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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.

This paper reports a study of the nature and systematic variation of radiation damage to cuprate superconductors caused by several-hundred-MeV heavy ions. While irradiation of YBa2Cu307 q with 300-MeV Au + and 276-MeV Ag '+ ions produces columns of amorphous material along the ion trajectories, such defects are only created occasionally during irradiation with 236-MeV Cu' + and not induced with 182-MeV Si"+. A comparative study of the defect formation in Bi2Sr2Ca~Cu30 and oxygen-reduced and ozone-treated YBazCu307 z, shows that the degree of the radiation damage by the heavy ions depends on (a) the rate at which ions lose their energy in the target; (b) the crystallographic orientations with respect to the incident ion beam; (c) thermal conductivity and chemical state (oxygen concentration for YBa2Cu307 z) of the sample; and (d) the extent of preexisting defects in the crystal. A theoretical model based on ion-induced localized melting and the eA'ects of anisotropic thermal conductivity of these materials provides a basis for understanding the size and shape of the amorphous tracks. Measurements of the superconducting properties of Au +and Ag '+-irradiated YBa2Cu307 z thin films show a universal linear scaling between the fractional areal damage versus the superconducting transition temperature and the normal-state resistivity.

Superconducting critical temperatures Tc and magnetic fields Hc2, lattice parameters a0, and chemical compositions were measured for ‘‘bulk’’ layers (∼6 μm or greater) of ‘‘pure’’ and alloyed Nb3Sn which were made by the bronze process. The values of Tc, a0, and the composition of pure Nb3Sn layers were ∼18 K, 0.52900±0.00005 nm, and 25±0.5 at. % Sn, respectively, independent of heat-treatment temperature (between 650–780 °C) and of the bronze composition, as long as the thickness of the layers was greater than ∼6 μm. Small additions of Ti (∼1 at. %) or Ta (∼3 at. %) slightly increased the value of Tc (by ∼0.2–0.4 K) above that for pure Nb3Sn. However, additions of larger amounts of these elements or addition of other transition elements (V, Zr, and Mo) significantly decreased Tc. Also, small additions of these elements significantly increased Hc2. Specifically, the largest values of Hc2 (∼27 T at 4.2 K) were obtained for Nb3Sn layers containing ∼1.5 and ∼4 at. % of Ti and Ta, respectively, compared with a value for the pure Nb3Sn of 23.5 T at 4.2 K. The value of a0 decreased with all of the alloying additions; these variations can be explained qualitatively by several models for the lattice parameter of A15 compounds, but none of them can quantitatively predict the variations. In one system, (Nb,Ti)3Sn, values of the normal-state resistivity just above the transition temperature were measured: adding 3 at. % Ti raises the value to ∼55 μΩ cm from the value of 10–15 μΩ cm for pure Nb3Sn. This increase in the resistivity is thought to be a primary reason for the increased Hc2 for this system as well as the other types of alloyed Nb3Sn which were studied here.

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