DOES SCANNING-TUNNELING-MICROSCOPY PROVIDE A REALISTIC PICTURE OF THESTEP ARRAY OF VICINAL GAAS(001) SURFACES GROWN AT HIGH-TEMPERATURE

A 90 degrees double reflection high-energy electron diffraction (RHEED ) set-up was used to perform a two-dimensional (2D) study of the morph ology of vicinal GaAs(001) surfaces during molecular beam epitaxy, in particular at high temperatures where the quenching for scanning tunne lling microscopy studies (STM) is a problem. In the transition range b etween 2D and step flow growth the terrace width fluctuation is found to increase on the B-surface (2 degrees misorientation towards (1<(1)o ver bar 1>)As), whereas the A-surface (2 degrees misorientation toward s (111)Ga) becomes more uniformly stepped. This is discussed in terms of different barrier heights for downward diffusion of Ga adatoms over A-and B-type steps. For the A-surface different apparent transition t emperatures between 2D and step flow growth are found in the [<(1)over bar 10>] and [110] azimuths. In accordance with STM results this is e xplained by an increasing elongation of islands in [<(1)over bar 10>] direction with increased substrate temperature. Above 580 degrees C ki netically smoothed A and B surfaces transform after growth interruptio n rapidly to less ordered equilibrium surfaces. On the A-surface in ad dition the adatom concentration changes rapidly. Both processes occur in less than 1 s which creates problems to properly quench such surfac es for STM studies.