Optical Properties Of Dislocations Research Articles

Mapping the conducting channels formed along extended defects in SrTiO3 by means of scanning near-field optical microscopy

Mixed ionic-electronic-conducting perovskites such as SrTiO3 are promising materials to be employed in efficient energy conversion or information processing. These materials exhibit a self-doping effect related to the formation of oxygen vacancies and electronic charge carriers upon reduction. It has been found that dislocations play a prominent role in this self-doping process, serving as easy reduction sites, which result in the formation of conducting filaments along the dislocations. While this effect has been investigated in detail with theoretical calculations and direct observations using local-conductivity atomic force microscopy, the present work highlights the optical properties of dislocations in SrTiO3 single crystals. Using the change in optical absorption upon reduction as an indicator, two well-defined arrangements of dislocations, namely a bicrystal boundary and a slip band induced by mechanical deformation, are investigated by means of scanning near-field optical microscopy. In both cases, the regions with enhanced dislocation density can be clearly identified as regions with higher optical absorption. Assisted by ab initio calculations, confirming that the agglomeration of oxygen vacancies significantly change the local dielectric constants of the material, the results provide direct evidence that reduced dislocations can be classified as alien matter embedded in the SrTiO3 matrix.

Line defects in crystals and flux pinning in superconductors Scientific work of Reiner Labusch (1935 – 2016)

Reiner Labusch, one of the co-founders of the Conference on Extended Defects in Semiconductors in 1978, and his group made seminal contributions to a fundamental understanding of the electrical and optical properties of dislocations in semiconductors, the fluxon pinning in Type II superconductors, and the solid solution hardening of alloys.With regard to semiconductors, he developed occupation statistics and a band scheme for optical transitions of a half-filled band arising from dangling bonds in the dislocation core that could explain the carrier density in plastically deformed p- as well as n-type germanium and devised experimental setups for photoconductivity measurements avoiding the blurring effect of surface states in Ge and Si and measurements on bundles of single dislocations in CdS and Ge. He extended the band model by introducing empty bands split from the conduction band in the strain field of dislocations. This model is most convincingly confirmed for 90° partial dislocations in Ge by photoconductivity spectra on individual dislocations.Reiner Labusch's theoretical studies on superconductivity include (i) the elastic properties of the fluxoid lattice in type II superconductors, (ii) the nature and properties of fluxoid lattice dislocations and (iii) a rigorous statistical theoretical treatment of the response or, in particular the “pinning”, of the fluxoid lattice to pinning sites/defects in the crystal lattice, and (iv) on the magnetization behavior in type II superconductors of arbitrary shape. This latter rigorous analysis and numerical treatment allowed for the accurate prediction, and a contribution to the understanding of the magnetization properties in disc/platelet samples, including inter alia, the initial fluxoid penetration behavior, fluxoid pinning, and fluxoid lattice transformations relating to the “arrow-head” phenomenon, fluxoid lattice melting and the “intermediate state”.Labusch’s statistical theory of solid solution hardening is based on a fundamental understanding of the interaction of a dislocation moving through a random array of solute atoms or precipitated particles. It yielded an expression for the critical resolved shear stress as a function of the obstacle concentration, the interaction force and range of interaction between the dislocation and a single obstacle, and the dislocation line tension. The analytical result was corroborated by computer simulations which also revealed that the strengthening by extended obstacles in most alloys is beyond the ‘Friedel-limit’ and is adequately described by the ‘Labusch theory’.

Electronic and Optical Properties of Dislocations in Silicon

Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase of the drain current of metal-oxide-semiconductor field-effect transistors (MOSFETs) if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10% or more—causes locally dramatic changes of the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas and single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

Properties of Interfacial Dislocations in Hydrophobic Bonded Si-Wafers

The realization of defined dislocation networks by hydrophobic wafer bonding allows the characterization of electrical and optical properties of dislocations. The present paper investigates the electrical properties in samples containing only a few (up to 6) dislocations. By taking results of other analysis into account the electronic properties of individual dislocations can be described. The dislocation-induced luminescence between 1.3 µm and 1.5 µm was also analyzed using different types of light-emitting diodes (LED). It was shown that the emission depends on the structure of the dislocation network.

Correlation of electrical and luminescence properties of a dislocation network with its microscopic structure

AbstractThe direct bonding of Si wafers reproducibly forms dislocation networks (DN) with a microscopic structure defined by the mutual crystallographic orientation between the pair of wafers used for the bonding procedure. This allows studying the electrical and optical properties of specific dislocations. In the present work three different DN structures were investigated using transmission electron microscopy (TEM), photoluminescence (PL) and deep level transient spectroscopy (DLTS). The results show close correlation between the structural, electrical and optical properties of dislocations and opens a possibility to identify structural peculiarities of the dislocations responsible for the high intensity of photoluminescence. Namely, the obtained results suggest that PL at ∼0.8 eV is related to screw dislocations in DN. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dislocations as Active Components in Novel Silicon Devices

AbstractThe electrical and optical properties of dislocations in Si are reviewed, namely dislocation‐related recombination and luminescence, transport of minority and majority carriers along dislocations or the electric field around dislocations. It is shown that Si wafer direct bonding allows well‐controlled formation of dislocation networks, giving rise to adjustable dislocation properties. Ideas for novel Si devices utilizing dislocations as active components are presented. In particular, dislocation‐based light emitters at about 1.5 µm wavelength are demonstrated. Concepts for dislocation‐based conductive channels and fast FETs, manipulators of biomolecules or thermo‐electric generators are sketched.

Optical properties of dislocations in wurtzite ZnO single crystals introduced at elevated temperatures

Optical properties of wurtzite ZnO bulk single crystals in which an arbitrary number (typically 109–1010 cm−2) of fresh dislocations were introduced intentionally by the plastic deformation at elevated temperatures (923–1073 K) were examined. Deformed specimens showed excitonic light emission with photon energies of 3.100 and 3.345 eV, as well as their LO phonon replicas at 11 K. The light intensities increased with increasing dislocation density. The activation energy for a thermal quenching of the 3.100 or 3.345 eV emission band, which corresponds to the depth of the localized energy level associated with the emission band, was estimated to be 0.3±0.1 or 0.05±0.01 eV, respectively. The origin of the energy levels was proposed as point defect complexes involving dislocations. The introduction of the dislocations at the elevated temperatures above 923 K did not influence the intensities of the emission bands except the dislocation-related emission bands.

Electrical and Optical Properties of Dislocations Generated under Pure Conditions

Electrical and Optical Properties of Dislocations Generated under Pure Conditions

Dislocation luminescence in nitrogen-doped Czochralski and float zonesilicon

This paper reports the results of a study of the effect of nitrogen on the opticalproperties of dislocations in nitrogen-doped Czochralski and nitrogen-doped floatzone silicon samples where the nitrogen doping was carried out by adding Si3N4in the molten silicon charge or by nitrogen gas dissolution. Dislocations wereintroduced by plastic deformation at 650°C. In nitrogen-doped plasticallydeformed samples, emissions in the range of the D1–D4 bands of dislocations arepresent with a significant shifting from the energies and intensities of thecorresponding bands in nitrogen-free samples. It has been shown that the maineffect of nitrogen could be the enhancement of the oxygen precipitation. Theresults confirm the suggestion of some of the present authors that luminescence at0.830 eV is associated with some intrinsic properties of oxygen precipitates.

Oxygen Effect on Electrical and Optical Properties of Dislocations in Silicon

The DLTS (Deep Level Transient Spectroscopy) and PL (Photoluminescence) spectra of dislocations introduced in Cz-Si (single crystal grown by the Czochralski method) under clean conditions have been studied. The oxygen effect on the formation of both spectra has been revealed. For the first time, a concomitant decay of both PL and DLTS signals with deformation duration in the range of 0.25 to 14 h was observed. Preliminary results show that one of the important parameters responsible for the electrical and optical properties of the dislocations could be the distance covered by the dislocations.

Effect of oxygen aggregation processes on the recombining activity of 60° dislocations in Czochralski grown silicon

The interaction of dislocations with light elements like oxygen and carbon presents a variety of aspects which are of basic interest for the understanding of gettering processes, as well as for a deeper knowledge of the electrical and optical properties of dislocations. We report the results of a systematic investigation of the influence of the dislocations on the segregation of oxygen and of the effect of oxygen segregation on their electrical activities. The experiments were carried out on p-type Czochralski silicon, in the 700–1100 °C temperature range. It has been shown that not only a direct oxygen-dislocation interaction occurs, but also that a competition between homogeneous and heterogeneous segregation processes occurs, which influences the overall electrical properties of the samples as well.

Electronic transport and optical properties of dislocations in deformed compound semiconductors

Electronic transport and optical properties of dislocations in deformed compound semiconductors