The impact of ultra thin silicon nitride buffer layer on GaN growth on Si (1 1 1) by RF-MBE

Ultra thin films of pure silicon nitride were grown on a Si (1 1 1) surface by exposing the surface to radio-frequency (RF) nitrogen plasma with a high content of nitrogen atoms. The effect of annealing of silicon nitride surface was investigated with core-level photoelectron spectroscopy. The Si 2p photoelectron spectra reveals a characteristic series of components for the Si species, not only in stoichiometric Si₃N₄ (Si⁴⁺) but also in the intermediate nitridation states with one (Si¹⁺) or three (Si³⁺) nitrogen nearest neighbors. The Si 2p core-level shifts for the Si¹⁺, Si³⁺, and Si⁴⁺ components are determined to be 0.64, 2.20, and 3.05 eV, respectively. In annealed sample it has been observed that the Si⁴⁺ component in the Si 2p spectra is significantly improved, which clearly indicates the crystalline nature of silicon nitride. The high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM) and photoluminescence (PL) studies showed a significant improvement of the crystalline qualities and enhancement of the optical properties of GaN grown on the stoichiometric Si₃N₄ by molecular beam epitaxy (MBE).     

Electrical characteristics of metal-dielectric-semiconductor structures with silicon nitride prepared by reactive cathode atomization

The effect of the technology of preparation of silicon nitride in a low temperature gas discharge plasma upon the volt-ampere and volt-farad characteristics of metal-dielectricsemiconductor (MDS) structures (Al-Si₃N₄-Si-Al) is studied. It is shown that by using a heterogeneous Si₃N₄ formation reaction with ionic purification of the silicon surface, it is possible to obtain MDS structures with lower and more stable surface charge in comparison to similar structures in which the Si₃N₄ is grown by other methods (for example, gas transport reaction methods). The conductivity of the Si₃N₄ film is described approximately by the well known Frankel model, and its value is close to that of Si₃N₄ films prepared by other methods.     

Ion tracks in amorphous silicon nitride

The morphology of the tracks of swift ions revealed in amorphous silicon nitride after treatment in an HF solution is studied. The Si₃N₄/Si structures were irradiated with Fe, Kr, and W ions in the electron energy loss regime. Discontinuous tracks were recorded upon exposure to W only, with an electron energy loss of 20.4 keV nm⁻¹ being maximal for the conditions of our experiment. The results from calculations of the track formation in Si₃N₄ based on the thermal spike model are presented.     

Electronic structure of silicon nitride according to ab initio quantum-chemical calculations and experimental data

Charge transfer ΔQ = 0.35e at the Si-N bond in silicon nitride is determined experimentally using photoelectron spectroscopy, and the ionic formula of silicon nitride Si₃^+1.4N₄^−1.05 is derived. The electronic structure of α-Si₃N₄ is studied ab initio using the density functional method. The results of calculations (partial density of states) are compared with experimental data on X-ray emission spectroscopy of amorphous Si₃N₄. The electronic structure of the valence band of amorphous Si₃N₄ is studied using synchrotron radiation at different excitation energies. The electron and hole effective masses m _e ^* ≈ m _h ^* ≈ 0.5m _e are estimated theoretically. The calculated values correspond to experimental results on injection of electrons and holes into silicon nitride.     

发光多孔硅的表面氮钝化

报道对多孔硅在NH₃气中进行快速热处理的结果。红外吸收谱表明,经处理样品的表面由Si(NH)₂和Si₃N₄所覆盖,电子自旋共振谱指出,经处理的样品有相当低的悬挂键密度,光荧光谱表明,经适当条件处理的样品的发光强度与未作处理样品相比仅略有降低,而且在大气中存放三个月基本不变,这些结果表明,氮化物可以在多孔硅表面形成优良的钝化膜,这对多孔硅的实际应用及理论研究都有一定意义。     

Long silicon nitride nanowires synthesized in a simple route

Long silicon nitride (Si₃N₄) nanowires with high purity were synthesized by heating mixtures of SiO₂ powders and short carbon fibers at 1430°C for 2 h in a flowing N₂ atmosphere. The nanowires had the length of 1–2 millimeters and the diameters of 70–300 nm, and were mainly composed of ⍺-Si₃N₄, growing along the [001] direction. The vapor–solid (VS) mechanism was employed to interpret the nanowires growth.     

AFM and SNOM characterization of carboxylic acid terminated silicon and silicon nitride surfaces

Silicon and silicon nitride surfaces have been successfully terminated with carboxylic acid monolayers and investigated by atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM). On clean Si surface, AFM showed topographical variations of 0.3-0.4 nm while for the clean Si₃N₄ surface the corrugation was around 3-4 nm. After material deposition, the corrugation increased in both samples with a value in topography of 1-2 nm for Si and 5-6 nm for Si₃N₄. The space distribution of specific chemical species was obtained by taking SNOM reflectivity at several infrared wavelengths corresponding to stretch absorption bands of the material. The SNOM images showed a constant contribution in the local reflectance, suggesting that the two surfaces were uniformly covered.     

Atomic-scale studies of native point defect and nonstoichiometry in silicon oxynitride

The native point defects and mechanism of accommodating deviations from stoichiometry of Si₂N₂O crystal have been investigated using atomistic simulation techniques. This work firstly provides a reliable classical interatomic potential model derived from density functional theory calculations. The force-field parameters well reproduce the crystal structure, elastic stiffness, and dielectric constants of Si₂N₂O. It is expected that the force-field parameters are useful in future investigations on Si₂N₂O by molecular dynamic simulation. The calculated formation energies for native defects suggest that intrinsic disorder in stoichiometric Si₂N₂O is dominated by antisites and a degree of oxygen Frenkel defect may also exist in this system. In nonstoichiometric Si₂N₂O, the calculated reaction energies indicate that excess SiO₂ or Si₃N₄ is most likely accommodated by the formation of antisite in the lattice. And we also find that SiO₂ excess is energetically more favorable than Si₃N₄ surplus in Si₂N₂O.     

Fabrication of high-aspect-ratio silicon nanostructures using near-field scanning optical lithography and silicon anisotropic wet-etching process

A new process in which near-field scanning optical lithography (NSOL) is combined with anisotropic wet-etching of (110) silicon is developed for the fabrication of high-aspect-ratio (HAR) nanochannels. In the proposed process, NSOL is applied to produce nanopatterns on a commercial positive photoresist as in an optical lithography. The use of a commercial photoresist is an advantage of this process because it allows the direct application of many photoresists currently available without pretreatment, saving cost and time. A bare (110) silicon wafer coated with a thin Si₃N₄ layer, of approximately 10 nm thickness, is used as the sample and the photoresist is spincoated on the Si₃N₄ layer to a thickness of about 50–80 nm. Nanopatterning of the photoresist using a contact mode NSOL, transfer of the photoresist pattern onto the Si₃N₄ layer by reactive ion etching, and anisotropic wet etching of the silicon wafer using the patterned Si₃N₄ layer as an etch mask, lead to the intended HAR nanostructures. Fabrication of silicon nanochannels with a channel width below 150 nm and an aspect ratio greater than 3 is demonstrated. PACS 81.16.Nd; 81.16.Rf; 85.40.Hp     

Solid-state NMR investigations of Si-29 and N-15 enriched silicon nitride

We compare ²⁹Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectra from the two modifications of silicon nitride, α-Si₃N₄ and β-Si₃N₄, with that of a fully (²⁹Si, ¹⁵N)-enriched sample ²⁹Si₃¹⁵N₄, as well as ¹⁵N NMR spectra of Si₃¹⁵N₄ (having ²⁹Si at natural abundance) and ²⁹Si₃¹⁵N₄. We show that the ¹⁵N NMR peak-widths from the latter are dominated by J(²⁹Si–¹⁵N) through-bond interactions, leading to significantly broader NMR signals compared to those of Si₃¹⁵N₄. By fitting calculated ²⁹Si NMR spectra to experimental ones, we obtained an estimated coupling constant J(²⁹Si–¹⁵N) of 20 Hz. We provide ²⁹Si spin-lattice (T₁) relaxation data for the ²⁹Si₃¹⁵N₄ sample and chemical shift anisotropy results for the ²⁹Si site of β-Si₃N₄. Various factors potentially contributing to the ²⁹Si and ¹⁵N NMR peak-widths of the various silicon nitride specimens are discussed. We also provide powder X-ray diffraction (XRD) and mass spectrometry data of the samples.     

Nanosize silicon nitride: characteristic of doped powders and of the related sintered materials

The paper reports on both the characteristics of ultrafine silicon nitride powder produced by plasma synthesis and the microstructure and properties of the relative sintered material. The powder, already containing yttria and alumina as sintering aids, has a bimodal particle size distribution and it is partly amorphous. The chemical composition and morphology of the particles are shown. Yttria and alumina were not found in separate particles but the elements constituting them (i.e., Y, Al, O) are either in solid solutions in the crystalline particles or dispersed within the amorphous portion of the powder. Dense materials were obtained by pressureless sintering at 1750 °C. Microstructure and composition of silicon nitride grains and of grain boundary phases are analyzed and discussed. When compared to a micro-sized Si₃N₄, nanoindentation tests clearly revealed the inverse Hall Petch relation. The nanosize Si₃N₄ shows a Young’s modulus which is almost independent on the peak load. PACS 81.05.J,M; 81.40; 81.05.Y; 81.05.J; 46.30.P     

Scanning probe oxidation of Si3N4 masks for nanoscale lithography,micromachining, and selective epitaxial growth on silicon

For studying the physical, chemical, and electronic properties of ultrasmall man-made structures, the major challenge is to fabricate highly uniform structures and control their positions on the nanometer length scale. Local oxidation of metals and semiconductors using a conductive-probe atomic force microscope (AFM) or other scanning probe microscopes in air at room temperature has emerged as a simple and universal method for this purpose. Here the uses of scanning probe oxidation of Si₃N₄ masks for performing nanolithography, nanomachining, and nanoscale epitaxial growth on silicon are reviewed. The three most unique features of this approach are presented: (1) exceptionally fast oxidation kinetics using silicon nitride masks (∼30 μm/s at 10 V for a ∼5-nm-thick film); (2) selective-area anisotropic etching of Si using a Si₃N₄ etch mask; and (3) selective-area chemical vapor deposition of Si using a SiO₂/Si₃N₄ bilayer growth mask.     

Wigner crystallization of electrons and holes in amorphous silicon nitride. Antiferromagnetic ordering of localized electrons and holes as a result of a resonance exchange interaction

The predicted quantitative relation between the density and trapping cross section of traps in Si₃N₄ and the Coulomb repulsion radius in the Wigner crystallization of carriers in localized states is observed experimentally. The absence of ESR for localized electrons and holes in Si₃N₄ is interpreted on the basis of a model of a resonance exchange interaction of electrons on account of tunneling via localized states. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 489–494 (10 October 1996)     

Pulsed CO2 laser-driven production of ultrafine silicon,silicon carbide,silicon nitride and silicon oxynitride powders

Summary Ultrafine Si, Si₃N₄, SiC and silicon oxynitride powders have been produced by irradiating gas-phase reactants by means of a CO₂ laser. The mechanism of SiH₄ CO₂ laser-induced absorption and dissociation is discussed on the basis of the results of the spectral and time-resolved measurement of fragment chemiluminescence. The role played by the SiH₂ radical in the powder formation is investigated. The quality of Si, Si₃N₄, SiC and silicon oxynitride powders is checked by means of several off-line diagnostics (IR spectroscopy, X-ray diffraction at wide and small angle, BET analysis). The possibility of controlling powder stoichiometry and doping from the gas-phase reactant concentration is discussed.     

Stuffed fullerene structures for medium-sized silicon clusters

The structural properties of medium-sized silicon clusters (Si₄₀, Si₄₅ and Si₅₀) have been studied using an unbiased global genetic algorithm search incorporated with a tight-binding model, followed by gradient-corrected density functional calculations. Stuffed fullerene cages are obtained as energetically favorite structures. The stuffing/cage ratio (m/n for Si_m@Si_n) can be understood by a space filling picture. The present results, along with our recent works on Si_N (N=27-39) clusters [20], suggest that stuffed fullerene cages are the preferred structural growth pattern of medium-sized silicon clusters.     

Effect of tellurium on electrical and structural properties of sintered silicon nitride ceramics

The effects of tellurium (Te) additives on electrical conductivity, dielectric constant and structural properties of sintered silicon nitride ceramics have been studied. Different amounts of Te (10% and 20%) were added as sintering additives to silicon nitride ceramic powders and sintering was performed. Microstructure and composition were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The electrical conductivity and dielectric constant (ε′) increase exponentially with temperature greater than 800 K. The electrical conductivity and dielectric constant increase but activation energy decreases from 0.72 to 0.33 eV with the increase of Te concentration. However, the conductivity increases five orders of magnitude at the concentration of 10% of Te in Si₃N₄. As the Te concentration increases the sintered silicon nitride ceramics become denser. These types of samples can be used as high temperature semiconducting materials.     

氮化硅薄膜的微结构

利用TEM,STM和PDS显微光度计研究了ECR-PECVD技术制备的Si₃N₄薄膜的微结构.结果表明：在较低沉积温度下，ECR-PECVD制备的Si₃N₄薄膜是一种纳米α-Si₃N₄薄膜，其晶粒粒度在14—29nm间，而且这种薄膜具有较好的表面平整度.初步分析了ECR-PECVD制备的Si₃N₄在较低沉积温度下形成晶态薄膜的机理. 关键词：     

Temperature effect on deposition rate of silicon nitride films

Temperature effects on deposition rate of silicon nitride films were characterized by building a neural network prediction model. The silicon nitride films were deposited by using a plasma enhanced chemical vapor deposition system and process parameter effects were systematically characterized by 2⁶⁻¹ fractional factorial experiment. The process parameters involved include a radio frequency power, pressure, temperature, SiH₄, N₂, and NH₃ flow rates. The prediction performance of generalized regression neural network was drastically improved by optimizing multi-valued training factors using a genetic algorithm. Several 3D plots were generated to investigate parameter effects at various temperatures. Predicted variations were experimentally validated. The temperature effect on the deposition rate was a complex function of parameters but N₂ flow rate. Larger decreases in the deposition rate with the temperature were only noticed at lower SiH₄ (or higher NH₃) flow rates. Typical effects of SiH₄ or NH₃ flow rate were only observed at higher or lower temperatures. A comparison with the refractive index model facilitated a selective choice of either SiH₄ or NH₃ for process optimization.