In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open‐volume‐type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si‐based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.

Characterization of defects in Si and SiO2−Si using positrons

Positron annihilation spectroscopy (PAS) is a novel method that provides molecular-level information about complex macromolecular structure in a manner different from, but complementary to, conventional physical and chemical methodology. This paper presents a perspective of PAS in polymeric systems covering 12 aspects: historical, spacial, spherical quantum model, anisotropic structure, voids, positronium chemistry, time, positron annihilation lifetime spectroscopy and data analysis, variable monoenergetic slow positron beam techniques and depth profiling, elemental analysis, multidimensional instrumentation advances in PAS, and free volume and free-volume theories.

Perspective of Positron Annihilation Spectroscopy in Polymers

ROLE OF VACANCY-SOLUTE COMPLEX IN THE INITIAL RAPID AGE HARDENING IN AN Al-Cu-Mg ALLOY

Studies of light alloys by positron annihilation techniques

Doppler-broadening measurements of the electron–positron annihilation line in twenty-seven single-element samples are presented. A coincidence technique has been used to suppress the background and to evidence the contribution of positron annihilation with core electrons. Systematic dependences on the atomic number of the target material are found in ratio curves obtained dividing the measured spectra by the spectrum of a reference material. The positron lifetime technique has been used to detect the presence of positron traps in all the samples. The change in the highmomentum part of the annihilation line due to positron trapping is illustrated. The measured data are in a good qualitative agreement with recent theoretical calculation and constitute the most complete measurement series, up to now, to establish a future data-base for positron annihilation spectroscopy. 2002 Elsevier Science B.V. All rights reserved.

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Doppler-broadening measurements of positron annihilation with high-momentum electrons in pure elements

The momentum profiles from positron annihilation with core electrons in Al have been observed with a recently developed two-detector Doppler-broadening technique. Independent-particle-model (IPM) calculations are in good agreement with the experimental results beyond twice the Fermi momentum and suggest the absence of strong positron-electron correlation effects in this region. Comparisons of calculations with properly normalized momentum profiles indicate that high-momentum core contributions may provide information on the nature of vacancy-type defects and self-trapping effects.

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Positron-annihilation momentum profiles in aluminum: Core contribution and the independent-particle model

A two-dimensional Doppler broadened technique in positron annihilation

Certain types of x‐ray experiments require very precise angular positioning of crystals in the vicinity of the Bragg reflection condition. A system applicable to some measurement of this type is described which achieves a long‐term angular stability of ∼10−7 radians, coupled with a linear angular readout. This is achieved through a novel capacitance sensing system which provides angle measurement, together with the use of an auxilliary servo loop based on the Bragg condition to ensure long‐term overall angular stability.

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A capacitance-based micropositioning system for x-ray rocking curve measurements.

Lattice-location studies of argon, potassium, and calcium in iron

The problems of pulse on pulse pile-up and noise limited pile-up rejectors are considered in detail for Rutherford backscattering spectra. The form of these spectra allow the distortions from pile-up and the residual pile-up after rejection to be understood via a simple model. Extended calculations allow us to predict the effects quite accurately. A new pile-up rejection system is described. The "linear" rejection method is implemented with peak stretchers and advantageously combined with an event counting rejector to provide a versatile high performance system.

R. A. Boie

Papers

Positron-annihilation momentum profiles in aluminum: Core contribution and the independent-particle model

A two-dimensional Doppler broadened technique in positron annihilation

A capacitance-based micropositioning system for x-ray rocking curve measurements.

Lattice-location studies of argon, potassium, and calcium in iron

A Hybrid Pulse Pile-Up Rejection System as Applied to Rutherford Backscattering