A transmission electron microscopy study of the nucleation, growth and structure of epitaxial (PbSn)Te films

This dissertation reports on a study of the nucleation, growth and structure of Pb0,8Sn0,2Te films grown by the Hot Wall Epitaxial (HWE) technique onto BaF2 substrates. Following a discussion of the theoretical aspects of epitaxial growth and a detailed review of recrystallisations and reorientation processes, the experimental techniques and procedures followed are presented. Special attention is given to the techniques of transmission electron microscopy and electron diffraction as well as sample preparation. The most significant result of this work is the finding that, under certain deposition conditions, a polycrystalline film developes to a good epitaxial film with thickness. It is shown that the epitaxial overgrowth is the result, not only of epitaxial nucleation, but is also determined by recrystallisation and reorientation processes during growth. These processes are studied as a function of substrate temperature and orientation in order to explain the resultant structure of the continuous films. The defects in thin continuous films are characterised and shown to depend in nature and density on the thermal history of the complete growth cycle. The significance of the various findings is discussed in terms of epitaxial growth theories and qualitative models are developed in order to explain the experimental results