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Title: Analytical electron diffraction from III-V and II-VI semiconductors
Author: Spellward, Paul
ISNI:       0000 0001 3473 8538
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 1990
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This thesis describes the development and evaluation of a number of new TEM-based techniques for the measurement of composition in ternary III-V and II-VI semiconductors. New methods of polarity determination in binary and ternary compounds are also presented. The theory of high energy electron diffraction is outlined, with particular emphasis on zone axis diffraction from well-defined strings. An account of TEM microstructural studies of CdHg1-, Te and CdTe epitaxial layers, which provided the impetus for developing the diffraction-based analytical techniques, is given. The wide range of TEM-based compositional determination techniques is described. The use of HOLZ deficiency lines to infer composition from a lattice parameter measurement is evaluated. In the case of CdxHg1. XTe, it is found to be inferior to other techniques developed. Studies of dynamical aspects of HOLZ diffraction can yield information about the dispersion surface from which a measure of composition may be obtained. This technique is evaluated for AIXGal_XAs, in which it is found to be of some use, and for CdXHg1. Te, in which the large Debye-Waller factor associated with mercury is discovered to render the method of little value. A number of critical voltages may be measured in medium voltage TEMs. The [111] zone axis critical voltage of CdxHgl_XTe is found to vary significantly with x and forms the basis of an accurate technique for composition measurement in that ternary compound. Other critical voltage phenomena are investigated. In AIXGa 1-,B As and other light ternaries, a non-systematic critical voltage is found to vary with x, providing a good indicator of composition. Critical voltage measurements may be made by conventional CBED or by various other techniques, which may also simultaneously yield information on the spatial variation of composition. The use of diffraction contrast imaging, large angle CBED and convergent beam imaging is evaluated and shown to have some advantages for flat samples. In studies of growth mechanisms, microstructures and even macroscopic properties, knowledge of the polarity of a zincblende structure crystal may be valuable. Methods of polarity determination are surveyed. Two new TEM-based techniques are described and results from a range of II-VI and III-V semiconductors are presented
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Solid-state physics