Solid phase equilibria in the Au-Ga-As, Au-Ga-Sb, Au-In-As, and Au-In-Sb ternaries
- PDF / 767,171 Bytes
- 9 Pages / 594 x 810 pts Page_size
- 83 Downloads / 150 Views
I. INTRODUCTION The study of thin metal films on compound semiconductors has attracted a great deal of attention in the past decade because of the interest in the electronic states that form and the behavior of the resulting Schottky barrier. '~19 In order to control the electrical properties of these systems, one must first understand the chemistry that occurs at the metal/semiconductor interface. However, despite a large amount of recent work examining the metallurgy of thin films on semiconductors, especially Au on III-V substrates, it is clear that no broad framework yet exists to explain the observations that have been reported. The earliest studies of the Au/III-V interfaces noted that "interdiffusion" of the metal and semiconductor occurred after samples were heated to relatively low temperatures (i.e., 573 K or so). 2 " 6 Later studies recognized that this diffusion was actually the result of a chemical reaction. 17 " 17 The general pattern that appears from these studies is that heating a Au film/III-V substrate system leads to the decomposition of the semiconductor near the interface and the release of volatile elemental group V through the grain boundaries of the metal film.9 Such behavior can be rationalized, since the Pauling electronegativity of Au is higher than that of the group V elements.20 Thus Au acts as an oxidizing agent and displaces the less electronegative group V elements in combining with the highly electropositive group III metals. Although such a picture is consistent with experimental observations, it does not have any predictive value. As Schwartz has shown,21"23 a necessary step in understanding the chemistry of thin oxide films on compound semiconductors was the study of the O-III-V ternary phase diagrams. Very little work on bulk A u III-V phase diagrams has been performed previous to this examination, but the paper of Panish24 on the bulk 352
J. Mater. Res. 1 (2), Mar/Apr 1986
http://journals.cambridge.org
Au-Ga-As system provides a background for the study of Au films on GaAs. Panish's results indicated that bulk Au and GaAs are not thermodynamically stable with respect to one another, and that the ternary phase diagram was rather complex. Although he did not map the phase diagram in detail, he did determine that both AuGa and AuGa 2 , intermetallic compounds formed pseudobinary cuts with GaAs through the ternary phase diagram. This observation is important in that it shows what pure metallic phases are thermodynamically stable with respect to GaAs, since in general the phase rule would predict that there should be three solid phases in equilibrium for a system made up of three elements (in the absence of any constraints other than fixed temperature and pressure). 25 The purpose of this work is to extend the studies of Panish24 and to examine the Au-Ga-Sb, Au-In-As, and Au-In-Sb systems along the lines of the phase diagram investigations of Schwartz.21"23 The intention is not to map the phase diagrams in great detail, but rather to determine which metallic phases are stable wi
Data Loading...
