In0.53Ga0.47As layers were grown by LPE on (001) InP substrates in the temperature range of 480~780°C. The fine speckle contrast, which is attributed to two-dimensional phase separation, was observed in layers grown at temperatures as high as 780°C. Since the critical temperature for bulk miscibility gap is predicted to be around 450°C, this suggests that in the presence of the surface the critical temperature for the two-dimensional surface decomposition is higher than that for the bulk. The wavelength of the fine modulations does not change with the growth temperature. This could be due to the fast diffusion kinetics in the solid-liquid interface and the balance between the driving force and the gradient energy.
To examine the stability of the above microstructures, zinc diffusion experiments were carried out in the temperature range of 390 to 540°C using the ampoule technique. The diffused layers exhibit homogenous microstructures. This demonstrates that critical temperature for phase separation in bulk is below 390°C and is comparable to that predicted by theory.