High-pressure high-temperature structural studies of binary semiconductors

• Main Author: Vanpeteghem, Carine B.
• Published: University of Edinburgh 2000
• Subjects: 537.622
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663186

The last decade has seen a tremendous improvement in high-pressure diffraction techniques. Among other things, this has led to a completely new understanding of the structural systematics of the group IV, III-V and II-VI semiconductors. Many phases have been shown to have more complex, lower-symmetry, high-pressure structures than previously thought. One of the most surprising discoveries has been the non-existence of the diatomic <i>b</i>-tin structure, long believed to be one of the principal high-pressure phases of the III-V and II-VI systems. However, most of the work to date has been performed at room temperature and in fact, very little is yet known about the high-pressure phases of these systems above room temperature. The work presented in this thesis centres on the use of high temperature under pressure to investigate further the absence of the diatomic, site-ordered, <i>b</i>-tin or <i>b</i>-tin-like phases have been found but appear to be site-disordered. Additionally, the P-T phase diagrams of these systems are explored above room temperature. This work has required the development the existing high-pressure facilities on the SRS synchrotron source of Daresbury Laboratory to allow routine high-pressure high-temperature (hp/ht) experiments. These technical developments are described. High-temperature studies of GaSb under pressure reveal a new, previously unknown phase. A detailed study of the structural ordering in the hp/ht phases of GaSb is performed by combining two different experimental techniques. It is shown, by x-ray powder-diffraction, that all the hp and hp/ht phases of GaSb are site-disordered over about two unit cells or less. A complementary high-pressure EXAFS study demonstrates the absence of complete order over nearest-neighbour distances.