Investigation of the interface roughness of GaAs single quantum wells by X-ray diffractometry, reflectivity and diffuse scattering

The authors investigate thin GaAs single quantum wells with barriers consisting of AlAs / GaAs short-period superlattices by X-ray diffraction, reflection and diffuse scattering and by atomic force microscopy. The samples are grown by molecular beam epitaxy under different growth conditions on almost exactly oriented (001) GaAs wafers. Comparison of the experimental results from X-ray diffraction and reflectivity measurements with simulations yields the average thickness of both the superlattice layers and the single quantum well as well as the root mean square of the interface roughness. The high quality of the samples allows to determine the quantum well thickness from the interference fringes near the first-order satellite reflections of the diffraction curves. The analysis of the diffuse scattering shows different components; first the roughness, which is correlated over a large number of interfaces, and second a component with shorter lateral correlation length and reduced vertical correlation. The amount of diffuse scattering reflects the growth modes, i.e. step flow or two-dimensional nucleation. Comparison with simulations in the distorted-wave Born approximation yields different roughness exponents and lateral correlation lengths for the two respective growth modes. These values agree with the real space images of the surface roughness obtained by atomic force microscopy