Ultrafast carrier dynamics in ferromagnetic InGaMnAs

We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period 20 ps, which we interpret as coherent acoustic phonons.     

Charge manipulation and imaging of the Mn acceptor state in GaAs by cross-sectional scanning tunneling microscopy

An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn²⁺3d⁵+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state.     

A Nonlinear Drift - Diffusion System with Electric Convection Arising in Electrophoretic and Semiconductor Modeling

A multi-dimensional transient drift-diffusion model for (at most) three charged particles, consisting of the continuity equations for the concentrations of the species and the Poisson equation for the electric potential, is considered. The diffusion terms depend on the concentrations. Such a system arises in electrophoretic modeling of three species (neutrally, positively and negatively charged) and in semiconductor theory for two species (positively charged holes and negatively charged electrons). Diffusion terms of degenerate type are also possible in semiconductor modeling. For the initial boundary value problem with mixed Dirichlet - Neumann boundary conditions and general reaction rates, a global existence result is proved. Uniqueness of solutions follows in the Dirichlet boundary case if the diffusion terms are uniformly parabolic or if the initial and boundary densities are strictly positive. Finally, we prove that solutions exist which are positive uniformly in time and globally bounded if the reaction rates satisfy appropriate growth conditions.     

Organometallic chemistry related to applications for microelectronics in Japan

This is meant to be a brief overview of the developments of research activities in Japan on organometallic compounds related to their use in electronic and optoelectronic devices. The importance of organometallic compounds in the deposition of metal and semiconductor films for the fabrication of many electronic and opto-electronic devices cannot be exaggerated. Their scope has now extended to thin-film electronic ceramics and high-temperature oxide superconductors. A variety of organometallic compounds have been used as source materials in many types of processing procedures, such as metal–organic chemical vapor deposition (MOCVD), metalorganic vapor-phase epitaxy (MOVPE), metal–organic molecular-beam epitaxy (MOMBE), etc. Deposited materials include silicon, Group III–V and II–VI compound semiconductors, metals, superconducting oxides and other inorganic materials. Organometallic compounds are utilized as such in many electronic and optoelectronic devices; examples are conducting and semiconducting materials, photovoltaic, photochromic, electrochromic and nonlinear optical materials. This review consists of two parts: (I) research related to the fabrication of semiconductor, metal and inorganic materials; and (II) research related to the direct use of organometallic materials and basic fundamental research.     

Frequency domain measurements on Na2B4O7−V2O5 semiconducting glass

Summary Dielectric measurements on Na₂B₄O₇(99.5%)−V₂O₅(0.5%) glass system, in the frequency range 10⁻³ to 10⁴ Hz and temperature range 300 to 500 K, have been carried out. The normalized plots of complex capacitance have shown a single mechanism responsible for conduction for both volume and surface measurements with their close values of activation energies (0.67±0.03) eV and (0.64±0.03) eV, respectively. The low-frequency dispersion (LFD) behaviour has been observed to be perturbed by the presence of more than one competing process. The impedance plots have shown a parallel combination of a capacitor (C) and a resistor (R), with some contribution of a dispersive element due to charge accumulation in the vicinity of the electrodes. The values ofR andC were found to be of the same order of magnitude, for both surface and volume measurements. The observedR has shown a decrease with an increase in temperature due to an increase in mobility of Na⁺ ions, whereasC remains practicaly constant. The complex capacitance surface behaviour is dominated by volume, due to hygroscopy of this glass system.     

一类退化半导体方程弱解存在性的研究

文章研究了当■(s)=sm(m>1),b(s)=s2和初值为u0,v0∈L 2(Ω)时一类退化半导体方程弱解的存在性．文章首先将原问题正则化,然后对正则化问题在L 2(Ω)空间上做出了有界估计,最后利用收敛性得到了问题的结论．     

The electronic structure of the interface between thin conjugated oligomer films and inorganic substrates with different work function

In this work, a comparison of the interfacial electronic properties between a semiconducting oligomer and a variety of substrates with different properties—metal, semiconductor and oxide layers—is reported. The interface formation was studied by X-ray and Ultraviolet photoelectron spectroscopies (XPS, UPS). High purity oligomer films with thickness up to 10 nm were prepared by stepwise evaporation on the clean substrates under ultrahigh vacuum (UHV) conditions. Analysis of the oligomer and substrate related XPS spectra clarified the interfacial chemistry and band bending in the semiconducting materials. The valence band structure and the interfacial dipoles were determined by UPS. The barriers for hole injection were measured at the interfaces of the organic film with all substrates. The interfacial energy band diagrams were deduced in all cases from the combination of XPS and UPS results. Emphasis was given on the influence of the substrate work function (eΦ) on the electronic properties of these interfaces.     

Ion synthesis and laser annealing of Cu nanoparticles in Al2O3

Al₂O₃ samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×10¹⁷ ion/cm² and a current density from 2.5 to 12.5 μA/cm², were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm². The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more likely to be reduced in size than to undergo oxidation. Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002     

WLY100型顺序扫描ICP光谱仪设计方案的一些考虑

本文对国产ＷＬＹ１００型顺序扫描ＩＣＰ光谱仪在设计中对单色仪，高频发生器，扫描机构，测光系统，短紫外光域的测量，恒温，气流控制与软件编制等方案的选择作了详尽的阐述，稳妥的方案使研制工作顺利进行，保证整机一次成功。