There has been a great interest in the strained Si CMOS technology lately, especially the modification of band structures which provides a theoretical basis for the design of the high-speed and high-performance devices and circuits. Calculations were performed on the band structures in strained Si/(111)Si1-xGex(0≤x≤0.4) by the first-principle pseudopotential approach of the plane wave based upon the density functional theory. It was found that the conduction band (CB) edge is characterized by the six valleys all the same, that valence band (VB) edge degeneracies are partially removed and that the electron mass in CB is unaltered under strain while the hole mass decreases along the ［100］ direction with increasing x. In addition, the fitted dependence of bandgap on x are in good agreement with KP theoretical calculation, from which the quantitative data supply valuable references to the devices design.
Superplastic forming/diffusion bonding(SPF/DB) has been widely used in the automotive and aerospace industry since it has great advantages to produce very light and strong components. Finite element method(FEM) is used to model the SPF/DB process of 3-sheet sandwich panel to predict the pressure-time curve and to analyze the process parameters. In order to eliminate defects of the part, a new pressurization scheme is proposed. Contrary to the conventional one-step pressurization, which causes the folding at the DB joint, two-step pressurization can eliminate the folding. Effect of pressurization cycle was investigated by using FE analysis and proper pressurization cycle is proposed.
As an indirect band gap semiconductor, germanium (Ge) can be transformed into a direct band gap semiconductor through some specific modified methods, stress, and alloying effect. Direct band gap-modified Ge semiconductors with a high carrier mobility and radiation recombination efficiency can be applied to optoelectronic devices, which can improve the luminous efficiency dramatically, and they also have the potential application advantages in realizing monolithic optoelectronic integration (MOEI) and become a research hotspot in material fields. Among the various implementations of Ge band gap-type conversion, the related methods that are compatible with the Si process are most promising. It is such a method to etch around the Ge epitaxial layer on the Si substrate and introduce the biaxial tensile stress by SiGe selective filling. However, the influence of the width of the epitaxial layer, Ge composition, and Ge mesa region width on strain distribution and intensity is not clear yet. Accordingly, a finite element stress model of the selective epitaxy-induced direct band gap Ge scheme is established to obtain the material physical and geometric parameters of the Si 1− x Ge x growth region. The result of finite element simulation indicates when the Si 1− x Ge x epitaxial layer is 150–250 nm wide and the Ge composition is 0.3∼0.5, Ge mesa with 20–40 nm in width can be transformed into direct band gap semiconductors in the depth of 0–6 nm. The theoretical results can provide an important theoretical basis for the realization of subsequent related processes.
A band edge model in (101)-biaxial strained Si on relaxed Si1-xGex alloy,or monoclinic Si (m-Si),is presented using the k·p perturbation method coupled with deformation potential theory.Results show that the ［001］,［001］,［100］,［100］ valleys constitute the conduction band (CB) edge,which moves up in electron energy as the Ge fraction (x) increases.Furthermore,the CB splitting energy is in direct proportion to x and all the valence band (VB) edges move up in electron energy as x increases.In addition,the decrease in the indirect bandgap and the increase in the VB edge splitting energy as x increases are found.The quantitative data from the models supply valuable references for the design of the devices.
Abstract We fabricated Co 3 O 4 catalysts with different spatial structures, such as zero‐dimensional (nanoparticles), one‐dimensional (nanorods), two‐dimensional (nanoplates), and three‐dimensional (mesoporous and microporous) structures, for methane combustion. The Co 3 O 4 catalysts with different dimensional architectures demonstrated different activities for the breaking of the C−H bond of methane. In particular, Co 3 O 4 with 2 D structure gave rise to the highest activity among all the samples, in which methane could be initially ignited below 200 °C and completely converted to CO 2 at 375 °C. This activity is attributed to the collective contribution from all the exposed high‐index planes of 2 D Co 3 O 4 and to more surface‐active species being formed on 2 D Co 3 O 4 .
Based on the analysis of Poly-Si1-xGex gate work function and by solving Poisson equation, the models of vertical electric field and potential distribution in strained Si NMOSFET with Poly-Si1-xGex gate are obtained; threshold voltage model and the gate depletion thickness and it's normalization model are established in strained Si NMOSFET based on the above results, with the gate depletion effect of Poly-Si1-xGex taken into account. Then the influences of device geometrical and physical parameters of device especially the Ge fraction on Poly-Si1-xGex gate depletion thickness are investigated. Furthermore, the effect of gate depletion thickness on threshold voltage is analyzed. It shows that the poly depletion thickness decreases with the increases of Ge fraction and gate doping concentration, while it increases with the increase of substrate doping concentration. Furthermore, the threshold voltage increases with the increase of gate depletion thickness. The results can provide theoretical references to the design of strained Si devices.
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