Silicon Crystal Lattice Research Articles

Structure and composition of silicon microarrays subjected to cyclic insertion and extraction of lithium

The silicon anodes for lithium-ion batteries subjected to cyclic tests of variable duration are studied by electron microscopy, energy-dispersive X-ray analysis, and Raman scattering. It is shown that the discharge capacity of electrodes based on macroporous silicon degrade due to the fracture of silicon walls and the formation of a Si-Li amorphous phase. Both effects arise early on testing. The number of cracks and the degree of disorder of the silicon crystal lattice are found to grow with the number of lithiation cycles and be nonuniformly distributed along the height of the walls. Namely, lithium is incorporated largely into the upper part of the structure adjacent to the separator. The disorder degree of the crystal lattice in the lithiated anodes is compared with that in standard amorphous silicon by analysis of the Raman spectra.

Room-Temperature Near-Infrared Electroluminescence from Boron-Diffused Silicon Pn-Junction Diodes

Silicon pn junction diodes with different doping concentrations were prepared by boron diffusion into Czochralski (CZ) n-type silicon substrate. Their room-temperature near-infrared electroluminescence (EL) was measured. In the EL spectra of the heavily boron doped diode, a luminescence peak at ~1.6 m (0.78 eV ) was observed besides the band-to-band line (~1.1eV) under the condition of high current injection, while in that of the lightly boron doped diode only the band-to-band line was observed. The intensity of peak at 0.78 eV increases exponentially with current injection with no observable saturation at room temperature. Furthermore, no dislocations were found in the cross-sectional transmission electron microscopy image, and no dislocation-related luminescence was observed in the low-temperature photoluminescence spectra. We deduce the 0.78 eV emission originates from the irradiative recombination in the strain region of diodes caused by the diffusion of large number of boron atoms into silicon crystal lattice.

Oxygen precipitation in 1020 cm−3 germanium-doped Czochralski silicon

We have investigated the effects of germanium (Ge)-doping at the level of 1020 cm−3 on oxygen precipitation (OP) behaviors in Czochralski (CZ) silicon subjected to different low-high two-step anneals without or with prior high temperature rapid thermal processing (RTP). It is found that Ge-doping remarkably suppresses OP in CZ silicon without prior RTP. However, Ge-doping significantly enhances OP in CZ silicon with prior RTP. The suppressed OP in the case of the absence of prior RTP is primarily due to the fact that the 1020 cm−3 Ge-doping introduces compressive strain into silicon crystal lattice, which increases the critical size of oxygen precipitate nuclei for a given nucleation temperature. Moreover, it is revealed that the 1020 cm−3 Ge-doping facilitates the formation of vacancy-oxygen (V-O) complexes and may introduce Ge-V-O complexes in CZ silicon during high temperature RTP. More vacancy-related complexes in CZ silicon not only reduce the critical size of oxygen precipitate nuclei but also provide more precursors for oxygen precipitate nucleation. Therefore, the 1020 cm−3 Ge-doping enhances OP in CZ silicon subjected to the two-step anneals following high temperature RTP.

Epitaxial growth of hexagonal silicon polytypes on sapphire

The formation of a single-crystal silicon polytype is observed in silicon-on-sapphire structures by high-resolution transmission electron microscopy. The appearance of inclusions with a structure different from that of diamond is attributed to the formation of strong-twinning regions and the aggregation of stacking faults, which form their own crystal structure in the crystal lattice of silicon. It is demonstrated that the given modification belongs to the 9R silicon polytype.

Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.

Measurements of CD and sidewall profile of EUV photomask structures using CD-AFM and tilting-AFM

Accurate and traceable measurements of critical dimension (CD) and sidewall profile of extreme ultraviolet (EUV) photomask structures using atomic force microscopes (AFMs) are introduced in this paper. An instrument complementarily applied with two kinds of AFM techniques, the CD-AFM and the tilting-AFM, has been developed. High measurement stability of the instrument is demonstrated, for instance, the long-term CD stability is better than 1 nm over 500 successive measurements over 55 h. To traceably calibrate the effective tip geometry, transmission electron microscopes-based method is applied, which uses either the silicon crystal lattice or the structure pitch value calibrated by metrological AFMs as an internal scale. Several grating patterns with different nominal CDs and line/space ratios of an EUV photomask have been measured using the developed methods. A data evaluation method with considered higher order tip effect due to the non-vertical sidewall is introduced. Detailed measurement results of a test EUV photomask, such as middle CD, left and right sidewall angle, feature height, line edge roughness and edge profiles are given. Finally, the AFM results are compared to that of a PTB EUV scatterometer. The comparison of the middle CD yields a linear relation within a spread of only about ±2 nm and an offset of the absolute values below 3 nm. For the sidewall angle, both methods yield consistent results within a range of about 2°.

Elimination of Curvature in Microelectromechanical-System Membrane

This paper describes the correlation between microelectromechanical-system (MEMS) membrane curvature and implanted argon in a microelectromechanical-system membrane. When a free-standing silicon membrane, fabricated through ashing of an organic film, is cleaned by exposure to argon plasma to remove the oxidized surface, the membrane is curved uniformly. The curvature is released by annealing. Total-reflection X-ray fluorescence analysis before/after annealing reveals that argon, which is implanted into the crystal lattice of silicon by argon plasma exposure, is desorbed by annealing. This analysis also indicates that there is a linear correlation between the curvature change and implanted argon.

Deformation and Restoration of Shape in Microelectromechanical System Membrane

This paper investigates whether there is a relationship between the curvature of a microelectromechanical-system (MEMS) membrane and the amount of argon (Ar) implanted in it. When a freestanding silicon membrane, fabricated through ashing of an organic sacrificial layer, is cleaned by exposure to Ar plasma to remove the superficial oxide, the membrane is curved uniformly. The curvature is released by annealing. An analysis of total-reflection X-ray fluorescence (TXRF) before and after annealing reveals that Ar, which is implanted into the crystal lattice of silicon by Ar plasma exposure, is desorbed by annealing, thereby restoring the original shape. This analysis also indicates that there is a linear relationship between the change in curvature and the concentration of implanted Ar.

Influence of total beam current on HRTEM image resolution in differentially pumped ETEM with nitrogen gas

Environmental transmission electron microscopy (ETEM) enables the study of catalytic and other reaction processes as they occur with Angstrom-level resolution. The microscope used is a dedicated ETEM (Titan ETEM, FEI Company) with a differential pumping vacuum system and apertures, allowing aberration corrected high-resolution transmission electron microscopy (HRTEM) imaging to be performed with gas pressures up to 20 mbar in the sample area and with significant advantages over membrane-type E-cell holders. The effect on image resolution of varying the nitrogen gas pressure, electron beam current density and total beam current were measured using information limit (Young's fringes) on a standard cross grating sample and from silicon crystal lattice imaging. As expected, increasing gas pressure causes a decrease in HRTEM image resolution. However, the total electron beam current also causes big changes in the image resolution (lower beam current giving better resolution), whereas varying the beam current density has almost no effect on resolution, a result that has not been reported previously. This behavior is seen even with zero-loss filtered imaging, which we believe shows that the drop in resolution is caused by elastic scattering at gas ions created by the incident electron beam. Suitable conditions for acquiring high resolution images in a gas environment are discussed. Lattice images at nitrogen pressures up to 16 mbar are shown, with 0.12 nm information transfer at 4 mbar.

Laser Processed Black Silicon for Photovoltaic Applications

We present a femtosecond laser pulse process that induces a texture-like surface structure on silicon wafers and optionally incorporates sulfur into the silicon lattice for emitter formation depending on the processing atmosphere. Such laser processed Black Silicon provides an easily adjustable surface roughness for good light trapping in silicon solar cells. The structure is independent of the silicon crystal orientation and is easily applied on one wafer side only. A sulfur emitter can be formed within the laser structuring process, and allows electric current extraction from a solar cell structure manufactured from this material. Then the advantage is that no further emitter formation step like diffusion is necessary compared to other Black Silicon solar cell approaches, where the Black silicon is created wet chemically. By incorporating sulfur in the silicon crystal lattice, we can show that this Black Silicon absorbs in the infrared wavelength regime. This characteristic can potentially be used to better exploit the energy in the sun spectrum. We manufacture a laser processed Black Silicon solar cell prototype without any emitter diffusion step and achieve the highest efficiency of 4.5% reported for this cell type.

Influence of mechanical defects on the crystal lattice of silicon

AbstractTo examine the impact of mechanical defects on the crystal lattice of silicon, controlled damage was applied to silicon wafers by a nanoindendation method. With increasing loads of 1, 5 and 50 N, the area with micro‐cracks and strain around the indents increases. The damage is characterised by high resolution diffractometry using a conventional X‐ray tube. Spatially resolved rocking curves were recorded across the indents and analysed with respect to full width at half maximum. From reciprocal space maps the amount of strain and tilt around the indents is separated. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study on Solid Phase Crystallization of Silicon Films Deposited on Different Substrates

Porous silicon were prepared by electrochemical corrosion. Undoped and boron doped silicon films were deposited on quartz substrate、porous silicon and silicon substrate by PECVD,and were solid phase crystallized at different temperature and different hours. The microstructure of films before and after annealing were studied by Raman and XRD. The results show that:the crystallization of films deposited on porous silicon and monocrystalline silicon substrate are better than quartz substrate; The substrate which has silicon crystal lattice play an important role of seed crystal in the solid phase crystallization, the same grain orientation film can be grown on certain condition.

Geometric optimization of van der Pauw structure based MEMS pressure sensor

This paper characterizes a piezoresistive sensor under variations of both size and orientation with respect to the silicon crystal lattice for its application to MEMS pressure sensing. The sensor to be studied is a four-terminal piezoresistive sensor commonly referred to as a van der Pauw (VDP) structure. It is observed that the sensitivity of the VDP sensor is over three times higher than the conventional filament type Wheatstone bridge resistor. With MEMS devices being used in applications which continually necessitate smaller size, characterizing the effect of size and orientation of a VDP structure on the performance of a MEMS pressure sensor is important. In this paper, the effect of relative size and misalignment of the VDP sensor on the sensitivity is investigated using a coupled piezoresistive/stress finite element model. The mode is developed to simulate the full field stress over the deformed diaphragm in which the VDP is diffused. The change in resistivity of the VDP is then analyzed to predict the sensitivity of the VDP structure. Sensor size, position relative to the diaphragm, and angular misalignment of the VDP were varied to determine a theoretical result for the dependence of VDP output on those parameters. It is determined that the performance of the sensor is strongly dependent only on the longitudinal position of the sensor on the diaphragm, and is relatively tolerant of other errors in the manufacturing process such as transverse position, sensor depth, and orientation angle.

Spreading resistance and compensation of charge carriers in ferromagnetic silicon implanted with manganese

Profiles of impurity distribution and spreading resistance have been studied in the layers of ferromagnetic silicon obtained by implantation of Mn (or Co). Standard wafers of n- and p-Si with a high or low electrical conductivity were implanted with Mn ions with the dose (1−5) × 1016 cm−2. It is found that, as a result of postimplantation annealing in vacuum for 5 min at 850°C, Mn manifests itself as an amphoteric impurity and compensates acceptors in high-resistivity p-Si and donors in low-resistivity n-Si. It is shown that only an insignificant fraction of Mn ions (1–2%) is electrically active and is involved in compensation. The magnitude of compensation is used to determine energies of the levels E c − 0.12 eV for n-Si and E v + 0.32 eV for p-Si; these levels are attributed to Mn ions at interstitial sites in the silicon crystal lattice, i.e., (Mn i )−/0 and (Mn i )+/++, respectively.

Analysis of the dipole matrix elements of electronic optical transitions in the P 2 + /Si system

This study is concerned with a singly ionized pair of phosphorus donors in the silicon crystal lattice. The results of numerical calculations of the energy spectrum and dipole matrix elements in such a system are reported. The conditions, in which the P2+/Si system can be used in the implementation of quantum operations with resonance laser pulses, are determined. Estimation of the time of such operations yields ∼10 ps.

Properties of a silicon surface exposed to nanosecond laser-radiation pulses

Results of the use of nanosecond laser pulses in the technology of production of very-large-scale integration circuits are presented. It is shown that, depending on the conditions of processing of silicon by these pulses, they can avoid mechanical failure of the silicon crystal lattice and form a gettering layer that cleans the silicon from impurities.

SILICON'S BUILDING BLOCK SYNTHESIZED

THE SMALLEST DISCRETELY defined repeat unit that can be plucked from the silicon crystal lattice has been synthesized as an independent molecule by a team of Austrian chemists ( Science 2005 , 310 , 825). Sila-adamantane, as the new compound is called, is a tricyclic Si 10 cluster with pendant methyl and trimethylsilyl groups. The molecule is anticipated to help scientists better understand how the properties of silicon transition from the molecular level to the bulk solid. Sila-adamantane was synthesized by Jelena Fischer, Judith Baumgartner, and Christoph Marschner of Graz University of Technology. The compound has the same structure as adamantane, the carbon compound that serves as the repeat unit in diamond, one of carbon's structural allot ropes. Marschner's group had previously synthesized a bicycloheptasilane compound. To make sila-adamantane, the researchers derivatized the heptasilane by attaching a cyclohexylsilanyl group. This substituted bicyclic precursor was then treated with AlCl 3 , whic...

Germanium in Czochralski Silicon

The behaviors of isovalent impurities doped in Czochralski (CZ) silicon crystal have attracted considerable attention in recent years. In this article, a review concerning recent processes in the study about germanium in CZ silicon is presented. The disturbance of silicon crystal lattice in and the influence on the mechanical strength due to germanium doping is described. Oxygen related donors, oxygen precipitation and voids defects in germanium doped Czochralski (GCZ) silicon has been demonstrated in detail. In addition, the denuded zone formation and the internal gettering technology of GCZ silicon is also discussed.

Channeling of high-energy particles in a multi-wall nanotube

Channeling of high-energy particles in straight and bent multi-wall nanotubes (MWNT) has been studied in computer simulations and compared to the channeling properties of single-wall nanotubes (SWNT) and bent crystal lattices. It is demonstrated that MWNT can efficiently channel positively-charged high-energy particles trapped between the walls of MWNT. Bending dechanneling in MWNT has been computed as a function of the particle momentum to nanotube curvature radius ratio, pv/R. It is found that a bent MWNT can steer a particle beam with bending capabilities similar to those of bent silicon crystal lattice and to those of best (i.e., the narrowest) SWNT. In view of channeling applications at particle accelerators, MWNT appear favored as compared to SWNT, because MWNT can be produced quite straight (and in aligned array), while SWNT is typically very curved, thus posing a severe problem for channeling applications. Therefore, we suggest that MWNT provide a better candidate for channeling than SWNT.

Transformation of the Defects of Gold in Silicon: Structural Phase Transition

Based on the experimental data on the specific heat and photoconductivity of silicon doped with gold, the possible mechanisms of transformation of the impurity centers of gold in the crystal lattice of silicon and accordingly phase transitions are discussed.