U087354.pdf (4.8 MB)
Structure and properties of amorphous GexSe1-x and related alloys.
thesisposted on 2015-11-19, 09:18 authored by Jaeho. Choi
Un-hydrogenated and hydrogenated a-GexSe1-x films (0.2 x 1) have been prepared by radio-frequency sputtering at room temperature employing an r.f. power of 240 W and an Ar pressure of 3-6 mTorr. Zn-alloyed films, a-GexSeyZnz, were deposited under the same conditions, with Zn concentrations up to 27%. The compositions of the films were determined by an energy dispersive X-ray analyser (SEM-EDAX) attached to a scanning electron microscope. Optical absorption edges of the a-GexSe1-x samples have been deduced from reflection-transmission (R-T) spectra and photo-thermal deflection spectroscopy (PDS) measurements. The optical bandgaps, other parameters related to the edges, and the real part of the refractive index were determined and analysed. The effects of hydrogenation on the a-GexSe1-x films are investigated by analysing their optical absorption edges and measurements of the d.c. electrical conductivity as a function of temperature. The optical and electrical properties of a-GexSeyZnz films were studied and the effects of Zn addition to GeSe films analysed from the behaviour of the optical gap and the activation energy in the d.c. electrical conductivity. Extended X-ray absorption fine structure (EXAFS) measurements have been performed on both a-GexSe1-x and a-GexSeyZnz films. Information on the local atomic structure, e.g. the nearest-neighbour bond length and the coordination number, has been extracted from the data and is discussed in detail. In particular, the experimentally determined partial coordination numbers are compared with those predicted by two models, the chemically ordered bond network (OBN) and random bond network (RBN) structures. The results reveal that the a-GexSe1-x films have a chemically ordered 4-2 covalent bond network structure throughout the whole composition range and that Zn replaces the Ge atoms and is four-fold coordinated. The dielectric functions of the a-GexSe1-x alloys is modelled and the calculated optical properties compared with the experimental results. Good agreement is found.
Date of award1996-01-01
Author affiliationPhysics and Astronomy
Awarding institutionUniversity of Leicester