Scanning tunneling microscopy of flat and vicinal molecular-beam epitaxy grown GaAs(001)-(2×4) surfaces: The effect of growth rate

Abstract

Scanning tunneling microscopy (STM) has been used to investigate the effect of the deposition rate on the resulting morphology of nominally flat and vicinal GaAs(001)-(2×4) surfaces grown by molecular-beam epitaxy. On the nominally flat surfaces, low deposition rates are found to create smooth surfaces and lead to anisotropic islanding with an A-type step (Ga terminated, parallel to the [1̄10] direction) to B-type step (As terminated, parallel to the [110] direction) average aspect ratio which is larger than that produced by standard deposition rates. The results suggest that the increase in the island anisotropy at low growth rates reflects the energetics of the step edges. In contrast, the growth rates investigated are found not to have any obvious effect on the resultant morphology of the 2° A-type vicinal surfaces. In particular, no islanding on the terraces is observed at either deposition rate. However, detailed statistical analyses of the STM images indicate that there is a larger spread in the terrace width and a greater probability for forming kinks with increasing growth rate. This observation suggests that the probability of a Ga adatom incorporating at an A-type step (rather than at a B-type kink) is greater for standard growth rates than for low growth rates.