Molecular dynamics in semiconductor physics

Molecular dynamics, which is a powerful method for studying both structural and dynamic properties of condensed matter, is employed as a “microscope for the motion of atoms”. Information about the motion of individual atoms that is difficult to obtain experimentally can be obtained using this method. Parallel computers with tera-flop speed and tera-byte memory will make it possible to perform hundreds of million particle simulations using empirical potential. Moreover, the macroscopic phenomena analyzed by continuum theory can be obtained by coarse-graining the atomic-level information provided by this approach. When considering the problem of data analysis, examples in semiconductor physics such as the implantation process are provided.     

Self-organization processes in semiconductor under photo-induced Gunn effect

Theoretical investigation of self-organization of non-equilibrium carriers system in n-GaAs under photo-stimulated Gunn effect was performed. It was shown that the behavior of carrier system could be controlled using incident light intensity resulting in different oscillation regimes. Results obtained allow us to predict application ranges for devices working on the phenomena investigated.     

Scheduling of wafer test processes in semiconductor manufacturing

This research focuses on solving a common wafer test scheduling problem in semiconductor manufacturing. During wafer testing, a series of test processes are conducted on wafers using computer-controlled test stations at various temperatures. The test processes are conducted in a specified order on a wafer lot, resulting in precedence constraints for the schedule. Furthermore, the assignment of the wafer lots to test stations and the sequence in which they are processed affects the time required to set up the test operations. Thus, the set-up times are sequence dependent. Four heuristics are developed to solve the test scheduling problem with the aim of minimizing the makespan required to test all wafers on a set of test stations. The heuristics generate a sorted list of wafer lots as a dispatching sequence and then schedule the wafer lots on test stations in order of appearance on the list. An experimental analysis and two case studies are presented to validate the proposed solution approaches. In the case studies, the heuristics are applied to actual data from a semiconductor manufacturing facility. For both case studies, the proposed solution approaches decrease the makespan by 23–45% compared with the makespan of the actual schedule executed in the manufacturing facility.     

表面光电压谱(SPS)在有机半导体材料研究中的应用

简要介绍了表面光电压谱（SPS）的几种常用测试方法和测试原理，通过典型实例说明了SPS技术在研究有机半导体电子结构，有机半导体薄膜的光电性能与制备方法的关系，半导体异质结性能等方面的应用，评述了SPS技术在研究酞菁氧钛／偶氮绿丹蓝复合材料的光电性能中发现的光伏极性反新现象，展望了SPS方法在有机半导体材料光电功能研究中的应用前景。     

Quantitative nanoscale surface voltage measurement on organic semiconductor blends

We report on the validation of a method based on Kelvin probe force microscopy (KPFM) able to measure the different phases and the relative work function of polymer blend heterojunctions at the nanoscale. The method does not necessitate complex ultra-high vacuum setup. The quantitative information that can be extracted from the topography and the Kelvin probe measurements is critically analysed. Surface voltage difference can be observed at the nanoscale on poly(3-hexyl-thiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blends and dependence on the annealing condition and the regio-regularity of P3HT is observed.     

Study of the effect of non-planarity and defects on the geometrical accuracy of semiconductor surface structures using a CA_TCAD system

As the integrated circuits (ICs) are pushed deeper into the submicrometer region, the presence of non-planarity and defects are becoming major yield detractors. In this work, we have studied these effects using a two-dimensional technology computer-aided design (TCAD) system based on cellular automata (CAs), which we have named CA_TCAD. It comprises a photolithography etching and a deposition simulator. The photolithography etching simulator has been tested, verified, and calibrated with a series of experiments with periodic and isolated lines on negative resist-coated Si wafers, using a stepper and a deep UV source at 248 nm. The deposition simulator can provide scanning electron microscopy (SEM)-like cross-sectional views, and the simulated profiles obtained are in very good agreement with experimental results found in the literature.     

Electromagnetic instability of surface waves in semiconductor superlattices

It is shown that in semiconductor superlattices surface electromagnetic waves traveling in the direction parallel to the external static electric field may become unstable. This instability manifests itself in the emission of electromagnetic waves. The instability criteria are derived, and the frequency as well as the growth increment and the direction of the emitted waves are determined.     

Modelling nonlocal processes in semiconductor devices with exponential difference schemes

In this paper nonlocal quasi-hydrodynamic mathematical models describing non-equilibrium physical processes in semiconductor devices are considered. These processes cannot be adequately described with conventional drift-diffusion models. The primary numerical difficulty arises in the energy balance equation. Details of the discretisation for the continuity equations will be described along with a transformation of the energy balance equations to give computationally convenient forms. Effective exponential difference schemes are constructed and applied to modelling transport phenomena in semiconductors. Stability conditions, computational convergence and algorithmic realisations of the proposed schemes are discussed and numerical examples are given.     

Fuzzy-based risk priority number in FMEA for semiconductor wafer processes

Semiconductor wafer manufacturing processes are considered to be complex and require considerable manpower and financial investment. Effective control to promote wafer yield is thus a very important issue. Many computational problems in traditional failure mode approaches, such as variable selection and data collection, are far too dependent on the experience of engineers, with a lack of specifically quantified values. Therefore, there are significant differences between the results of research and the actual processes. Although several researchers have revised the failure mode computation, the occurrence results continue to differ from the actual quantified values. The potential failure mode in semiconductor wafer manufacturing processes is effectively discussed using linguistic fuzzy variables to replace the severity and detection in the failure mode for re-calculation and sorting, along with the occurrence acquired from the wafer processes yield change. Based on the results of engineering experiments, the use of a risk priority number can effectively overcome the problem of a lack of objectivity in the traditional failure mode and effect analysis, as well as accurately distinguish the priority of the key failure factors so that the research results become more complete.     

Nanochemistry at the atomic scale revealed in hydrogen-induced semiconductor surface metallization

Passivation of semiconductor surfaces against chemical attack can be achieved by terminating the surface-dangling bonds with a monovalent atom such as hydrogen. Such passivation invariably leads to the removal of all surface states in the bandgap, and thus to the termination of non-metallic surfaces. Here we report the first observation of semiconductor surface metallization induced by atomic hydrogen. This result, established by using photo-electron and photo-absorption spectroscopies and scanning tunnelling techniques, is achieved on a Si-terminated cubic silicon carbide (SiC) surface. It results from competition between hydrogen termination of surface-dangling bonds and hydrogen-generated steric hindrance below the surface. Understanding the ingredient for hydrogen-stabilized metallization directly impacts the ability to eliminate electronic defects at semiconductor interfaces critical for microelectronics, provides a means to develop electrical contacts on high-bandgap chemically passive materials, particularly for interfacing with biological systems, and gives control of surfaces for lubrication, for example of nanomechanical devices.     

Plasma-assisted chemical vapor deposition processes and their semiconductor applications

When plasmas are used to assist chemical vapor deposition processes little thought is given to the nature of the electrical discharge that creates the plasma or the interaction between the plasma and the chamber. In this paper, some of the phenomena essential to the understanding of plasma behavior are reviewed. At the same time, some new reactor concepts that may offer improvements over traditional production reactors will be discussed.     

Molecular deformation processes in gel-spun polyethylene fibres

The structure/property relationships in the PE fibres have been interpreted quantitatively using a microfibrillar model and the low-strain mechanical properties have been analysed using the Takayanagi models. Information obtained from Raman spectroscopy in the previous paper has been analysed to determine the molecular deformation behaviour of the gel-spun polyethylene (PE) fibres. It is demonstrated that there is a bimodal distribution of stress in the crystalline regions due to the two-phase microstructure of the fibres and it has been shown that the molecular deformation behaviour can be interpreted quantitatively using a parallel-series model. It is found that the Young's modulus of the crystalline regions increases with the degree of chain extension and for the highest-modulus fibres may be close to the theoretical modulus of polyethylene. The fibre modulus is reduced by the presence of low-modulus non-crystalline material in parallel with the crystals.     

The influence of surface oxide on the growth of metal/semiconductor nanowires

We report the critical effects of oxide on the growth of nanostructures through silicide formation. Under an in situ ultrahigh vacuum transmission electron microscope, it is observed from the conversion of Si nanowires into the metallic PtSi grains epitaxially through controlled reactions between lithographically defined Pt pads and Si nanowires. With oxide, instead of contact area, single crystal PtSi grains start forming either near the center between two adjacent pads or from the ends of Si nanowires, resulting in the heterostructure formation of Si/PtSi/Si. Without oxide, transformation from Si into PtSi begins at the contact area between them, resulting in the heterostructure formation of PtSi/Si/PtSi. The nanowire heterostructures have an atomically sharp interface with epitaxial relationships of Si(20-2)//PtSi(10-1) and Si[111]//PtSi[111]. Additionally, it has been observed that the existence of oxide significantly affects not only the growth position but also the growth behavior and the growth rate by two orders of magnitude. Molecular dynamics simulations have been performed to support our experimental results and the proposed growth mechanisms. In addition to fundamental science, the significance of the study matters for future processing techniques in nanotechnology and related applications as well.     

Dynamically modulating the surface plasmon resonance of doped semiconductor nanocrystals

Localized surface plasmon absorption features arise at high doping levels in semiconductor nanocrystals, appearing in the near-infrared range. Here we show that the surface plasmons of tin-doped indium oxide nanocrystal films can be dynamically and reversibly tuned by postsynthetic electrochemical modulation of the electron concentration. Without ion intercalation and the associated material degradation, we induce a > 1200 nm shift in the plasmon wavelength and a factor of nearly three change in the carrier density.     

The influence of photoelectron processes in a semiconductor substrate on the adsorption of polycationic and polyanionic molecules

White-light illumination during the adsorption of polyanionic molecules of glucose oxidase (GO _x ) enzyme on the surface of p-Si/SiO₂/polyethylenimine structure leads to a threefold decrease in the surface concentration of GO _x molecules. Same illumination during the GO _x adsorption on the n-Si/SiO₂/PEI structure leads to a sevenfold increase in the surface concentration of enzyme molecules. Changes in the amount of adsorbed GO _x molecules depending on the intensity of irradiation are explained by electron transfer processes and recharging of electronic states at the Si/SiO₂ interface and within SiO₂ layer.