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5 After the InAs deposition at 500°C, the substrate
temperature was kept at 500°C for 30 sec before
cooling to 100°C and removing the sample from the
growth chamber for atomic force microscopy imaging.
During the InAs deposition, the RHEED pattern
changes from streaky to spotty due to the transition
from 2D to 3D growth mode. By recording the inten-
sity of a Bragg spot along the [110] azimuth, we
measured the onset of the transition and the rate of
growth of the islands during the deposition of 3 MLs
of InAs (Fig. 1). The 3D growth onset occurred for
1.7 ML of InAs grown directly on GaAs, and the
intensity of the Bragg spots increased rapidly (about
0.3 ML) before saturating. We measured a 3D growth
onset for only 0.6 ML for InAs grown on PM-InAlAs
layer and the intensity increased during the following
0.8 ML prior to saturate. For the MM-InAlAs layer,
the Bragg spot intensity increased after the deposi-
tion of 1 ML and reached a maximum for additional
0.9 ML. These results indicate that the rates for the
growth of InAs islands on MM and PM-InAlAs layers
are similar and significantly slower than for the
growth of islands on GaAs layers.