assumed value of 3.6 eV. Also, hydrogen atoms released from Si–H bonds at the interface by hot electron stress are trapped in bulk silicon near the interface.     

多孔TiO2/Al/SiO2纳米复合结构的紫外光吸收特性研究

在SiO₂玻璃衬底上用脉冲激光沉积(PLD)技术,分别沉积Ti和Ti/Al膜,经电化学阳极氧化成功制备了多孔TiO₂/SiO₂和TiO₂/Al/SiO₂纳米复合结构. 其中TiO₂薄膜上的微孔阵列高度有序,分布均匀. 实验研究了Al过渡层对多孔TiO₂薄膜光吸收特性的影响. 结果表明：无Al过渡层的多孔TiO₂薄膜其紫外吸收峰在27 关键词： 2薄膜')" href="#">多孔TiO₂薄膜 阳极氧化 紫外光吸收     

多孔TiO2/Al/SiO2纳米复合结构的紫外光吸收特性研究

在SiO₂玻璃衬底上用脉冲激光沉积(PLD)技术，分别沉积Ti和Ti/Al膜，经电化学阳极氧化成功制备了多孔TiO₂/SiO₂和TiO₂/Al/SiO₂纳米复合结构. 其中TiO₂薄膜上的微孔阵列高度有序，分布均匀. 实验研究了Al过渡层对多孔TiO₂薄膜光吸收特性的影响. 结果表明：无Al过渡层的多孔TiO₂薄膜其紫外吸收峰在27     

Luminescent silicon nanocrystal dots fabricated by SiCl4/H2 RF plasma-enhanced chemical vapor deposition

Luminescent nanocrystalline Si dots were fabricated directly on thermally grown SiO₂ at 120°C by conventional RF plasma-enhanced chemical vapor deposition using tetrachlorosilane, SiCl₄ and H₂. As-deposited Si dot exhibits photoluminescence (PL) in the visible region, consisting of two broad bands corresponding to photon energies of 1.38 and 1.48 eV. Storage in air enhances PL and shifts the PL peak energy to higher wavelengths for dots of diameter less than 10 nm. Fourier transform attenuated total reflection absorption spectroscopy (FTIR-ATR) study reveals that the spontaneous oxidation proceeds until saturation after 70 h at dot sizes of 3–5 nm. The relationship between PL intensity, blueshift of PL peak energy, and surface termination species during oxidation indicates that these changes are attributed to the increased density of radiative centers at the Si nanocrystal dot/SiO₂ interface and enhancement of the quantum confinement effect.     

Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method

Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions.     

The hybrid photocatalyst of TiO2–SiO2 thin film prepared from rice husk silica

The TiO₂–SiO₂ thin film was prepared by self-assembly method by mixing SiO₂ precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO₂ and even anatase TiO₂ but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti–O–Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO₂ was incorporated into the film. The self-assembly TiO₂–SiO₂ thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO₂ are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO₂:TiO₂) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.     

Electronic band structure of pseudo-binary AlB2-like hexagonal silicides SrNixSi2−x as novel low-TC superconductors

The very recently discovered pseudo-binary hexagonal silicide SrNi_xSi_2−x, which exhibits low-T_C superconductivity, was examined theoretically to understand the effect of the unusual doping type (partial replacement of Si by Ni) on the electronic band structure of this material. Besides, the possible factors of the stabilization of the hexagonal AlB₂-type structure of SrSi₂ upon substitution of Ni for Si, and the solubility limit of Ni in SrNi_xSi_2−x are discussed in terms of competing Si–Si, Si–Ni, and Ni–Ni bonds.     

Absorption cross-sections and lifetimes as a function of size in Si nanocrystals embedded in SiO2

The photoluminescence (PL) emission yield of Si nanocrystals embedded in SiO₂ depends on their size and on Si–SiO₂ interface passivation. In this work we aim at clarifying the relative importance of both contributions by studying lifetimes and absorption cross-sections as a function of size, for samples with and without passivation in forming gas. We find that while the PL lifetime increases steadily (quasi-linear dependence), the radiative lifetime increases exponentially with the nanocrystal size. Thus, as expected, radiative oscillator strengths are much smaller for large nanocrystals, but this reduction is partially compensated by a less effective quenching at interfacial non-radiative states. The absorption cross-section per nanocrystal rises as the nanocrystal size decreases, for all excitation wavelengths, implying that the variation of oscillator strength dominates over the reduction of the density of states. Passivation processes do not affect the emission mechanism and increase the emission yield while reducing the density of non-radiative recombination centers at the Si–SiO₂ interface (P_b centers).     

Spectroscopic properties of Er in a oxyfluoride glass and upconversion and temperature sensor behaviour of Er/Yb-codoped oxyfluoride glass

Spectroscopic properties of Er³⁺-singly doped SiO_2––BaF₂–ZnF₂ glass have been investigated on the basis of the Judd–Ofelt theory. Upconversion emissions in Er³⁺/Yb³⁺-codoped SiO₂–BaF₂–ZnF₂ glass have been observed under 980 nm excitation. The temperature dependence of fluorescence intensity ratio corresponding to the two thermally coupled levels (²H_11/2, ⁴S_3/2) has been studied and it is concluded based on the results that the method can be possibly applied for temperature sensing.     

Enhancement of the emission yield of silicon nanocrystals in silica due to surface passivation

The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO₂ has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO₂ interface (P_b centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of P_b centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the P_b defects, increasing at the same time the PL yield and the lifetime.     

同步辐射光激励的二氧化硅薄膜刻蚀研究

利用热氧化法在硅晶片上生长SiO₂薄膜，结合光刻和磁控溅射技术在SiO₂薄膜表面制备接触型钴掩模，通过掩模方法在硅表面开展了同步辐射光激励的表面刻蚀研究，在室温下制备了SiO₂薄膜的刻蚀图样.实验结果表明：在同步辐射光照射下，通入SF₆气体可以有效地对SiO₂薄膜进行各向异性刻蚀，并在一定的气压范围内，刻蚀率随SF₆气体浓度的增加而增加，随样品温度的下降而升高；如果在同步辐射光照射下，用SF₆和O₂的混合气体作为反应气体，刻蚀过程将停止在SiO₂/Si界面，即不对硅刻蚀，实现了同步辐射对硅和二氧化硅两种材料的选择性刻蚀；另外，钴表现出强的抗刻蚀能力，是一种理想的同步辐射光掩模材料. 关键词： 同步辐射刻蚀 接触型钴掩模 二氧化硅薄膜     

The influence of SiCp oxidized on the interface layer and thermal conductivity of SiCp/Al composites

In this work, oxidation of silicon carbide particles (SiCp) at elevated temperature and its influence on the interface layer and thermal conductivity of SiCp/ZL101 composites prepared using pressure infiltration process were investigated respectively. It is found that initial temperature for the oxidation of SiCp is about 850?°C, and that the oxidation increment of SiCp and the thickness of SiO₂ layer increase with the increase in pre-oxidation temperature and time, when the oxidized temperature exceeds 1100?°C, or the duration time exceeds 2?h at 1100?°C, a small amount of ablation will take place on the SiCp, as well as the oxidized layer has some loss. The formation of SiO₂ layer can provide certain interface reactions with interface layers (3.1–6.36?μm), and the higher the thickness of SiO₂ layer, the thicker the interface layer in SiCp/Al composites. However, the thickness of SiO₂ layer is more than 5.9?μm, which is not benefit for the formation of interface layer. With the increase in the thickness of interface layer, thermal conductivity declines, but is not linear.