A 90° double-reflection high-energy electron diffraction method was used to carry out a study of the morphology of vicinal (001) surfaces during molecular beam epitaxy. The technique permitted the simultaneous recording of reflection high-energy electron diffraction intensifies in the [¯110] and [110] azimuths. Comparative measurements of surfaces with 2° misorientations towards (111)Ga (A surface) or (1¯11)As (B surface) showed that, regardless of the step-type and reconstruction anisotropy, recordings of the specular beam intensity in the azimuth perpendicular to the steps were dominated by changes in the staircase order whereas intensity recordings in the azimuth parallel to the steps revealed changes in the step-edge roughness. Measurements which were performed over a wide range of substrate temperatures clarified the competition between kinetic processes and thermodynamic equilibrium. In the case of the A surface, the transition between 2-dimensional growth and step-flow growth not only occurred at a higher temperature than it did on the B surface, but the disappearance of intensity oscillations also occurred at differing substrate temperatures for different azimuths. An approximately 20C higher disappearance temperature for the [¯110] azimuth was explained in terms of previous scanning tunnelling microscopy results which had revealed an increasing elongation of islands, in the [¯110] direction, with increasing substrate temperature. The B surface was more isotropic, and therefore no difference in the transition temperature for the 2 azimuths could be detected. During growth in the transition range between 2-dimensional and step-flow growth, increased terrace-width fluctuations were observed on the B surface whereas the A surface became more uniformly stepped. It was concluded that, in the kinetically controlled regime, the anisotropic barrier height for downward diffusion of adatoms over step edges played an important role in the evolution of surface morphology. At high temperatures, the barrier height permitted downward jumps of the adatoms over B-type steps but not over A-type steps. Under conditions that were close to thermodynamic equilibrium, kinetic smoothing was observed on the A surface as well as on the B surface. This indicated that another mechanism became operative upon a change in the energetics due to ordering of the steps and disordering of the reconstruction on the terraces. This surface was metastable and rapidly recovered (within less than 1s) to give the equilibrium bunched surface after interruptions in growth at substrate temperatures above 580C.

H.Nörenberg, L.Däweritz, P.Schützendübe, K.Ploog: Journal of Applied Physics, 1997, 81[6], 2611-20