Does scanning tunnelling microscopy provide a realistic picture of the step 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 morphology of vicinal GaAs(001) surfaces during molecular beam epitaxy, in particular at high temperatures where the quenching for scanning tunnelling microscopy studies (STM) is a problem. In the transition range between 2D and step flow growth the terrace width fluctuation is found to increase on the B-surface (2 degrees misorientation towards (1<(1)over bar 1>)As), whereas the A-surface (2 degrees misorientation towards (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 temperatures between 2D and step flow growth are found in the [<(1)over bar 10>] and [110] azimuths. In accordance with STM results this is explained by an increasing elongation of islands in [<(1)over bar 10>] direction with increased substrate temperature. Above 580 degrees C kinetically smoothed A and B surfaces transform after growth interruption rapidly to less ordered equilibrium surfaces. On the A-surface in addition the adatom concentration changes rapidly. Both processes occur in less than 1 s which creates problems to properly quench such surfaces for STM studies.