Thermodynamic analysis of the deposition of GaAs epitaxial layers prepared by the MOCVD method

Abstract On the basis of a detailed thermodynamic analysis of the Ga-As-C-H system, the initial conditions have been determined, under which the reaction of trimethylgallium (TMGa) and arsine in a hydrogen atmosphere produces a single condensed phase — solid GaAs. Liquid gallium with a small amount of dissolved arsenic is formed simultaneously when the initial ratio of the elements is B V A III , whereas solid graphite is simultaneously deposited at a high initial concentration of TMGa, especially at an elevated temperature and a decreased pressure. The equilibrium concentrations of the gaseous substances are strongly influenced by the initial B V A III ratio. As 2 , As 4 , and CH 4 are the dominant species if B V A III > 1 , while CH 4 , GaCH 3 , GaH and GaH 2 are the most abundant if B V A III . The calculated deposition diagrams are in good qualitative agreement with experimental results published in the literature. A comparison of the calculated composition of the gaseous phase and the results of experiments under the conditions used for the deposition of GaAs epitaxial layers leads to the conclusion that the course and results of the deposition process are significantly affected by transport and kinetic phenomena.