Some titanium germanium and silicon compounds: Reaction and properties
- PDF / 1,014,950 Bytes
- 10 Pages / 593.28 x 841.68 pts Page_size
- 4 Downloads / 215 Views
I. INTRODUCTION
The subject of this paper has already been the object of two short publications1'2 that focused on the behavior of Ti with layers of pure Ge and 50-50 Si-Ge alloys on (100) Si substrates. Thus for the sake of being brief, both this introduction and the usual description of the experimental details will be kept to a minimum. In this ternary system the phases with the highest metalloid content, TiGe2 and TiSi2, have the same structure, orthorhombic (C54) with unit cell dimensions that are very close: a = 8.594 A, b = 5.030 A, c = 8.864 A, and a = 8.252 A, b = 4.783 A, c = 8.540 A, respectively.3 (One notes here some ambiguity in the literature about the respective definitions of the a and c axes so that it is not exactly clear whether the a lattice parameters are smaller than c parameters for both compounds. It will be assumed here that the axes are properly defined as presently given.) Thus with lattice parameter differences of the order of 6%, well within the limits of 15% given by the Hume-Rothery rule for
"'Permanent address: Laboratoire des Materiaux et de Genie Physique, ENSPG, BP 46, 38402 Saint Martin d'Heres, France. b) Permanent address: Thomson-CSF, Domaine de Corbeville, 91401 Orsay, France. J. Mater. Res., Vol. 5, No. 7, Jul 1990
extended solubilities between elements4 (and presumably between chemically equivalent compounds also), the two compounds should be mutually soluble, as verified2 for samples containing 50 at.% Si (and 50 at.% Ge, ignoring Ti). On the other hand, in the middle of the diagram there exists3'5'6 no exact equivalent in the Si-Ti system to the phase35'7 Ti6Ge5. Most of the investigations were carried out with layers of Ge and Si-Ge alloys deposited on (100) Si substrates via molecular beam (MBE) deposition techniques. Although these were not specifically intended to be epitaxial, they were in fact found to be so. In the results reported thus far one notes the two-stage reaction of Ti with the epitaxial layers of pure Ge: at low temperatures the formation of Ti6Ge5 with features that strongly imply a diffusion-controlled mode of growth, and quite distinctly at higher temperatures the nucleation-controlled8 formation of TiGe2. With the 50-50 Si-Ge alloy, two stages can still be recognized but the overall picture is much less clear than with pure Ge. Here attention will be focused on the behaviors of the 25-75 and 80-20 alloys, and on the electrical properties of the final disilicide-germanide solid solutions. Some relevant observations made on the reaction of Ti with single crystal Ge and on bilayers of Ti and Ge on Si will also be reported. © 1990 Materials Research Society
1453
0. Thomas, F. M. d'Heurle, and S. Delage: Some titanium germanium and silicon compounds
II. REACTION KINETICS A. Pure Ge layer and single crystal Ge
The Ti reaction with epitaxial layers of pure Ge has been sufficiently described in Refs. 1 and 2, and the results outlined in the introduction above. It will not be discussed any further here except to recall that for heat treatments of 1 h
Data Loading...
