Disordering and annealing of a Si surface under low-energy Si bombardment

Abstract

We simulated the bombardment of Si(100)(2 × 1) by Si atoms using molecular dynamics. The kinetic energies of the projectiles were 100 and 50 eV. To model the Si–Si-interactions the empirical potential of Stillinger and Weber with the two body part of the potential splined to the universal potential was used. A geometric criterion based on the Lindemann radius was defined to study damage in the Si target. We observed clusters of disordered Si atoms in the target induced by the bombardment. Large clusters of about 50 atoms are formed in the beginning of the bombardment; they shrink and decay into smaller clusters until and equilibrium cluster size of about 10 atoms is reached. Upon annealing at elevated temperature the disordered zones dissolve into point defects.     

Theoretical analysis of thermal rectification in a bulk Si/nanoporous Si device

We present a theoretical analysis of thermal rectification in a porous Si/bulk Si device, taking into account ballistic effects in phonon-pore collisions when phonon mean free path is much longer than the radius of the pores. Starting from an approximate analytical expression for the effective thermal conductivity of porous Si, we obtain the thermal rectifying coefficient of the device as a function of porosity, pore size, temperature interval, and relative lengths of porous and bulk samples.     

Rainbows with a Si thin crystal

This study is devoted to the transmission of Ne¹⁰⁺ ions through a Si thin crystal. The ion energy is 60 MeV and the crystal thickness is varied from 159 to 478 atomic layers, i.e. within the first rainbow cycle. The analysis is performed by the theory of crystal rainbows. The angular distribution of the transmitted ions is generated by the computer simulation method. Then, the rainbow lines in the scattering angle plane are determined. These lines ensure the full explanation of the angular distribution. Received 11 May 2000     

Optical modulator based on a Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice structure

An optical modulator is designed and fabricated based on a Si_0.75Ge_0.25/Si/Si_0.5Ge_0.5 asymmetrical superlattice structure. The device comprises a p-i-n diode made on the asymmetrical superlattice integrated with a 920-μm-long Fabry-Perot (F-P) cavity. Parameters of the rib waveguide are designed to satisfy only the fundamental-TE mode transmission. Here, 65 and 40-pm red shifts of the peak resonant were measured under the applied bias of 2.5 and ?32.0 V, respectively. The analysis shows that, besides the thermal-optical and plasma dispersion effects, the Pockels effect also contributes to such a peak shift. The corresponding calculated effective Pockels coefficient is about 0.158 pm/V.

     

第一性原理研究应变Si/(111Si1-xGex能带结构

基于密度泛函理论框架的第一性原理平面波赝势方法对双轴应变Si/(111)Sil1-xGex(x=0.1-0.4)的能带结构进行了研究,结果表明:导带带边六度简并没有消除;应变部分消除了价带带边的简并度;导带带边能量极值k矢位置和极值附近可由电于有效质量描述的能带形状在应变条件下几乎小变;价带极大值附近可由空穴有效质量描述的能带形状随着x有规律地变化.此外,给出的禁带宽度与x的拟合关系同KP理论计算的结果一致,该量化数据对器件研究设计可提供有价值的参考.     

Formation mechanism of one-dimensional Si islands on a H/Si(001) surface

The formation mechanism of one-dimensional Si islands on a H/Si(001)-(2x1) surface is studied using scanning tunneling microscopy/spectroscopy and first-principles calculations. We observed that one-dimensional islands that are made from dimer chains are formed at the initial growth stages similar to the bare Si(001) surface. It is found that the number of odd-numbered dimer chains is larger than that of even-numbered dimer chains. We propose the growth processes of the two types of growth edges to explain the observation.     

一种新型Si/SiGe/Si双异质结PIN电学调制结构的异质结能带分析

PIN结构是电光调制器中常见的一种电学调制结构, 该结构中载流子注入效率直接影响着电光调制器的性能. 在前期的研究中, 我们在SOI材料的基础上提出了一种新型Si/SiGe/Si双异质结PIN电学调制结构, 可以有效提高载流子注入效率, 降低调制功耗. 为了进一步研究这种新型调制器结构的调制机理, 本文从单异质结能带理论出发, 定量分析了该新型结构中双异质结的势垒高度变化, 给出了双异质结势垒高度的定量公式, 将新型结构与SiGe-OI和SOI两种PIN电学调制结构进行能带对比, 分析了该新型结构载流子注入增强的原因, 最后模拟了新型结构的能带分布, 以及能带和调制电压与注入载流子密度的关系, 并与SiGe-OI和SOI两种PIN电学调制结构进行对比发现, 1 V调制电压下, 新型结构的载流子密度达到了8× 10¹⁸cm^-3, 比SOI 结构的载流子密度高了800%, 比SiGe-OI结构的载流子密度高了340%, 进一步说明了该新型结构的优越性, 并且验证了理论分析的正确性.     

Surface-phonons at a free-111-surface of Si

In a crystal with a free surface the translational symmetry in one direction is raised. In this case it is possible to reduce the equation of motion of the crystal to a form which is analogous to the equation of motion of a semi-infinite generalized linear chain. In this picture the surface-phonons correspond to boundary vibrations of the chain. Methods to calculate the frequencies and the “damping” constant of the surface-phonons are shown. If the surface exhibits a symmetric structure it is possible to classify the frequencies according to the irreducible representations of a subgroup of the surface-space-group. Model-calculations are performed for a free Si-111-surface using a six-parameter potential (fitted to dispersion curves). The change of the force constants near the surface is considered and fitted to the experiment of Ibach (ν=13.3×10¹² sec^?1). With the obtained weakening of the potential near the surface, dispersion-curves for surface-phonons are calculated.     

Self-catalytic growth of horizontal and straight Si nanowires on Si substrates using a sputter deposition technique

We report on the growth of horizontal and straight Si nanowires (NWs) on Si substrate using sputter deposition of the Si layer followed by thermal annealing at 1000 °C and above. The growth of horizontal NWs was achieved without the use of any metal catalyst. Uniform cylindrical shaped Si NWs with a diameter in the range of 50–60 nm and a length of up to 8 μm were synthesized. The as-synthesized Si NWs have a Si core covered with a thin amorphous native oxide layer, as revealed by high resolution transmission electron microscopy. The aspect ratio of these Si NWs is in the range of 100–160. Micro-Raman studies on the NWs reveal a tensile strain on the Si NW core due to presence of a thin oxide layer. From the Raman shift, we calculate a strain of 1.0% for the catalyst free Si NW. FTIR analysis indicates the presence of interstitial oxygen atoms in the Si NWs, as expected from oxidation of Si NWs. For comparison, metal catalyst (Au) assisted Si NWs have also been grown on Si(100) substrate by a similar process. These NWs have a similar diameter and a marginally higher aspect ratio. A model for the growth mechanism of horizontal NWs is presented. This represents one of the first examples of direct horizontal growth of straight Si NWs on commonly used Si substrates suitable for nanoelectronic device fabrication.     

Stark broadening parameters of Si I,Si II and Si III lines

Spectral lines emited by first three ionisation species of silicon were studyed in a wide range of plasma parameters. The silicon was present as an impurity in the argon plasma created in an electromagneticT tube. Four various condenser bank energies give the plasma in a range of temperatures 8700 to 16400°K and electron concentrations 2.95·10¹⁷ cm^?3to 5.6·10¹⁷ cm^?3. Measured line widths and shifts were compared with theories of Griem [1, 2] and Sahal Brechet [3, 10]. The agreement is reasonably good, the measured values are in general smaller than calculated ones.     

Thin-film formation of Si clathrates on Si wafers

In this study, we prepared Si clathrate films (Na₈Si₄₆ and Na_xSi₁₃₆) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10⁻² Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na₈Si₄₆ and Na_xSi₁₃₆ using the appropriate crystalline orientation of Si substrates.     

On optimum designs of a RCE Si/SiGe/Si MQW photodetector for long wavelength applications

In the present paper, performance analysis of a resonant-cavity-enhanced Si/Si_1–y Ge _y /Si multiple quantum well photodetector has been carried out. The effects of material parameters of active Si_1–y Ge _y layers and carrier trapping by the potential barriers at the heterointerfaces of Si/Si_1–y Ge _y /Si quantum wells on the bandwidth (BW) and Responsivity of the photodetector have been investigated using numerical simulation. Results on possible optimum designs of the photodetector have been suggested to maximize BW-quantum efficiency product.     

The evolution of a microstructure on Si by a femtosecond laser

Femtosecond laser micromaching silicon is investigated by a Ti:sapphire laser (800 nm, 1 kHz) with a pulse duration of 130 fs. It is investigated that the result is affected by fluences at a different number of pulse. In the experiment, we have observed the periodic surface structure such as microholes, and found that the direction of the array holes was parallel to the laser polarization direction. This result has potential application in the fabrication of two-dimensional photonic crystals. We have determined the optimal conditions for producing these surface structures. At the same time, when we change the fluence and the pulse number, the ripples and the columns emerge. If the pulse number remains unchanged, we also investigated the evolution of a crater at a different pulse fluence. The microholes will become regular cracks on the outer irradiation area, and the ripples will gradually disappear. But, the column structures will appear. At a higher fluence, ripples only appear when the number of pulses (N) is less than 200 and a column structure exists at the center region when N is above 600.     

Read—out of a read—only super—resolution optical disc with a Si mask

A novel read-only super-resolution optical disc structure (substrate/mask layer/dielectric layer) is proposed in this paper. By using a Si thin film as the mask layer, the recording pits with a diameter 380nm and a depth 50nm are read out on the dynamic measuring equipment; the laser wavelength α is 632.8nm and the numerical aperture is 0.40. In the course of reproduction, the laser power is 5mW and the rotation velocity of the disc is 4m·s^-1. The optimum thickness of the Si thin film is 18nm and the signal-to-noise ratio is 32dB.     

Alpha-induced fragmentation of 28Si in a statistical model

Within the context of a statistical model, that incorporates final-state interaction between a pair of fragments, we have calculated the energy spectra associated with the production of different isobaric pairs as a function of their lab kinetic energy and isobaric and elemental distributions of nuclei produced in the ⁴He$ + $²⁸Si reaction at cm incident energies of 102.7, 173.7, 300, 500, and 1000MeV. Double differential cross-section of isobars 16, 20, and 24 as a function of their lab kinetic energies at 30^° and the same for isobar 24 at 10^°, 30^°, 60^°, and 90^° have been calculated at cm incident energies of 102.7 and 173.7MeV and compared with the data of Woo et al. Calculated yields follow the trend of the data at each angle, and calculated angular distributions also reproduce the general trend of the observed ones. A key feature of the model is that it allows for fragments to be emitted in ground states as well as in excited states that are allowed by the conservation of energy. The analysis establishes that the fragments are emitted in excited state. The excitation energies for A = 24 and 16 are deduced from the data. The observed angular distributions for A = 7, 12, 16, 20, 24, and 28 are well accounted for assuming them to be emitted in excited states. The relative production probabilities for different elements and isobars are energy dependent. The yields for unstable elements, ⁵Li, ⁸Be, and ²⁶Al, are found to be significant. The relative fragmentation probabilities of all allowed isotopic pairs have been presented.