Al diffusivity as a function of growth rate during the formation of (GaAl)As heterojunctions by liquid phase epitaxy

We have analyzed the heterojunctions formed on different parts of a wafer of GaAs which was exposed to a Ga-Al-As solution in the presence of a small temperature gradient. The effect of the temperature gradient was to cause growth over part of the wafer and dissolution over the remainder. Analysis of the profiles has demonstrated the diffusion coefficient of Al in the solid to be strongly dependent upon whether growth or dissolution is occuring. This result may explain an earlier discrepancy between measurements of the diffusion coefficient, which were made under different conditions. It also suggests reasons for the observed morphological instability during dissolution in such systems.