Correlation of defects and electrical properties in silicon and zinc oxide

The role of defects in semiconductor materials has become increasingly important due to the use of polycrystalline materials for device applications. The focus of this thesis is on understanding the role of extended defects, namely grain boundaries and dislocations, in commercial ZnO varistors and silicon respectively.; The excellent non-linear current-voltage characteristics of ZnO varistors are mainly attributed to grain boundary (GB) phenomena. In the ZnO portion of this work, Doppler and lifetime positron annihilation spectroscopy (DPAS and LPAS) and photoluminescence spectroscopy (PL) techniques were used, for the first time, to obtain a correlation between GB point defect equilibria and electrical degradation phenomena in commercial ZnO varistors. The Doppler S parameter, defect lifetimes and intensity components from LPAS, and PL intensities were studied as a function of composition (pure vs varistor ZnO), electrical stressing, and annealing temperature.; The PAS results are explained using the concepts of the simple trapping model, and assuming that the negatively charged zinc vacancies at the GB are the predominant positron traps. The PL spectra showed two peaks at {dollar}sim{dollar}510 nm (green luminescence) and {dollar}sim{dollar}580 nm (yellow luminescence). Luminescence intensities of the as received material were quenched by annealing, whereas they were enhanced by electrical stress. Both the PAS and PL results correlated well with each other, with current-voltage-time (I-V-t) measurements and with published results. These results are explained using GB defect reactions and are consistent with the ion migration model of varistor degradation. The theoretically predicted concentration of the various charged defects (zinc vacancies and interstitials) in different temperature regimes further support the findings of work.; In the silicon portion of this work, the role of dislocations in the aluminum gettering of process induced contaminants in single crystal Fz silicon was investigated. Dislocations were introduced by four point bend loading. The experiments were designed such that deformation and aluminum diffusion could be performed either simultaneously or sequentially (T = 1000{dollar}spcirc{dollar}C, for 3 hours). Electrical and structural characterization were performed using photoconductive decay (PCD) lifetime, etch pit and x-ray topography measurements.; Carrier lifetime was higher in the Al treated samples than in samples heat treated without Al. In some samples, lifetime increased after aluminum treatment. In the Al treated samples, the lifetime increased with increasing applied stress. This improvement was significant when the applied stress exceeded the yield stress. These results suggest a synergistic role between stress and Al gettering.