Growth-induced interface roughness of GaAs/AlAs-layers studied by X-ray scattering under grazing angles

We have studied GaAs/AlGaAs- and GaAs/AlAs-samples grown by molecular beam epitaxy by X-ray scattering under grazing angles to investigate surface and interface roughness. We discuss the reliability of buried interface roughnesses derived from fits to specular reflectivity by means of a sample series grown at substrate temperatures from 605 to 685 degrees C, Even for samples of high perfection no abrupt interfaces were found. We have applied this method to the problem of growth-induced roughening of GaAs- and AlAs-layers. Sample series with increasing film thickness between 50 and 2000 Angstrom for AlAs and 5000 Angstrom for GaAs have been investigated. We observe roughening which in the case of AlAs does not follow a power law expected within the framework of kinetic roughening theory. However, for GaAs the data can be described by a very small growth exponent beta = 0.11 +/- 0.03.