Thermodynamic Analyses of Open Tube Germanium Disproportionation Reactions

Abstract

In order to define conditions most suitable for iodine transport of pure or gallium doped germanium, the equilibria that obtain when these elements, singly or together, are mixed with iodine or hydrogen iodide in the presence of hydrogen and/or inert gases were analyzed using computer techniques. It was found that Ge in the presence of an inert carrier gas should transport via a hot to cold process at all iodine pressures studied. These results are markedly perturbed when H2 is substituted for the inert gas due to the establishment of a competing equilibrium whose enthalpic change is opposite in sign to that of the equilibrium responsible for semiconductor transport. The effects of the competing equilibrium in turn may be modified by using a mixture of H2 and He. Under certain sets of conditions, in fact, temperature insensitive regions develop which appear to be suitable as semiconductor source and seed sites. The results for the gallium-iodine equilibrium are to a good first approximation independent of the nature of the carrier gas and indicate that hot to cold transport is to be expected over a wide range of iodine concentrations. Analyses of the three phase equilibrium in Ge-Ga-halogen systems show them to also be independent of the nature of the carrier gas. © 1964, The Electrochemical Society, Inc. All rights reserved.