Growth and dissolution of ternary alloys of III-V compounds by liquid phase epitaxy and the formation of heterostructures

Abstract

In the LPE process, in contrast to other epitaxial processes, solid and fluid phases are close to equilibrium at their interface. Thus the underlying material (either the substrate or the last formed layer) can interact with the solution and hence can actively participate in the formation of the current layer. This is particularly true of multicomponent III-V systems, where each successive layer is formed from the same elements, albeit in different proportions. We review a model based on a minimum set of assumptions, we solve the appropriate transport equations, and we discuss this model in the light of recent experiments. Our conclusions include: (i) The computation of diffusion profiles is closely coupled to that of interface motion. (ii) When the solid tends to dissolve, the heteroepitaxial layer forms by solid state diffusion of material exchanged between liquid and solid through the moving interface. (iii) Compositional profiles in the solid depend crucially on departures from an exactly saturated condition in the liquid. (ic) For small enough solid diffusivities and liquid undercoolings, the LPE system behaves as if it were in a state close to equilibrium. (v) Diffusion coefficients in the solid are larger during dissolution than during growth. This is probably due to defect injection. (vi) There is no reason, experimental or theoretical, to believe that the average growth rate can ever change sign during a processing step, unless the system is subjected to temperature programming. © 1981.