Positron Studies of Defects in Thin Films and Semiconductors

Abstract

Positron studies of defects in thin films and semiconductors are reviewed. The resultsobtained from experimental studies of Doppler broadening of annihilation radiation (DBAR)from variable energies are presented. Normalisation methods for the DBAR parameters S andW have been developed, allowing for direct comparisons of the results for different samplestaken over long periods of time. The evaluation of the P:V parameter, the peak-to-valley ratioin a full annihilation spectrum, has been improved via a correction method that produced afourfold increase in sensitivity to o-Ps annihilation. The spectrum ratio curve technique wasimproved and developed to investigate the chemical composition of the environmentsurrounding a positron-trapping defect. By fitting to multiple-element and/or defect-typeresponses the percentage of that particular element or defect contained within the samplecould be found. Ratio curves were found to rely on the positron affinity to different vacancytypes. Beam-based Doppler broadening spectroscopy, variable-energy positron annihilationspectroscopy (VEPAS), was used as a probe of oxide film and film/substrate interfacecharacteristics. Different film growth methods were found to play a significant role indefining the features of films and their interfaces. Vacancies have a profound effect on theproperties of semiconductor-type devices. A range of different structures and the effects ofimplantation have been investigated. VEPAS has been found to be useful in studying themore exotic types of materials, silica aerogel and niobium.

Date of Award	22 May 2013
Original language	English
Awarding Institution	University of Bath
Supervisor	Paul Coleman (Supervisor)