Point-defect mediated diffusion in intrinsic SiGe-alloys

The aim of this thesis was to obtain fundamental diffusion data and to improve the understanding of point-defect mediated dopant diffusion in Si1- xGex alloys. The thesis consists of experimental studies published in international journals and a summary section. The experimental part consists of the following four articles: In article I, diffusion coefficients and Arrhenius parameters have been determined in relaxed intrinsic Si1-xGex in the whole concentration range (0<x<1). In article II, diffusion coefficients and Arrhenius parameters have been determined for Ga and Sn diffusion in relaxed intrinsic and relaxed heavily p-doped germanium. In article III, diffusivity values have been determined for Ga in relaxed intrinsic Si1-xGex in the whole concentration range at 907 ºC. In article IV, diffusion coefficients and Arrhenius parameters have been determined for Si in intrinsic B20-structured FeSi. All the experiments discussed employed the modified radiotracer technique. The radioactive tracers were produced at the IGISOL facility located in Jyväskylä, Finland (31Si and 66Ga) and at the ISOLDE facility located in CERN, Switzerland (123Sn). In the summary section, an attempt has been made to understand the diffusion behavior of substitutionally solved group III, IV and V elements in Si1-xGex alloys based on point-defect transport capacities and properties of pointdefect- impurity interactions. The dissection is based on best available literature data as well as the data obtained during this study (articles I-IV)

Mobility determination of lead isotopes in glass for retrospective radon measurements

In retrospective radon measurements, the 22-y half life of 210Pb is used as an advantage. 210Pb is often considered to be relatively immobile in glass after alpha recoil implanted by 222Rn progenies. The diffusion of 210Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if 210Pb is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where 209Pb was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the 209Pb atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470–620°C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 ± 0.2 eV, and also the pre-exponential factor D0, in the order of 20 m2s−1. This result confirms the assumption that over a time period of 50 y 209Pb (and 210Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of 209Pb in the topmost surface at high temperatures

Retention of Pb isotopes in glass surfaces for retrospective assessment of radon exposure

In recent years there has been increasing interest in radio-epidemiological techniques to retrospectively measure the radon dose exposure by determining the activity of 210Pb, the longest-lived 222Rn progeny, in glass surface layers. In this study the diffusion of 39 keV 209Pb+ ions implanted into glass using the IGISOL facility has been studied under conditions that mimic the recoil implantation of 210Pb from 222Rn. The resulting depth distributions of 209Pb were then measured after heat treatment in vacuum at different temperatures by a sputter erosion technique. The diffusion coefficient could be described by an Arrhenius equation D = D0exp(−H/kT) where and H = 2.81 ± 0.11 eV. No statistically significant loss of 209Pb from the sample was observed for annealing between 470 and 600 °C