Iiro Riihimäki - Academia.edu (original) (raw)

Papers by Iiro Riihimäki

Physical Review B, 2003

ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers... more ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers. The properties were studied as a function of composition x for the full range of materials with x=0, 0.20, 0.35, 0.50, 0.65, 0.8, and 1. The activation enthalpy Ea was found to drop systematically from 3.8 eV (x=0) to 2.4 eV (x=1). Comparisons with other impurity atom- and self-diffusion results in Si, Ge, and SiGe show that both interstitials and vacancies contribute as diffusion vehicles in the composition range 0<~x<~0.35 and that vacancy mechanism dominates diffusion in the composition range 0.35<x<~1.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

Radiation Protection Dosimetry, 2008

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)... more In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb 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 (209)Pb 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 (209)Pb 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 degrees 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 D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.

Physical Review Letters, 2002

ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studie... more ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studied in the tempera­ture range 730-950 °C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6eV and 3.5eV and preexponential factors of 7.5×10-3 m2 s-1 and 8.1×10-3 m2 s-1 for 31Si and 71Ge, respectively. These results suggest that, as in Ge, in Si0.20Ge0.80 both 31Si and 71Ge diffuse via a vacancy mechanism. Since in Si0.20Ge0.80 71Ge diffuses only slightly faster than 31Si, in self-diffusion studies on Si-Ge 71Ge radioisotopes may be used as substitutes for the ``uncomfortably'' short-lived 31Si radiotracer atoms.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004

ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed... more ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed. They include energetic light particles ensuring radioactive isotope production via nuclear reactions, keV-ion implantation of radiotracers and sputtering by low energy heavy ions for depth profiling. If the involved ion–solid interactions are properly taken into account, the technique provides an effective means for solid-state diffusion studies under demanding conditions. The various aspects related to the modified radiotracer technique are surveyed and discussed. The reliability of the procedure is demonstrated by comparisons with corresponding profiles obtained by secondary ion mass spectrometry. Also previously unpublished diffusion data for 71Ge self-diffusion in relaxed Si0.87Ge0.13 are provided for comparison purposes.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24Ge... more We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24GeV/c and 10MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003

ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardne... more ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardness of silicon detectors. In this study, oxygenated and non-oxygenated silicon samples were processed and irradiated with 15MeV protons. In order to speed up the defect reactions after the exposure to particle radiation, the samples were heat treated at elevated temperatures. In this way, the long-term stability of silicon detectors in hostile radiation environment could be estimated. Current–voltage measurements and Surface Photovoltage (SPV) method were used to characterize the samples.

IEEE Transactions on Nuclear Science, 2002

ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Ox... more ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.

Philosophical Magazine, 2004

Physical Review B, 2003

ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers... more ABSTRACT The intrinsic As diffusion properties have been determined in relaxed Si1-xGex epilayers. The properties were studied as a function of composition x for the full range of materials with x=0, 0.20, 0.35, 0.50, 0.65, 0.8, and 1. The activation enthalpy Ea was found to drop systematically from 3.8 eV (x=0) to 2.4 eV (x=1). Comparisons with other impurity atom- and self-diffusion results in Si, Ge, and SiGe show that both interstitials and vacancies contribute as diffusion vehicles in the composition range 0<~x<~0.35 and that vacancy mechanism dominates diffusion in the composition range 0.35<x<~1.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006

Radiation Protection Dosimetry, 2008

In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)... more In retrospective radon measurements, the 22-y half life of (210)Pb is used as an advantage. (210)Pb is often considered to be relatively immobile in glass after alpha recoil implanted by (222)Rn progenies. The diffusion of (210)Pb could, however, lead to uncertain wrong retrospective radon exposure estimations if (210)Pb 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 (209)Pb 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 (209)Pb 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 degrees 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 D(0), in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y (209)Pb (and (210)Pb) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of (209)Pb in the topmost surface at high temperatures.

Physical Review Letters, 2002

ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studie... more ABSTRACT Self-diffusion of implanted 31Si and 71Ge in relaxed Si0.20Ge0.80 layers has been studied in the tempera­ture range 730-950 °C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6eV and 3.5eV and preexponential factors of 7.5×10-3 m2 s-1 and 8.1×10-3 m2 s-1 for 31Si and 71Ge, respectively. These results suggest that, as in Ge, in Si0.20Ge0.80 both 31Si and 71Ge diffuse via a vacancy mechanism. Since in Si0.20Ge0.80 71Ge diffuses only slightly faster than 31Si, in self-diffusion studies on Si-Ge 71Ge radioisotopes may be used as substitutes for the ``uncomfortably'' short-lived 31Si radiotracer atoms.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004

ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed... more ABSTRACT In the modified radiotracer technique ion beams within a broad energy range are employed. They include energetic light particles ensuring radioactive isotope production via nuclear reactions, keV-ion implantation of radiotracers and sputtering by low energy heavy ions for depth profiling. If the involved ion–solid interactions are properly taken into account, the technique provides an effective means for solid-state diffusion studies under demanding conditions. The various aspects related to the modified radiotracer technique are surveyed and discussed. The reliability of the procedure is demonstrated by comparisons with corresponding profiles obtained by secondary ion mass spectrometry. Also previously unpublished diffusion data for 71Ge self-diffusion in relaxed Si0.87Ge0.13 are provided for comparison purposes.

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2004

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006

We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24Ge... more We have irradiated Czochralski silicon (Cz-Si) and Float Zone silicon (Fz-Si) detectors with 24GeV/c and 10MeV protons. Samples were characterized with Capacitance-Voltage measurements (CV), Transient Current Technique (TCT) and secondary electron backscattering recorded by Scanning Electron Microscope (SEM). We present the evolution of the effective doping concentration as a function of irradiation fluence as well as the introduction rate of

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003

ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardne... more ABSTRACT Introducing oxygen into the silicon material is believed to improve the radiation hardness of silicon detectors. In this study, oxygenated and non-oxygenated silicon samples were processed and irradiated with 15MeV protons. In order to speed up the defect reactions after the exposure to particle radiation, the samples were heat treated at elevated temperatures. In this way, the long-term stability of silicon detectors in hostile radiation environment could be estimated. Current–voltage measurements and Surface Photovoltage (SPV) method were used to characterize the samples.

IEEE Transactions on Nuclear Science, 2002

ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Ox... more ABSTRACT The effect of oxygenation on the radiation hardness of silicon detectors was studied. Oxygen-enriched and standard float-zone silicon pin-diodes and oxidized samples were processed and irradiated with 15-MeV protons. After the irradiations, the surface photovoltage (SPV) method was applied to extract minority carrier diffusion lengths of the silicon samples. Adding oxygen to silicon was found to improve the radiation hardness of silicon. The effect was visible in minority carrier diffusion lengths as well as in reverse bias leakage currents. The suitability of SPV method for characterizing irradiated silicon samples was proved.

Philosophical Magazine, 2004