K. Bonde Nielsen

Laplace-transform deep-level spectroscopy: the technique and its applications to the study of point defects in semiconductors

We present a comprehensive review of implementation and application of Laplace deep-leve1 transient spectroscopy (LDLTS). The various approaches that have been used previously for high-resolution DLTS are outlined and a detailed description is given of the preferred LDLTS method using Tikhonov regularization. The fundamental limitations are considered in relation to signal-to-noise ratios associated with the measurement and compared with what can be achieved in practice. The experimental requirements are discussed and state of the art performance quantified. The review then considers what has been achieved in terms of measurement and understanding of deep states in semiconductors through the use of LDLTS. Examples are given of the characterization of deep levels with very similar energies and emission rates and the extent to which LDLTS can be used to separate their properties. Within this context the factors causing inhomogeneous broadening of the carrier emission rate are considered. The higher resoluti...

The antimony-vacancy defect in p-type germanium

Ge-n+p mesa diodes have been produced in 2-Ωcm single crystals using a molecular-beam epitaxy (MBE) process to grow the Sb-doped epitaxial Ge n+-top layer. The diodes are characterized by a leakage current at room temperature of 8×10−4A∕cm2 at a reverse bias of 3 V. The diodes have been used to study irradiation-induced defects in p-type Ge, in particular Sb-related defects, where Sb stems from in-diffusion during the MBE growth. Two lines in the deep level transient spectroscopy (DLTS) spectra are related to the presence of Sb. One of these lines originates from the single-acceptor state of the SbV pair with an enthalpy of ionization of ΔHp=(0.309±0.007)eV, the other from a state with an enthalpy of ionization of ΔHp=(0.095±0.006)eV, which is concluded to be the single donor-charge state of the SbV pair.

Strength functions in the β-decay of short-lived fission products

Abstract Approximate β-strength functions have been derived from measurements of the β − feed to high-lying excited states in 40 neutron-rich nuclei. These nuclei, all produced in thermal fission, cover a broad range of nuclides from bromine to yttrium (84 ≦ A ≦ 95) and from silver to lanthanum (116 ≦ A ≦ 143). The β − feed was determined by non-ideal total γ-ray absorption. Above the cut-off energy expected from pairing, the strength functions in general increase smoothly with energy when no strong allowed single-particle strength is concentrated in the observed energy range. The increase is in these cases largely proportional to the nuclear level density. When allowed single-particle strength is likely to occur the strength functions show significant structure even at higher energies (≈5 MeV) and the average strength then corresponds to a higher value of log ƒt . These data are consistent with the theory of high-energy β-decay in terms of a giant resonance, but draw attention to the persistence of significant shell structure in the tail part of the resonance although the definite but smeared-out shell-model transitions are hindered as would be expected. Direct information on the β-strength is needed for the evaluation of delayed neutron yields. The data provide such information for the wellknown delayed neutron precursors 87 Br and 137 I.

Spatial confinement and saturation of substitutional platinum by diffusion into ion‐beam damaged silicon

The diffusion of platinum into lightly damaged regions of ion‐implanted silicon has been investigated using deep‐level transient spectroscopy and capacitance‐voltage profiling. The samples consisted of PtSi/Si n‐type Schottky diodes which had been implanted with O, F, or Cl to an intermediate depth between the zero‐bias and reverse‐bias depletion boundaries, and subsequently annealed at a temperature of 700 °C. The distribution of in‐diffused Pt was obtained by monitoring the electron emission from the acceptor level (EC−ET=0.23 eV) previously assigned to Pt in a distorted substitutional configuration. The Pt was found to be distributed approximately congruous with the vacancy distribution generated during implantation. For a typical implantation dose (≊1011 cm−2) we recorded an enhanced accumulation of Pt by about two orders of magnitude as compared to diffusion into nonimplanted material. This apparent decoration of the primary damage profile occurs without the simultaneous introduction of other electri...

LAPLACE-TRANSFORM DEEP-LEVEL TRANSIENT SPECTROSCOPY STUDIES OF THE G4 GOLD-HYDROGEN COMPLEX IN SILICON

We have studied n-type silicon containing gold and gold–hydrogen complexes using high-resolution “Laplace” deep-level transient spectroscopy. This technique has enabled two quite distinct electron emission rates to be observed at temperatures between 240 and 300 K. These are associated with the gold acceptor and the level referred to as G4, which is observed when hydrogen and gold are present in silicon. The gold acceptor has a measured activation energy for electron emission of 558±8 meV, and the G4 state of 542±8 meV. The directly measured electron capture cross section for G4 is determined to be 0.6±0.1 σn(gold acceptor) at 275 K from which it is inferred that the state is acceptor-like.

M1 admixtures in transitions from γ-vibrational states in 152Sm, 154Gd and 156Gd

Abstract Measurements of M1 admixtures in a number of transitions depopulating 2, 3 + and 2, 2 + γ-vibrational states in 152 Sm, 154 Gd and 156 Gd are presented. In the case of 152 Sm, it is verified that the intrinsic static quadrupole moments of the γ band and the ground state band are equal to within 10%. It is concluded that the small M1 admixtures present in transitions between the two bands can be accounted for in first-order perturbation theory as a result of K = 1 impurities. The M1 admixture in the intraband transition 2, 3 + −2, 2 + of 152 Sm and 154 Gd is estimated and attributed to | g K − g R | ≈ 0.15 in both cases.

Perturbed angular correlations with111Cd in the α and δ phases of In-Sn

The influence on the TDPAC distribution of dissolved impurities (Sn in In) and (In in Sn) as a function of concentration has been studied at room temperature and at liquid-nitrogen temperature. Models for the observed distributions of the electric field gradients are discussed. The results are consistent with theoretical estimates of the screening charge distribution around the valency impurity.

Internal magnetic field of lutecium in iron and g factor in 175Lu

Abstract Applying γ-γ correlation techniques, the effective magnetic field at room temperature on 175 Lu in magnetized iron has been determined to be -338 ± 42 kG. With this value, the g factor of the 251 keV state in 175 Lu is measured to be g = 0.37 ± 0.12.

Magnetic hyperfine fields of119Sn in vacancy-associated defect structures in 3d ferromagnets

Defect structures associated with Sb or In impurity atoms in iron, cobalt, and nickel hosts have been detected by Sn-119 Mössbauer spectroscopy. With substitutional values as reference, the structures found are uniquely characterized by large, positive shifts in the Sn-119 magnetic hyperfine field and correlated increases in isomer shift. Further characterization are lower effective Debye temperatures. Preferably, the defects form and anneal in the resistivity stage III; the specific behaviou depending on whether Sb or In make up their kernel. They are interpreted as unique vacancy-type, relaxed structures SbVn or InVn. The vacancy trapping leads to order-of-magnitude field enhancements in fcc Co and Ni hosts, uniquely reflecting that here the substitutinal Sn fields happen to be small due to almost cancellation of large positive and negative contributions.

The E2 + M1 decay of the 2+ beta-vibrational state in 178Hf

Abstract The 1183 keV transition depopulating the 2+ beta-vibrational state in 178Hf was found to be E2 + M1 with (17 ± 10)% E2. The E2 branching ratios are shown to agree with theoretical predictions by Bohr and Mottelson.