高离化态金离子的辐射复合及其退激发过程的理论研究

利用基于多组态Dirac-Fock方法的程序包GRASP92和RATIP以及最新发展的RERR06程序,详细计算了高离化态金离子(类镍Au51+、类铜Au50+和类锌Au49+)俘获一个自由电子到nl(n=4—8,l=0—3)壳层的辐射复合谱以及相应的辐射退激发谱.理论计算的辐射复合谱很好地重现了实验谱.研究结果表明:对类镍Au51+、类铜Au50+和类锌Au49+而言,将一个自由电子俘获到n=4壳层的概率最大;在辐射复合过程之后,处在n=4壳层的俘获电子的辐射退激发谱线最强,并且体现了整个辐射退激发谱的主要特征.     

Homogenized Lorentz-Drude optical response in highly nanoporous conducting gold layers produced by de-alloying

Nanoporous gold films produced by de-alloying AuAl₂ with void densities between 45% and 65% retain high infra-red reflectance and good conductivity. They act optically like a homogeneous Lorentz-Drude metal with a unique plasma frequency and an inter-band transition energy unchanged from that of dense gold. The link between and ω_p in dense gold is found using a simplification of the Bergman expansion for permittivity valid at infra-red wavelengths. The carrier relaxation time of the “effective metal” becomes the actual relaxation time in the Au network and the complex refractive indices (n, k) found using normal incidence spectrophotometry and oblique incidence ellipsometry agree closely with each other. The single pole approximation for the ratio in the infra-red allows estimates of void content and the apparent shift in carrier effective mass. It is then possible to model with no adjustable parameters, the full UV-visible-NIR spectral response, giving excellent agreement with data. A range of films with these properties are presented.     

Hopping conduction in epitaxial n-GaAs layers

The conductivity results of the phonon-assisted hopping process in n-type GaAs at low temperatures are presented. The conductivity variation with T, N_D and H are analyzed in terms of the percolation theory results.     

Effect of surface defects on radiative interband recombination in silicon nanocrystals highly doped with hydrogen-like impurities

The role of surface defects at the Si nanocrystal boundary during the process of interband radiative recombination is studied in the case in which nanocrystals are doped with hydrogen-like impurities with shallow energy levels. It is shown that, in the case of a nonpassivated surface with a large number of dangling bonds, the rate of radiative transitions in nanocrystals doped with donors can be larger than that in nondoped crystallites. On the other hand, doping with acceptors leads to a decrease in the rate of transitions. In the case of a completely passivated surface, the recombination rate remains almost unchanged irrespective of the type of dope.     

Calculation of photon angular distribution and polarization for radiative recombination for highly charged helium-like ions

A systematic study is carried out on the angular distribution and polarization of photons emitted following radiative recombination of He-like ions by a non-relativistic dipole approximation. In order to incorporate the screening effect due to inner-shell electrons, a distorted wave approach is used. The dependence of the calculated angular distribution and polarization on the reduced-energy and nuclear charge are fitted by the corresponding empirical formulas, respectively.     

X-ray diffractometric study of the influence of a buffer layer on the microstructure of molecular-beam epitaxial InN layers of different thicknesses

Thin layers of InN are grown by molecular beam epitaxy on (0001) sapphire substrates. The influence of thin (15 nm) InN buffer layers and their temperature treatment on the structural quality of the grown layers is investigated by double-crystal and triple-crystal x-ray diffractometry. It is revealed that the preliminary high-temperature (900°C) annealing of the buffer layer leads to a notable improvement in the quality of the layers grown on this buffer. The densities of vertical screw and vertical edge dislocations decrease (to 1.9×10⁸ cm⁻² and 1.3×10¹¹ cm⁻², respectively) with an increase in the distance from the interface (by ∼1 μm). __________ Translated from Fizika Tverdogo Tela, Vol. 43, No. 5, 2001, pp. 913–917. Original Russian Text Copyright ? 2001 by Ratnikov, Mamutin, Vekshin, Ivanov.     

Suppression of intermixing in strain-relaxed epitaxial layers

Misfit strain plays a crucial role in semiconductor heteroepitaxy, driving alloy intermixing or the introduction of dislocations. Here we predict a strong coupling between these two modes of strain relaxation, with unexpected consequences. Specifically, strain relaxation by dislocations can suppress intermixing between the heterolayer and the substrate. Monte Carlo simulations and continuum modeling show that the suppression, though not absolute, can be surprisingly large, even at high temperatures. The effect is strongest for a large misfit (e.g., InAs on GaAs) or for thin substrates (e.g., Ge on silicon on insulator).     

Interdiffusion of layers in PbSe-PbS epitaxial superlattices

X-ray diffraction methods are used to investigate the diffusional mixing of layers in PbSe-PbS superlattices. The interdiffusion coefficients of the layers are determined from the change in the intensity of satellite reflections. Two stages of diffusion are observed — fast (at the initial stages of anneals) and slow. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 9, 685–687 (10 November 1998)     

Photoconductive response of GaAs epitaxial layers

In the present work the photoconductive response of low resistivity, n-type GaAs epitaxial layers is studied by experimentally monitoring the dependence of the photoconductive gain (PG) optoelectronic parameter upon incident photon flux and temperature. The characterized samples fall into three major categories: ion implanted (II) GaAs epilayers formed within undoped, semi-insulating GaAs substrates; GaAs epitaxial layers grown by liquid phase epitaxy (LPE) on Cr-doped, semi-insulating GaAs substrates; and ungated GaAs MESFETs.     

Ohmic contacts to GaAs epitaxial layers

Formation of ohmic contacts onto GaAs epitaxial layers was reviewed. Because the Fermi energy of GaAs is pinned at the surface near the middle of the bandgap, it is impossible to choose a metal with the proper work function to make an ohmic contact. Instead, it is necessary to create a heavily doped surface layer and using field emission or thermionic field emission to achieve an ohmic contact. The oldest known contact metallization for GaAs is sequentially deposited thin films of Au, Ge, and Ni. It was shown that the ‘dopant diffusion model’, widely accepted to date to explain the formation of an n⁺ layer on GaAs to form the ohmic contact, is incorrect. Instead, the “solid phase regrowth model” was discussed in detail and shown to describe formation of ohmic contacts in this system. Based on this result, general rules for forming ohmic contacts to compound semiconductors with pinned Fermi levels or large values of electron affinities plus bandgap were expressed.     

Growth of InN layers by MOVPE using different substrates

This study presents the MOVPE growth of InN films onto different substrate materials, including sapphire, nitrided or not, GaN and AlN buffer layers deposited onto sapphire, and Si(111).For InN growth onto nitrided sapphire, different growth parameters were investigated in order to determine the best growth conditions. We found that a low V/III molar ratio has to be used in order to increase the growth rate. A light nitridation treatment gives the best electrical properties: mirror like layers with a mobility of 800 cm²/V  s were obtained. At room temperature, reflectivity experiments show the existence of a transition at 1.2 eV, while photoluminescence appears around 0.8 eV.Using the same growth conditions onto GaN buffers (with thicknesses ranging from 15 to 1000 Å), we found that the best mobilities are obtained above a given buffer thickness.By comparing also with AlN buffer layers and silicon substrates, we found that our previous conclusion still holds; lightly nitrided sapphire substrate leads to the best electrical properties and morphology.