THERMODYNAMIC ASPECTS OF THE PREPARATION OF ALAS AND GA1-XALXAS EPITAXIAL LAYERS IN HYDRIDE AND CHLORIDE SYSTEMS

On the basis of a thorough thermodynamic analysis of the Al-As-Cl-H and Al-Ga-As-Cl-H systems, feasible technological conditions for the deposition of the solid AlAs and Ga1-xAlxAs in hydride or chloride transport systems were determined. Under these conditions, there is no undesirable predeposition of the solid phase, which complicates the use of the systems for the preparation of the layers and structures containing aluminium. The calculated results were compared with the experimentally obtained values available. Further, a thermodynamic analysis of the Ga-As-Cl-H system was made. It follows, from a comparison of the calculated results that the different behaviour of the systems given is predominantly related to the different thermodynamic stabilities of aluminium and gallium chlorides in the vapour phase.