Analytical electron diffraction from III-V and II-VI semiconductors.
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.
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 
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
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