SiC Polytypes Thesis

This page serves to summarise my PhD thesis, Growth and Stability of Silicon Carbide Polytypes, which is available for download.

It was completed in 1996, so parts are a little dated, but the basic principles are unchanged. A summary of the contents of its main chapters is as follows:

Chapter II

The background to polytypism in SiC. (The different polytypes arise from the different orientations in which layers of SiC can be stacked. These give rise to slightly different electronic properties: important if SiC is being used as a semiconductor substrate.)

Chapter III

A discussion of whether phonons might be expected to stabilise different polytypes at different temperatures, and whether this would lead to a phase diagram containing two phases (4H and 6H, or <2> and <3> in a different notation), three phases (adding 15R, or <23>), or an infinite number of intermediate phases forming a "devil's staircase".

The work of this chapter was published as Phonon free energy and devil's staircases in the origin of polytypes MJ Rutter and V Heine, J. Phys. - Condens. Mat. 9 2009 - 2024 (1997)

Chapter IV

High accuracy zero temperature DFT calculations, using Castep, of the electronic energy of several different polytypes of SiC. Much thought given to the cancellation of errors arising from discrete FFT grids and k-space sampling. The detailed theory here dates from the days before ultra-soft pseudopotentials, and before density mixing in the electronic minimiser.

Chapter V

High accuracy Castep calculations of the energies of a surface layer in different orientations. Much discussion of the dipole moment of a 2D slab of SiC, and how to eliminate the interactions of this dipole with its fictitious periodic images.

The work of this chapter was published as Energetics of stacking boundaries on the {0001} surfaces of silicon carbide MJ Rutter and V Heine, J. Phys. - Condens. Mat. 9 8213 - 8220 (1997)