G. J. Kemerink

ANISOTROPIC RECOILLESS FRACTION AND TEMPERATURE-DEPENDENT QUADRUPOLE INTERACTION OF SUBSTITUTIONAL I-129 IN SI DUE TO JAHN-TELLER DISTORTION

Abstract A dope concentration dependent quadrupole relaxation and a large anisotropy of the recoilles fraction are observed for substitutional iodine impurities in silicon, using 129 I Mossbauer spectroscopy. The results are interpreted in terms of a transition from a static to a dynamic Jahn-Teller distortion.

ISOMER-SHIFTS OF I-129 IMPURITIES IMPLANTED IN SEMICONDUCTORS

Mössbauer spectra of the 27.8 keV transition in129I have been measured with sources of129mTe implanted in α- and β-tin and α- and β-SiC. The spectra mainly show two single line components, just as those obtained in earlier investigations with sources of129mTe implanted in diamond, silicon and germanium. The component with isomer shift corresponding to a decreased s-electron density relative to the I− ion is attributed to the substitutionally implanted impurities, that with shift corresponding to an increased s-electron density to interstitial impurities. Plots of the shifts of both component show a linear dependence on the lattice constant for diamond, silicon and germanium and α-tin. For SiC, however, the shifts are considerably smaller than expected on the basis of this linear dependence. All shifts can be quantitatively understood on the basis of a simple model that attributes the shifts of the interstitial impurities to a compression in the host lattice and shifts of the substitutional impurities to the combined effect of compression and hybridized bonding.

Mössbauer spectroscopy of laser annealed tellurium implanted silicon (II).129I

Laser annealed129mTc-implanted silicon has been investigated using129I Mössbauer spectroscopy. At least three dopedependent charge states of substitutional iodine are found. For heavily doped p-type Si a single line component S1, with isomer shift S=0.96(4) mm/s w. r. t. Cu129I and an effective Debye temperature ϕ′=196(3) K is observed. This component is attributed to I++. For compensated Si a single line component, S2, assigned to I+, with S=2.39 (4) mm/s and ϕ′=170 (3) K is found. For n-type Si, a component S3, characterized at 4.2 K by S=2.15 (4) mm/s and a quadrupole splitting eQVzz/h=452 (8) MHz (n≃0)is observed. At higher temperatures S3 shows quadrupole relaxation and its recoilless fraction becomes strongly anisotropic. This behaviour is explained on the basis of a transition from a static to a dynamic Jahn-Teller distortion. Component S3 has been attributed to I0. In the spectra of compensated and n-type Si a less well-defined component Q, with parameters resembling those of S3 but showing no quadrupole relaxation, is observed. This component has tentatively also been assigned to Io. The results can be understood qualitatively on the basis of a simple MO-model.

TELLURIUM IN SILICON .1. CHANNELING AND RUTHERFORD BACKSCATTERING STUDIES OF TELLURIUM IMPLANTED SILICON

Abstract After pulsed ruby laser annealing of tellurium implanted silicon considerable impurity redistribution is observed with little surface segregation. In the bulk, substitutional fractions of 85-90% are found, independent of the Te-concentration or the presence of phosphorus or boron. Computer simulations show that the slight narrowing of the Te-yield curves can be accounted for by the Te-vibrational amplitudes. The displacement cross-section of substitutional Te-atoms in laser annealed silicon for 2 MeV He+-ions is determined as 5.6(20) × 10−21 cm2. In contrast to pulsed laser annealing, oven annealing results in strongly narrowed Te-yield curves with a high minimum yield, indicating a small true substitutional impurity fraction.

HYPERFINE INTERACTION AND CHANNELING STUDIES OF IMPURITIES IMPLANTED IN SILICON

Abstract The combination of hyperfine interaction and channeling studies may provide a profound insight into the location and the electronic state(s) of certain impurities implanted in semiconductors. This is demonstrated for impurities of Sn, Te and I in silicon, using Mossbauer spectroscopy of implanted and laser annealed sources of different radioactive Te-isotopes and channeling studies on samples of Si implanted with stable Te and I isotopes. For Te and I impurities, a clear dependence of the Mossbauer isomer shift on semiconductor doping (n + , compensated or p + ) is found. This implies the existence of different impurity charge states. Moreover, for iodine a charge state dependent distortion of the impurity cell is observed, which is interpreted as a Jahn-Teller distortion.

Mössbauer spectroscopy of laser annealed tellurium implanted silicon (I).119Sn and125Te

Laser annealed Te-implanted silicon has been investigated using119Sn and125Te Mössbauer spectroscopy. The119Sn Mössbauer spectra consist of a single lorentzian, known to be due to substitutional Sn atoms in Si, independent of the type of doping of the silicon. The results on125Te revcal at least two different components. In heavily doped n-type Si a single line component is observed with an isomer shift of 0.15 (5) mm/s with respect to SnTe and an effective Debye temperature of 207 (3) K. Heavy p-doping leads to another single line component with an isomer shift of −0.13 (5) mm/s and an effective Debye temperature of 232 (3) K. These components are ascribed to the neutral and doubly positive charge state of substitutional Te atoms, respectively.

TELLURIUM AND IODINE IN SILICON .2. HALL-EFFECT AND RESISTIVITY MEASUREMENTS ON ION-IMPLANTED SILICON

Abstract The fraction of substitutional Te atoms in silicon deduced from temperature dependent Hall measurements is comparable to that derived from channeling experiments. The donor activation energy of these atoms is found to be about 0.19 eV. Approximately 10% of the Te-atoms give rise to a shallow donor level at Ec -0.06 eV and is probably associated with a defect. Substitutional iodine is not electrically active in Si up to 450 K. From this a lower limit of the donor activation energy of 0.30 eV is estimated.

CHANNELING AND RUTHERFORD BACKSCATTERING STUDIES OF IODINE-IMPLANTED SILICON

Abstract Iodine-implanted silicon has been investigated after laser and oven annealing using the channeling/ RBS technique. Both laser and oven annealing result in good epitaxial recovery of the implanted Si-layer. The fraction of I-atoms on (near-)lattice sites exceeds 95% after oven annealing at 875 °C. After annealing with a Q-switched ruby laser this fraction is much lower. Angular scans for an oven annealed sample containing I only give yield curves that are considerably narrowed. Continuum string simulations show that this can be explained by assuming that the I-atoms are displaced from substitutional sites over a distance of ≳ 0.15 A. For a boron doped sample the yield curve is found to be less narrowed. These results are in qualitative agreement with conclusions previously drawn from 129I-Mossbauer spectroscopy. The difference in lattice location is attributed to a charge state dependence of the symmetry of the the impurity configuration.

DEBYE-WALLER FACTORS OF I-129 IN CUI, SNTE, ZNTE AND THE ALKALI IODIDES LIL, NAI, KI, RBI AND CSI DETERMINED BY MOSSBAUER-SPECTROSCOPY

Debye-Waller factors in the temperature range 4.2 to 250K have been determined for the alkali iodides and for some standard sources and absorbers for 129I Mossbauer spectroscopy. The results for the alkali iodides are compared with predictions based on various lattice dynamical models. Satisfactory agreement in most but not in all cases exists for the nearest-neighbour interaction model of Kagan and Maslov (1962), the 11-parameter shell model of Cowley et al. used by Gupta (1975) and the deformation dipole model of Hardy used by Jaswal (1966) and by Hardy and Karo (1979).

MOSSBAUER STUDIES OF KR-83 IMPLANTED IN SEMICONDUCTORS AND METALS

Mössbauer spectroscopy of the 9.4 keV transition in83Kr has been performed using sources of83Rb implanted in the group IV semiconductors diamond, silicon, germanium and tin and in the metals Cu, Ag, Au, Mo and W. From the line widths and isomer shifts information has been obtained on possible lattice sites of the impurities. In most cases a site with large isomer shift, thought to correspond to a compression of the krypton atom was observed. This site is interpreted to represent purely substitutional impurities. In Mo and W a well-defined vacancy release stage was observed, leading to a reduction of the isomer shift and a line broadening.