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 an d Al-Ga-As-Cl-H systems, feasible technological conditions for the dep osition of the solid AlAs and Ga1-xAlxAs in hydride or chloride transp ort systems were determined. Under these conditions, there is no undes irable predeposition of the solid phase, which complicates the use of the systems for the preparation of the layers and structures containin g aluminium. The calculated results were compared with the experimenta lly obtained values available. Further, a thermodynamic analysis of th e Ga-As-Cl-H system was made. It follows, from a comparison of the cal culated results that the different behaviour of the systems given is p redominantly related to the different thermodynamic stabilities of alu minium and gallium chlorides in the vapour phase.