The use of channeling-effect techniques to locate interstitial foreign atoms in silicon

When the channeling-effect technique is used to determine the lattice location of an impurity which is not completely substitutional, quantitative interpretation of the results requires knowledge of the interaction yield between a channeled beam and an interstitial atom. We have investigated this problem for Yb implanted into silicon. Along the <110> direction, a peak of almost a factor of two is observed in backscattering yield from the Yb atoms, using a 1-MeV He beam. The height and angular width of the peak is satisfactorily interpreted in terms of flux-peaking of the channeled beam in the central region of the <110> channels.

The existence of such a large flux-peaking effect seriously complicates quantitative determination of the location of non-substitutional impurities. However, it is still possible to establish rather accurately the lattice position of the impurity, provided the measured minimum yields and angular widths of the <111> and <100> dips are taken into account.     

Mössbauer study of 57Fe in GaAs and GaP following 57Mn+ implantation

Ion implantation provides a precise method of incorporating dopant atoms in semiconductors, provided lattice damage due to the implantation process can be annealed and the dopant atoms located on regular lattice sites. We have undertaken ⁵⁷Fe emission Mössbauer spectroscopy measurements on GaAs and GaP single crystals following implantation of radioactive ⁵⁷Mn^?+? ions, to study the lattice sites of the implanted ions, the annealing of implantation induced damage and impurity–vacancy complexes formed. The Mössbauer spectra were analyzed with four spectral components: an asymmetric doublet (D1) attributed to Fe atoms in distorted environments due to implantation damage, two single lines, S1 assigned to Fe on substitutional Ga sites, and S2 to Fe on interstitial sites, and a low intensity symmetric doublet (D2) assigned to impurity–vacancy complexes. The variations in the extracted hyperfine parameters of D1 for both materials at high temperatures (T?> 400 K) suggests changes in the immediate environment of the Fe impurity atoms and different bonding mechanism to the Mössbauer probe atom. The results show that the annealing of the radiation induced damage is more prominent in GaAs compared to GaP.     

Effect of the fermi level position in silicon on ion-induced displacement of impurities

Abstract

With the channeling technique the lattice location of both As and B is studied in single As-or B-doped and in doubly As-and B-doped silicon single crystals. The influence of the position of the Fermi-level on the displacement of impurity atoms off substitutional lattice sites is investigated by changing the crystals from n- to p?type or vice versa by choosing implant conditions and annealing termperatures for the doubly doped crystals in an appropriate way. Big changes were found in displacement cross sections for As and B after conversion of the crystals from n- to p-type. The results can be explained by assuming that the interaction between primary defects and impurity atoms causing the displacement of the impurity atom is controlled by Coulomb attraction between charged point defects and the impurity atoms.     

FIM observation of A Ga(3 × 3) superstructure on W and Mo(011)

FIM observation has revealed that the atomic arrangement of a monoatomic Ga layer on the W and Mo(011) plane is the (3 × 3) superstructure formed by zigzag chains of Ga atoms. Observed images indicate that the Ga atoms of the zigzag chains are displaced in the [01&#x0304;1] or [011&#x0304;] direction from an open W lattice site to the position where the displaced atom is stabilized by contacting three substrate W atoms.     

Transformation of radiation-induced defects responsible for theF-band of absorption in NaF crystals subjected to irradiation with light and annealing

It has been found that the F-band of optical absorption which is observed in ψ-irradiated NaF crystals consists of three overlapping bands. The band at 345 nm of width 40 nm is independent of the impurity composition of the crystals; it disappears upon exposure to radiation at 345 nm and appears again upon annealing at 460±15 K for 15 min. This band is correlatable in intensity with the superfine structure of an EPR spectrum. The width (65–110 nm) and the spectral position (355–375 nm) of the second band depend on the impurity composition of the crystal. The band of width 90–110 nm at 320–325 nm disappears upon annealing and appears after exposure to light simultaneously with the disappearance of an EPR signal. It is established that the band at 345 nm is caused by quasimolecules based on fluorine atoms, that at 355–375 nm is triggered by F-centers with a different impurity composition near the haloid vacancy, and the band at 320–325 nm owes its appearance to F-centers in a negatively charged state (F′). Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, 70 F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6, pp. 849–853, November–December, 1999.     

Cathodoluminescence of ZnS single crystals subjected to thermal annealing in vapors of the constituents

The 77°K cathodoluminescence spectra of ZnS single crystals grown from the melt and annealed in vapors of the constituents were studied in the spectral region 360 to 550 nm. The single crystals contained oxygen whose phase state could be changed by thermal annealing. The effect of oxygen in the ZnS lattice on the appearance and intensities of various bands in the zinc sulfide spectrum was investigated. It turned out that the bands at 390–400 nm, 410–430 nm, and 500–525 nm are associated with the luminescence of a solid solution of ZnS· O in the lattice. The intensity of the green luminescence was a function of oxygen concentration in precipitates of the solid solution on dislocations. The luminescence in the 363 to 370 nm region is associated with zinc oxide which separates from ZnS containing various amounts of sulfur.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 84–88, May, 1975.     

注入Ar+的蓝宝石晶体退火前后光致发光谱的分析

对注入Ar⁺后不同晶面取向的蓝宝石晶体在不同退火条件下的光致发光谱进行了分析.分析结果表明:三种晶面取向的蓝宝石样品经Ar⁺注入后,其光致发光谱中均出现了新的位于506nm处的发光峰;真空和空气气氛下的退火均对样品在506nm处的发光有增强作用,不同晶面取向的样品发光增强程度不同,且发光增强至最大时的退火温度也不同,空气气氛下的退火使样品发光增强程度更为显著.由此可以看出,退火气氛、退火温度和晶面取向均对样品发光峰强度有影响. 关键词： 2O₃')" href="#">Al₂O₃ 离子注入 退火 光致发光谱     

Hyperfine field and effect of magnetic dipolar field of Fe−Si single crystal by Mössbauer spectroscopy

A Fe−Si (6at%) single crystal with a (110) surface was studied by a Mossbauer spectroscopy as a function of the angle between a crystal axis <100> and the magnetization direction <hk1>. The difference spectra reveal Si atoms give rise to a magnetic dipolar field, of which magnitude varies with the angle as expected for the Si atom in the 2nd neighbor site. The dipolar field was found to take place at the main lines of Mossbauer spectrum to reveal the Si atom in the 2nd neighbor site never reduces the hyperfine field at the Fe probe nuclei, which supports the earlier proposals by Cranshaw.     

A study on the self-interstitial structure of radiation damaged silicon by means of the double alignment channeling technique

The angular distribution of 2.8 MeV helium ions backscattered from silicon crystals containing self-interstitials has been calculated by channeling computer simulations for a double alignment channeling configuration. The structures of the self-interstitial defects are assumed to be the split <110> interstitial and the split <100> di-interstitial with various inter-atomic distances. The obtained profiles of the backscattering yield are found to show shapes characteristic for each structure which can be used for differentiating between these structures. When comparing these profiles with experimental profiles obtained with the same double alignment channeling configuration in a previous study one finds reasonable agreement for the split <110> interstitial defect with an inter-atomic distance of 1.76 Å.     

Lattice site location and electronic structure of Te in GaAs

High purity <100> wafers of GaAs were implanted with radioactive^129mTe and stable¹²⁸Te at 110 keV to total doses of 2×10¹⁴ and 2×10¹⁵ Te/cm² respectively and studied with RBS/ channeling and Mössbauer spectroscopy on the 27.8 keV level of¹²⁹I. After implantation and/or annealing at temperatures between 200–300°C the Mössbauer spectra are dominated by a single line. Channeling reveals an appreciable residual damage in the host lattice, but also points to a substitutional position of the Te atoms. After annealing above ≌500°C, where nearly complete lattice damage recovery is obtained, the Te atoms become defect-associated. The results clearly point to the formation of Te_As?V_Ga complexes.     

Enhanced photoluminescence of Ar implanted sapphire before and after annealing

In this paper, we studied the changes in the photoluminescence spectra of the Ar⁺ ion implanted mono-crystalline sapphire annealed at different atmospheres and different temperatures. Single crystals of sapphire (Al₂O₃) with the (1 0 1¯ 0) (m-samples) orientation were implanted at 623 K with 110 keV Ar⁺ ions to a fluence of 9.5×10¹⁶ ions/cm². Photoluminescence measurement of the as-implanted sample shows a new emission band at 506 nm, which is attributed to the production of interstitial Al atoms. The intensity of emission band at 506 nm first increased then decreased with increase in annealing temperature. For the same annealing temperature, the intensity of PL peak at 506 nm of the sample annealed in air was higher than the sample annealed in vacuum. The experimental results show that the intensity of the PL peak at 506 nm of Ar-implanted sapphire can be enhanced by subsequent annealing with an enhancement of nearly 20 times. The influence of thermal annealing of the Ar-implanted samples on the new 506 nm emission band was discussed.     

Influence of low and high temperature annealing on the blue and green emission bands of ZnS crystals

After annealing at 350 °C, in the luminescence spectra of pure and Cu-doped ZnS crystals a reversible blue-green conversion has been obtained. The blue-green conversion of luminescence is correlated with analogous reversible variations in the optical transmission and thermoluminescence properties. Besides these low temperature results, in the fluorescence spectra of undoped ZnS crystals, which are annealed at 1,000 °C in sealed evacuated quartz ampoules, a reversible blue-blue conversion has been observed. All these effects, induced by distinct heat treatments, seem to be mainly controlled by changes in the structural disorder or/and by the evaporation of lattice atoms from the surface of the crystals.     

Lattice location of dopant atoms: An <Emphasis Type="Italic">N</Emphasis>-body model calculation

The channelling and scattering yields of 1 MeV α-particles in the 〈100〉, 〈110〉 and 〈111〉 directions of silicon implanted with bismuth and ytterbium have been simulated using N-body model. The close encounter yield from dopant atoms in silicon is determined from the flux density, using the Bontemps and Fontenille method. All previous works reported in literature so far have been done with computer programmes using a statistical analytical expression or by a binary collision model or a continuum model. These results at the best gave only the transverse displacement of the lattice site from the concerned channelling direction. Here we applied the superior N-body model to study the yield from bismuth in silicon. The finding that bismuth atom occupies a position close to the silicon substitutional site is new. The transverse displacement of the suggested lattice site from the channelling direction is consistent with the experimental results. The above model is also applied to determine the location of ytterbium in silicon. The present values show good agreement with the experimental results.     

Growth of iron single crystals in the etched ion tracks of polymer foils

Pulse reverse electrolysis in an ultrasonic field is used to grow iron single crystals of micron size in templates formed by etching the tracks of swift ions in polymer foils. High-grade crystals are produced from high-temperature ferrous chloride baths. The crystals are oriented along their <110>, <100>, and <111> crystallographic axes. Their orientation turns out to depend on supersaturation during the growing process. At low overvoltages of deposition, <110> and <100> orientations are observed. The crystals of <111> orientation appear more frequently at higher cathode pulse current density. The crystals possess prominent resistance to corrosion. Received: 20 February 2001 / Accepted: 21 February 2001 / Published online: 3 May 2001     

Structural properties of the donor indium in nanocrystalline ZnO

The structural properties of the nanocrystalline semiconductor ZnO (nano-ZnO) doped with the donor Indium were investigated by perturbed γγ angular correlation spectroscopy (PAC) and extended X-ray absorption fine structure measurements (EXAFS). Up to an average concentration of one In atom per nanocrystallite, PAC measurements show that about 12% of the ¹¹¹In atoms are incorporated on substitutional Zn sites. At higher In concentrations, new In defect complexes are visible in the PAC spectra, which dominate the spectra if the average In concentration exceeds one In atoms per nanocrystallite. In addition, the local environment of Zn and In atoms in In doped nano-ZnO was investigated by EXAFS. The measurements at the K edge of Zn show that the crystal structure of nano-ZnO corresponds to bulk ZnO. In heavily In doped nano-ZnO the EXAFS experiments at the K edge of In exhibit an expansion of the first O shell about the In site. Since about four O atoms are detected in this first shell a substitutional incorporation of the In atoms in the ZnO lattice is suggested. The second shell to be occupied by Zn atoms as well as higher shells are almost invisible, which might have the same microscopic origin as the occurrence of defect complexes observed by PAC.     

Luminescence of CsBr:Eu films grown by liquid-phase epitaxy

By liquid-phase epitaxy from an aqueous alcoholic solution, we have obtained films of the well-known storage phospor CsBr:Eu, and we have studied their cathodoluminescence and photoluminescence (PL) spectra compared with the undoped CsBr films. We have established that the structure of the photoluminescence centers of the CsBr:Eu films when excited by laser radiation in the absorption band of the Eu²⁺ ions (λ = 337 nm) includes Eu²⁺-V_Cs isolated dipole centers and CsEuBr₃ aggregate centers, and also luminescence centers based on inclusions of hydroxyl group OH⁻ with the corresponding emission bands in the 440 nm, 520 nm, and 600 nm regions. We have studied the dependence of the spectra and the intensity of the photoluminescence for CsBr:Eu films on annealing temperature in air at 423–483 K, compared with analogous dependences for CsBr:Eu single crystals obtained from the melt. We have shown that annealing the films at T = 423–463 K leads to rapid formation of CsEuBr3 aggregate luminescence centers, while for T > 473 K thermal degradation of these centers occurs. We conclude that the observed differences between the photoluminescence spectra of CsBr:Eu films and CsBr:Eu single crystals may be due to additional doping of the films with OH⁻ ions. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 191–194, March–April, 2006.     

Directional anisotropy in the cleavage fracture of silicon

Total-energy pseudopotential calculations are used to study the cleavage anisotropy in silicon. It is shown that cracks propagate easily on 111 and 110 planes provided crack propagation proceeds in the <1;10> direction. In contrast, if the crack is driven in a <001> direction on a 110 plane the bond breaking process is discontinuous and associated with pronounced relaxations of the surrounding atoms, which results in a large lattice trapping. The different lattice trapping for different crack propagation directions can explain the experimentally observed cleavage anisotropy in silicon single crystals.     

Theoretical study of the diffusion of lithium in crystalline and amorphous silicon

The effect of the lattice deformation on potential barriers for the motion of a lithium atom in crystalline silicon has been studied through ab initio density functional calculations. A new universal method of calculating the diffusion coefficient of an admixture in amorphous solid media through the activation mechanism has been proposed on the basis of these data. The method is based on the calculation of the statistical distribution of potential barriers for the motion of an admixture atom between minima depending on the position of neighboring atoms. First, the amorphous structure, which is generated by annealing from the crystalline structure with vacancies, has been simulated. Then, the statistical distribution of the potential barriers in the amorphous structure for various local environments of the admixture atoms has been calculated by means of linear regression with the parameters determined for barriers in crystalline silicon subjected to different deformations. The diffusion coefficient of the admixture has been calculated from this distribution by using the Arrhenius formula. This method has been tested by the example of crystalline and amorphous silicon with admixture of lithium atoms. The method demonstrates that the diffusion of lithium in amorphous silicon is much faster than that in crystalline silicon; this relation is confirmed experimentally.     

LCAO studies of hydrogen chemisorption on nickel: I. Tight-binding calculations for adsorption on periodic surfaces

The model we have used to study hydrogen chemisorption on nickel surfaces is a tightbinding Extended Hückel method applied to finite (periodic) crystals up to about 250 atoms, the non-orthogonal basis set comprising five 3d orbitals, one 4s orbital and three 4p orbitals per atom. After calculating the band structure of fcc nickel, we have examined, by this model, the effect of the (100), (110) and (111) surfaces on the local density of states and the charge distribution. The results agree closely with moment calculations of the density of states in semi-infinite crystals and with experimental (XPS, UPS and INS) spectra. Extensive studies have been made of the influence of adsorption on the (partial) densities of states in order to illuminate the nature of the chemisorption bond. Particularly, we have concluded that both the 3d electrons and the conduction electrons take part in this bond. Equilibrium positions for adsorption on various sites have been determined and the adsorption energy has been computed and compared with experimental data. We find that the stability of adsorption decreases in the order (110) > (100) > (111) and Atop > Bridge > Centred.     

Formation of defects in CdS and CdS:Cu single-crystals irradiated by E = 46 MeV protons

The results of an experimental study of the spectral dependence of the adsorption coefficient, reflection exciton spectra, luminescence, photoconductivity (in the wavelength range from 0.45 to 1 m), and dark conductivity of pure and copper-doped CdS single-crystals, irradiated by E=46 MeV protons, are presented. It is shown that irradiation produces characteristic defects both in the cadmium sublattice and in the sulfur sublattice, but for one and the same irradiation dosages the defect concentration in CdS:Cu is many times higher than the concentration of defects in the pure crystals. A significant difference is observed in the concentrations of defects in these samples only when they are irradiated by high-energy particles which strongly ionize the lattice of the crystals. It is proposed that there exists an ionization mechanism for the transfer of a significant part of the energy of the moving protons to Cu atoms, which form a large number of defects (more than 1 per copper atom).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 62–66, May, 1987.