Epilayer thickness influence on composition modulation of low temperature grown InGaAs/GaAs(001) layers

Abstract

We have developed a Transmission Electron Microscopy study of In0.2Ga0.8As layers grown on GaAs (001) substrates by Atomic Layer Molecular Beam Epitaxy at 200 °C. Our results show that the apparition of composition modulation in these samples depends on the layer thickness, the thinnest being homogeneous. Therefore, the phase separation in these low temperature grown systems should have occurred in bulk on arriving to a critical layer thickness between 80 nm and 300 nm and not at the surface during growth as it has been widely reported. Accumulated elastic energy due to an increasing epilayer thickness seems to be a crucial factor in this critical thickness. On the other hand, we have observed a high asymmetry in the contrast modulation wavelength for these low temperature grown samples for the [110] and [1 10] directions, contrary to the symmetrical ones found in structures grown by conventional MBE at 500 °C.