X-ray diffraction study of lattice strain relaxation in mismatched III-V heteroepitaxial layers

Lattice strain relaxation has been experimentally investigated in mismatched Ill-V heteroepitaxial layers by X-ray diffraction. Both binary (GaAs/lnP, GaAs/GaP, InP/GaAs) and temary (In1-xGa1-xAs/GaAs) layers have been studied. For the binary layers it has been found that the relaxation process is well described by the equilibrium theory, which assumes that a minimum energy state is achieved. However, the critical thickness for initiating the relaxation is usually larger than theoretically predicted. This is due to the fact that in real cases the initial growth usually occurs through island formation and this produces a relaxation smaller than expected in layer-by-layer growth. As for the ternary layers, two different behaviours have been observed. For high mismatch values, results similar to those obtained in the binary layers have been found. On the contrary, for lower mismatches the measured residual strains are much larger than predicted by the equilibrium theory and the relaxation process may be described by assuming that the elastic energy per unit interface area remains constant.