P.J.M. Smulders

Indium contamination from the indium-tin-oxide electrode in polymer light-emitting diodes

We have found that polymer light‐emitting diodes (LEDs) contain high concentrations of metal impurities prior to operation. Narrow peaks in the electroluminescence spectrum unambiguously demonstrate the presence of atomic indium and aluminum. Rutherford backscattering spectroscopy (RBS) and x‐ray photoelectron spectroscopy (XPS) depth profiling data corroborate this result. An average indium concentration of 5×1019atoms/cm3 originating from the indium–tin–oxide (ITO) electrode has been found in the polymer layer.

COMPUTER-SIMULATION OF CHANNELING IN SINGLE-CRYSTALS

Abstract A Monte Carlo program for the calculation of channeling phenomena is described. The program combines the binary collision model and the multistring approximation. The energy loss due to electronic excitation is taken into account, with the use of the model of Dettmann and Robinson for the inner-shell electrons and the theory of Pines for valence electrons. The output of the Monte Carlo program may be used for the determination of the impurity sites in single crystals, via a set of auxiliary programs, that enable that calculation of the impurity yield and the analysis of experimental channeling dips. As an application, the site determination of iodine in silicon is described. Another application is the simulation of RBS spectra of planar channeling ions. Simulated and experimental spectra are compared for 1 MeV ions in the (110), (111) and (100) planes of silicon. A reasonable agreement was found. The possible causes of the remaining deviations are discussed.

Lattice site location of Te in GaAs

Abstract The lattice site of donor Te atoms in GaAs was studied by the channeling technique in order to determine the position of the nonsubstitutional fraction. Single crystals of pure GaAs with a (100) orientation were implanted with 220 keV Te ions to a dose of 3 × 1014 cm−2. After rapid thermal annealing (820°C, 15 s) angular scans through three major axial directions were measured with 3.9 MeV He+ ions. A strong asymmetry, observed in 〈110〉 scans along a (211) plane, is discussed and quantitatively explained by Monte Carlo simulations. Analysis of the data for Te, by comparison with computer simulations, shows that practically all Te atoms are close to As sites, with an average displacement of 0.32 ± 0.04 A . A clear separation in a substitutional fraction and a nonsubstitutional fraction at a unique site is not evident. The best overall fit for the Ga + As RBS spectra was obtained for thermal vibration amplitudes corresponding to a Debye temperature of 260 ± 10 K.

Simulation analysis of ion channeling spectra: thermal vibrational amplitude in Si

Abstract Energy spectra for 1 MeV He ions scattered by a Si single crystal over an angle of 58° were measured for incident directions along the 〈110〉 string and a number of directions 4° off the string: {100}, {110} and {111} planes as well as three non-channeling directions. The measurements were performed at a temperature of 164 K, under glancing-exit-angle conditions. The experimental spectra were reproduced by Monte Carlo simulation, and a x 2 analysis procedure was developed to determine the thermal vibrational amplitude in Si. Two ion-atom potentials used in the calculations (the ZBL potential and a Hartree-Fock potential) yielded essentially the same amplitude of 0.066(2) A. The corresponding Debye temperature of 490(15) K agrees well with recent determinations by other methods.

The relation between depth and energy in channeling experiments

Spectra of protons backscattered from a silicon single crystal were measured at a bombarding energy of 2300 keV. A narrow resonance in the elastic scattering cross sections of protons from 28Si, at 2090 keV, shows up as a peak in the spectra. The position and the shape of this peak were found to vary when the beam alignment was changed from a random to an axial or planar crystal direction. These effects are attributed to a different energy loss distribution of the incoming protons in these three cases. The measured spectra were compared with spectra obtained from Monte Carlo simulations in which the dependence of the energy loss on the impact parameter of the collision is taken into account. The measured and simulated spectra were found to agree qualitatively. By analysing the energy loss of the simulated trajectories, conclusions are drawn about the influence of the reduced energy loss in channeling directions on the energy to depth conversion in channeling experiments.

Lattice site location of clustered boron atoms in silicon

Si crystals were doped with 11B by ion implantation followed by ruby laser annealing. Displacement of B atoms from lattice sites was induced by proton irradiation at 35 K, followed by thermal annealing at 300 K. The resultant defect configuration was studied by ion channeling. Angular scans for Si and B were measured through several major axes, for irradiated samples, before and after the anneal, using RBS and the 11B(p, α)8Be reaction at Ep = 0.7 MeV. The experiments were compared with simulated scans, calculated with the use of both Monte Carlo and analytical methods, for a variety of assumed lattice sites. The results show that the fraction of displaced B atoms increases from ≈ 15% to ≈ 40% by the annealing process. The lattice site of these B atoms may either be a position displaced by 0.85 A along the 〈110〉 direction, or 0.9 A along the 〈100〉 direction, or a combination of positions, such as a fraction shifted in the 〈100〉 direction and a fraction at the bond center position. Despite considerable differences in the shape of channeling profiles predicted by the two models used, the results regarding the lattice position of the B atoms are consistent.

Giant focusing peak and potential dependence observed in a transition from axial to planar channeling in Si

Abstract A detailed study has been made of energy spectra of 1 MeV He ions, scattered elastically under grazing exit conditions, in silicon at a temperature of 164 K. The spectra, measured during an angular scan through the axis, in a (211) plane, show a very rich structure. Most notable is a very strong focusing peak with a height of 2.5 times the random level, that occurs at a tilt angle of 1° with the axis. The shape and the intensity of each of the spectra were compared with simulations, using two independently developed Monte Carlo simulation programs. The analysis showed that details of the spectra are quite sensitive to the assumed ion—atom potential. Major discrepancies occur when the ZBL potential is used. A considerable improvement is obtained by the use of a Hartree—Fock potential. A few other models of the ion—atom potential were also tried, and the results compared.

Copper implantation defects in MgO observed by positron beam analysis, RBS and X-TEM

In this work, eAects of copper ion implantation in MgO were studied. (1 0 0) MgO samples were implanted with 50 keV Cu ions and thermally annealed stepwise in air for 30 minutes at 550, 750, 1000, 1250 and 1350 K. After ion implantation and after each annealing step, the samples were analysed with positron beam analysis (PBA). Use was also made of Rutherford backscattering spectrometry/channeling (RBS-C) and cross-sectional transmission electron microscopy (X-TEM). The combination of these techniques enabled to monitor the depth resolved evolution of both created defects and the copper atom depth distribution. PBA results show that copper implantation at a dose of 10 15 ions cm ˇ2 yields a single layer of vacancy type defects after annealing. However a copper implantation at a dose of 10 16 ions cm ˇ2 clearly yields two layers of defects in the material after annealing, separated by an intermediate layer. In both layers nanocavities have been identified. RBS experimental results show that the implanted copper atoms diAuse into the bulk material during annealing. X-TEM and channeling results show that after annealing, the lattice of the copper nanoprecipitates is epitaxial to the MgO host lattice. Under some circumstances, copper precipitates and small voids can co-exist. Furthermore, X-TEM measurements show that the nanocavities have rectangular shapes. ” 2000 Elsevier Science B.V. All rights reserved.

Random spectrum for the channeling-backscattering technique: A rotating axial-dip study

The (100) axial channeling dip for a Si single crystal, obtained by averaging over azimuthal angles, is studied experimentally and by Monte Carlo simulation for tilt angles theta up to 16-degrees using a 1.5 MeV energy He-4+ ion beam. Both in the experiment and the simulation, the dip shape is found to be in a quantitative agreement with the rule of angular compensation; the influence of the (100) axis extends to theta almost-equal-to 6-degrees. Surprisingly strong fine structure in the yield, with a number of distinct secondary dips, is observed for theta > 6-degrees. It is shown that this structure is related to some high-index crystallographic planes being nearly tangent to the azimuthal scans at certain tilts. Good agreement between the experiment and simulation is obtained at all tilt angles investigated. Consequences for the random yield determination in channeling studies are discussed.

Azimuthally averaged backscattering yield near the 〈100〉 axis in Si

Abstract An azimuthally averaged backscattering yield near the 〈100〉 axis in Si is studied experimentally and by Monte Carlo simulation, for 1.5 MeV 4He ions and tilt angles θ up to 16°. A complete compensation of the 〈100〉 dip is obtained within 0° ⩽ θ⩽ 6°, in agreement with the rule of angular compensation. For larger tilts a fine structure in the yield, with a number of distinct secondary dips, is observed. The results of two simulation programs (CXX and FLUX) are found to be fully consistent with each other, and in excellent agreement with the experimental data. The extension of the simulation methods to include trajectories that substantially deviate from the string direction is presented.