[en] Five brown natural type IIa diamonds were found to contain concentrations of trapped monovacancy-type defects and large vacancy clusters that significantly exceed the vacancy content in colourless natural or synthetic type IIa diamonds. A proprietary heat-treatment reduced the vacancy cluster content by about 50% and removed the brown colour. The origin for the brown colour is associated with highly distorted regions

[en] A new method is proposed to deal with analysis of positron annihilation lifetime spectra which defy ordinary computer fitting. The method is particularly suited for investigations of defects in metals. (Auth.)

[en] The contribution of backscattered, 1.27-MeV γ quanta to the coincidence counts in positron-annihilation lifetime measurements has been investigated. Depending on the energy window settings and geometry, as much as 20% of the coincidence counts was found to arise from backscattered events. Computer analysis of such spectra leads to erroneous results. Analysis of computer-generated lifetime spectra shows that good statistics is more important than good resolution power for the quality of analysis. (orig.)

[en] We have developed a simplified model for the trapping of positrons by negatively charged vacancies. By solving the differential equations pertaining to the population of positron states, expressions for the experimentally observable positron parameters (lifetimes, their intensities and the Doppler broadening parameter S) were obtained. We show that the temperature dependencies of the positron parameters are markedly influenced by the ratio between the trapping rate from the delocalized state to the vacancy and that from the Rydberg-like state to the vacancy. We illustrate the usefulness of the model in the case of Doppler broadening data for diamond

[en] Positron lifetimes for the ten semiconductors Si, Ge, α-Sn, GaP, GaAs, GaSb, InP, InAs, InSb, and CdTe as well as for diamond and SiC have been measured. The bulk-annihilation rates range from 8.7 ns^-1 for diamond to 3.44 ns^-1 for CdTe and agree well with theoretical calculations. The effect of doping of GaAs was investigated with four different concentrations of Si and of Cd and Cr. In contrast to Si, significant doping effects are present in GaAs. (author)

No abstract available

No abstract available

[en] Positron annihilation is a new addition to the techniques capable of furnishing microscopic information on defects in semiconductors. The present state of the art of annihilating positrons will be briefly reviewed. Recent high temperature measurements on silicon will be discussed in detail with the aim of demonstrating the capabilities of this method as well as demonstrating the kinds of assumptions necessary for arriving at numerical values for, say, vacancy formation enthalpies. The consequences of the positron annihilation experiments on diffusion mechanisms will also be considered. (author) 5 figs., 35 refs

[en] In this review the merits of positron annihilation for investigating defects in semiconductors will be discussed. Comparison will be made with ''standard'' methods such as electron paramagnetic resonance, infrared spectroscopy and deep level transient spectroscopy as applied to various semiconductors. In the case of silicon (only) the available detailed knowledge from the ''standard'' methods will be compared to the positron data addressing the association of lifetime values with specific defect structures such as monovacancies and divacancies. The importance of charged states (Fermi level position), shallow traps and impurity-vacancy complexes will be emphasized. Trapping cross-sections for various defects/charged states will be discussed in the context of electron paramagnetic resonance data. (author)

[en] During the last few years wide interest is generated in applying the positron annihilation techniques to defects in semiconductors. Since defects in semiconductors are, in many regards, dissimilar to defects in metals one must expect that new responses from positrons will emerge not normally associated with metals. One such important effect would be the charged state of a defect in a semiconductor. At the present time silicon is the semiconductor which has been investigated mostly, but the important III-V GaAs compound semiconductor is currently also under intensive investigations. For the case of silicon a detailed review will be presented encompassing lifetime results for vacancy agglomerates, high-temperature equilibrium measurements (undoped and P-doped) and oxygen in silicon. Furthermore, indications for the temperature variation of the bulk lifetime and its possible variation with doping levels will also be discussed. (author)