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.     

Capturing properties of a threefold coordinated silicon atom in silicon nitride: Positive correlation energy model

The electronic structure and capturing properties of threefold coordinated silicon atoms (≡Si·) and the Si-Si bond in silicon nitride (Si₃N₄) were studied using the ab initio density functional theory. The results show that the previously proposed negative correlation energy (NCE) model is not applicable to Si₃N₄. The NCE model was proposed for interpreting the absence of the ESR signal for threefold coordinated silicon defects and suggested that an electron can transfer between two silicon defects. We proposed that the absence of this ESR signal is due to the creation of neutral diamagnetic Si-Si defects in Si₃N₄. This model offers the most fundamental theory for explaining the hole localization (memory) effect in silicon nitride.     

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).     

Electronic structure of TiO<Subscript>2</Subscript> rutile with oxygen vacancies: Ab initio simulations and comparison with the experiment

The electronic structure of TiO₂ rutile with oxygen vacancies, which is a promising insulator, has been analyzed. The ab initio density functional calculations, as well as the comparative analysis of the results obtained in the σ-GGA spin-polarized generalized approximation and those obtained by the σ-GGA + U method with allowance for Coulomb correlations of d electrons titanium atoms in the Hartree-Fock approximation for the Hubbard model, have been performed. It has been found that the effective electron mass in rutile is anisotropic and there are both light (m _e ^* = (0.6–0.8)m ₀, where m ₀ is the free-electron mass) and heavy (m _e ^* > 1m ₀) electrons, whereas holes in rutile are only heavy (m _e ^* ⩾ 2m ₀). It has been shown that the σ-GGA + U method gives a deep occupied level in the band gap and that an oxygen vacancy in rutile is an electron and hole trap.     

Low-Temperature Sputtered Ultralow-Loss Silicon Nitride for Hybrid Photonic Integration

Silicon-nitride-on-insulator (Si₃N₄) photonic circuits have seen tremendous advances in many applications, such as on-chip frequency combs, Lidar, telecommunications, and spectroscopy. So far, the best film quality has been achieved with low pressure chemical vapor deposition (LPCVD) and high-temperature annealing (1200°C). However, high processing temperatures pose challenges to the cointegration of Si₃N₄ with pre-processed silicon electronic and photonic devices, lithium niobate on insulator (LNOI), and Ge-on-Si photodiodes. This limits LPCVD as a front-end-of-line process. Here, ultralow-loss Si₃N₄ photonics based on room-temperature reactive sputtering is demonstrated. Propagation losses as low as 5.4 dB m⁻¹ after 400°C annealing and 3.5 dB m⁻¹ after 800°C annealing are achieved, enabling ring resonators with highest optical quality factors of > 10 million and an average quality factor of 7.5 million. To the best of the knowledge, these are the lowest propagation losses achieved with low temperature Si₃N₄. This ultralow loss enables the generation of microresonator soliton frequency combs with threshold powers of 1.1 mW. The introduced sputtering process offers full complementary metal oxide semiconductor (CMOS) compatibility with front-end silicon electronics and photonics. This could enable hybrid 3D integration of low loss waveguides with integrated lasers and lithium niobate on insulator.     

Formation of the buffer layer of silicon suboxides SiOx in the Si/SiO2 low-dimensional heterosystem after Si+ ion implantation: Si L2, 3 X-ray emission spectra

Nanosized heterostructures n-Si/SiO₂ with different thicknesses of the oxide film (20, 500 nm) after implantation by Si⁺ ions with energies of 12 and 150 keV have been investigated using Si L _{2, 3} X-ray emission spectroscopy (the Si 3d3s → Si 2p _{1/2, 3/2} electronic transition). The ion-beam modification of the interface has been revealed and studied for the heterostructure with a silicon dioxide thickness of 20 nm. An analysis of the Si L _{2, 3} X-ray emission spectra has demonstrated that the Si⁺ ion implantation leads to the self-ordering of the structure of the initially amorphous SiO₂ film 20 nm thick due to the effect of high doses. A mechanism of ion-beam modification of the insulator-semiconductor interface has been proposed. No substantial transformation of the atomic and electronic structures of the heterostructure with a silicon dioxide thickness of 500 nm has been revealed after the ion implantation.     

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.     

On mass corrections to the decay <Emphasis Type="Italic">P</Emphasis> → <Emphasis Type="Italic">l</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">l</Emphasis><Superscript>−</Superscript>

The Mellin-Barnes representation is used to improve the theoretical estimate of mass corrections to the width of a light pseudoscalar meson decay into a lepton pair, P → l ⁺ l ⁻. The full resummation of the terms ln(m _l ²/Λ²)(m _l ²/Λ²) ⁿ and (m _l ²/Λ²) ⁿ to the decay amplitude is performed, where m _l is the lepton mass and Λ ≈ m _ρ is the characteristic scale of the P → γ*γ* form factor. The total effect of the mass corrections for the e ⁺ e ⁻ channel is negligible and, for the μ⁺μ⁻channel, its order is of a few percent. The text was submitted by the authors in English.     

n-type conductivity in Si-doped amorphous AlN: an ab initio investigation

We report the electronic structure and topology of a heavily Si-doped amorphous aluminium nitride (Al_37.5Si_12.5N₅₀) using ab initio simulations. The amorphous Al_37.5Si_12.5N₅₀ system is found to be structurally similar to pure amorphous aluminium nitride. It has an average coordination number of about 3.9 and exhibits a small amount of Si–Si homopolar bonds. The formation of Si–Al bonds is not very favourable. Electronic structure calculations reveal that the Si doping has a negligible effect on the band gap width but causes delocalization of the valence band tail states and a shift of the Fermi level towards the conduction band. Thus, amorphous Al_37.5Si_12.5N₅₀ alloys show n-type conductivity.     

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.     

N+BF<Subscript>2</Subscript> and N+C+BF<Subscript>2</Subscript> high-dose co-implantation in silicon

Nitrogen and boron BF₂, and nitrogen, carbon, and boron BF₂ high-dose (6×10¹⁶–3×10¹⁷ cm^-2) co-implantation were performed at energies of about 21–77 keV. Subsequent high-temperature annealing processes (600, 850, and 1200 °C) lead to the formation of three and two surface layers respectively. The outer layer mainly consists of polycrystalline silicon and some amorphous material and Si₃N₄ inclusions. The inner layer is highly defective crystalline silicon, with some inclusions of Si₃N₄ too. In the N+B-implanted sample the intermediate layer is amorphous. Co-implantation of boron with nitrogen and with nitrogen and carbon prevents the excessive diffusivity of B and leads to a lattice-parameter reduction of 0.7–1.0%. Received: 10 January 2002 / Accepted: 30 May 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. Fax: +34-91/3974895; E-mail: Lucia.Barbadillo@uam.es     

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.     

Oscillations of the magnetoresistance in an inclined magnetic field for MIS structures on (100) silicon with a high electron density

At electron densities N _S>6×10⁻² cm⁻²² a second series of oscillations, which are tentatively attributed to population of the second energy subband, is observed in addition to the main series of Shubnikov-de Haas oscillations. A change in phase of the oscillations of the second series is observed at some angle of inclination α_e of the field. The measured value of α_e is used to calculate the ratio of the cyclotron mass to the effective g factor. The maximum possible cyclotron mass is also determined as m _H< 0.32m _e. On this basis it is concluded that the second series of oscillations is due to electrons which have an in-plane effective mass m*≈0.2m _e and which belong to the same valleys of the Fermi surface as in the case of the main oscillations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 136–140 (25 January 1998)     

α-, β-和γ-Si3N4 高压下的电子结构和相变: 第一性原理研究

本文采用第一性原理框架下的赝势平面波方法结合振动类德拜模型研究了α,β和γ-Si₃N₄在高温下的点阵常数,弹性常数和弹性模量.研究发现三种同质异相体的体模量都很高.β-Si₃N₄在低温下表现出脆性,在高温下则表现出延展性.γ-Si₃N₄在低温和高温下都是脆性的共价化合物.β → γ 相变的相界斜率为正值,说明在较高温度时合成γ-Si₃N₄所需的压强也较高.α → γ 相变的相界可以表示成 P=16.29- 1.835-10^-2 T+9.33945-10^-5T²-2.16759-10^-7T³+2.91795-10^-10T⁴.本文还分析了Si₃N₄同质异相体在高压下的态密度和能带.在α-Si₃N₄中主要是Si-s, p和N-s,p的轨道杂化对晶体的稳定性起作用.α和β-Si₃N₄都具有Γ_V-Γ_C类型的间接带隙(分别是4.9~eV和4.4~eV)而γ-Si₃N₄具有直接带隙(3.9~eV). 研究还发现α-Si₃N₄和β-Si₃N₄的价带顶分别沿着Γ-M和Γ-A方向.本文的计算结果和已有的实验数据是一致的.     

Structure and optical properties of carbon films obtained by multipulse pulsed laser deposition

We have obtained carbon thin films on silicon and glass substrates with multipulse pulsed laser irradiation of graphite under vacuum (p ≈ 2.6 Pa) using a high-frequency series of nanosecond laser pulses (τ = 85 ns, λ = 1060 nm) with pulse repetition frequency f ≈ 10–20 kHz and laser power density q ≈ 15–40 MW/cm². We established the optimal laser power density and laser pulse repetition frequency for obtaining amorphous nanostructured diamond-like films.     

MINDO/3 calculation of the electronic structure of silicon nitride

The electronic structure of silicon nitride has been calculated by the semiempirical quantumchemical method MINDO/3 in the cluster approximation. The effect of cluster size and of boundary conditions on the partial density of one-electron states is analyzed. The results of the calculation are compared with experimental data on amorphous silicon nitride. The origin of a peak in the upper part of the valence band, which is seen in the SiL2,3 spectrum but not reproduced in the calculations is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1342–1347 (August 1997)     

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     

Controllable off-plane deflection of cantilevers for multiple scanning proximity probe arrays

The presented work reports the fabrication of 4×32 arrays of fully addressable proximity probes, which are initially and controllably off-plane deflected (bent). Such a deflection is required for the simultaneous approach and scanning of all cantilevers. It is realized by deposition of the silicon cantilevers with Si₃N₄ film inducing tensile stress. ANSYS simulations are used to calculate the off-plane deflection for different thickness of the cantilever and the Si₃N₄ layer and compared with experimentally obtained values. Cantilever arrays with set bending up to 50 μm, employing LPCVD silicon nitride film with a tensile stress of 750 MPa are fabricated.