O.F. Vyvenko

Exponential analysis in physical phenomena

Many physical phenomena are described by first-order differential equations whose solution is an exponential decay. Determining the time constants and amplitudes of exponential decays from the experimental data is a common task in semiconductor physics (deep level transient spectroscopy), biophysics (fluorescence decay analysis), nuclear physics and chemistry (radioactive decays, nuclear magnetic resonance), chemistry and electrochemistry (reaction kinetics) and medical imaging. This review article discusses the fundamental mathematical limitations of exponential analysis, outlines the critical aspects of acquisition of exponential transients for subsequent analysis, and gives a comprehensive overview of numerical algorithms used in exponential analysis. In the first part of the article the resolution of exponential analysis as a function of noise in input decays is discussed. It is shown that two exponential decays can be resolved in a transient only if the ratio of their time constants is greater than t...

X-ray beam induced current/microprobe x-ray fluorescence: synchrotron radiation based x-ray microprobe techniques for analysis of the recombination activity and chemical nature of metal impurities in silicon

In this study we report applications of the synchrotron radiation based x-ray microprobe techniques, x-ray beam induced current (XBIC) and microprobe x-ray fluorescence (μ-XRF), to the analysis of the recombination activity and spatial distribution of transition metals in silicon. A combination of these two techniques enables one to study the elemental nature of defects and impurities and their recombination activity in situ and to map metal clusters with a micron-scale resolution. The correspondence between XBIC data and the data obtained by conventional recombination-sensitive mapping techniques such as electron beam induced current and laser beam induced current is demonstrated. An approach that allows determination of the depth of metal precipitates from several XBIC/μ-XRF images taken for different sample orientations is suggested and is experimentally demonstrated.

Synthesis and structure of poly-3,4-ethylenedioxythiophene film with the inclusions of palladium nanoparticles

By chemical deposition of ultrafine particles of metallic palladium on the polymer matrix of poly-3,4-ethylenedioxythiophene (PEDOT) composite PEDOT/Pd films were obtained. The conditions of synthesis of the composite films in dependence on the duration of exposure of the reduced form of PEDOT film in a solution of palladium chloride, its concentration and the film thickness were studied. By the methods of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) it was shown that in the process of the synthesis of the composite films the nanosized palladium particles of predominantly quasispherical shape precipitated on the globular structure of the polymer. The size of the palladium nanoparticles in the composite PEDOT film and the nature of their distribution over the film bulk were revealed. An increase in the duration of deposition of the palladium nanoparticles on the film was shown to lead to an increase in their size and in the density of particles in the film.

Electrical levels of dislocation networks in p- and n-type Si

The results of deep level transient spectroscopy (DLTS) and minority carrier transient spectroscopy (MCTS) investigations on directly bonded n- and p-type silicon wafers with small twist misorientation angles ranging from 1 to 5 degrees are presented and discussed. Both shallow and deep levels in the upper half of a band gap are found and a good correspondence between the DLTS and MCTS data on n- and p-type samples was established. The dependence of DLTS-peak magnitude on twist and tilt misorientation angles (density of dislocations) was investigated and the origin of different levels is suggested.

Transport of Massless Dirac Fermions in Non-topological Type Edge States

There are two types of intrinsic surface states in solids. The first type is formed on the surface of topological insulators. Recently, transport of massless Dirac fermions in the band of “topological” states has been demonstrated. States of the second type were predicted by Tamm and Shockley long ago. They do not have a topological background and are therefore strongly dependent on the properties of the surface. We study the problem of the conductivity of Tamm-Shockley edge states through direct transport experiments. Aharonov-Bohm magneto-oscillations of resistance are found on graphene samples that contain a single nanohole. The effect is explained by the conductivity of the massless Dirac fermions in the edge states cycling around the nanohole. The results demonstrate the deep connection between topological and non-topological edge states in 2D systems of massless Dirac fermions.

Combined CL/EBIC/DLTS investigation of a regular dislocation network formed by Si wafer direct bonding

Electrical levels of the dislocation network in Si and recombination processes via these levels were studied by means of the combination of grain-boundary deep level transient spectroscopy, grain-boundary electron beam induced current (GB-EBIC) and cathodoluminescence (CL). It was found two deep level traps and one shallow trap existed at the interface of the bonded interface; these supply the recombination centers for carriers. The total recombination probability based on GB-EBIC data increased with the excitation level monotonically; however, the radiative recombination based on D1-D2 CL data exhibited a maximum at a certain excitation level. By applying an external bias across the bonded interface, the CL signal of D-lines was enhanced dramatically. These results are consistent with our models about two channels of recombination via the trap levels.

Extension of Hydrogen Passivation of Intragrain Defects and Grain Boundaries in Cast Multicrystalline Silicon

The recombination activity of crystal defects was studied along cross-sections of cleaved multicrystalline silicon wafers (Silso®) grown by block casting. The temperature dependence of the electron-beam-induced current (EBIC) contrast c(T) was analyzed to study defect passivation by remote hydrogen plasma treatment with respect to (i) the extension and (ii) the degree of passivation. Based upon model calculations, the c(T) behavior allows estimating the degree of contamination of recombination active crystal defects. After hydrogen treatment of 1 h at 310°C the number of defect-related deep levels at grain boundaries is reduced by a factor of three to four. Low-temperature EBIC reveals that hydrogenation also reduces the density of active centers at defects which exhibit already very low or no (detectable) EBIC contrast at room temperature such as intragrain defects. Both defects in intragrain regions and grain boundaries are passivated down to about 100 μm. No indications were found for significantly enhanced hydrogen diffusion along grain boundaries.

Electronic States of Oxygen-Free Dislocation Networks Produced by Direct Bonding of Silicon Wafers

The results of experimental investigations of the dislocation-related DLTS-peaks originated from the dislocation networks (DN) are presented. Samples with DNs were produced by direct bonding of p-type silicon wafers and no enhancement of oxygen concentration was detected near the DN plane. Origins of the DLTS peaks were proposed and a correlation with the dislocation-related photoluminescence data was established based on known dislocation structure of the samples. Two types of shallow DLTS peaks exhibited Pool-Frenkel effect, which could be linked to the dislocation deformation potential. One of the shallow DLTS peaks was related to straight parts of screw dislocations and another - to the intersections of the dislocations.

Regular Dislocation Networks in Silicon as a Tool for Novel Device Application

The paper deals with possibilities of utilizing dislocation structures as active components of devices. The suggested means for controlled formation of dislocations is direct wafer bonding, giving rise to well defined dislocation networks with adjustable properties. It is shown that the networks allow building light emitting diodes based on the D line luminescence of the dislocations. A light emitter at about 1.5 mm wavelength is demonstrated, with an efficiency potential estimated at 1%. Immobilization of biomolecules on Si surfaces by Coulomb interaction with the dislocations in the network is another application discussed. Finally, the potential use of dislocation networks as insulating layers permeable to impurities to be gettered and as three-dimensional buried conductive channels in the Si wafer is addressed.

Recombination activity and electrical levels of dislocations in p-type Si∕SiGe structures: Impact of copper contamination and hydrogenation

The impact of copper contamination and subsequent hydrogenation on recombination activity and hole-trap levels of misfit dislocations were investigated in p-type Si∕Si0.98Ge0.02∕Si structures. In the as-grown (noncontaminated) samples, dislocations were found to exhibit very low recombination activity, detectable with the electron-beam-induced current technique only at low temperatures. Deep-level transient spectroscopy revealed a dislocation-related hole-trap level at Et=Ev+0.2eV. The position of the observed level is close to the theoretically predicted hole-trap state of the intrinsic stacking fault of a dissociated dislocation. Contamination with a low copper concentration [5 (parts per 109) ppb] gave rise to a large increase of the recombination activity of the dislocations and to the appearance of another dislocation-related defect level at Et=Ev+0.32eV. Hydrogenation of the samples by a treatment with an acid solution and subsequent reverse-bias anneal at 380K resulted in the evolution of the level...