Scanning Tunnelling Microscopy Study of the Growth of 1-4 ML of Fe on GaAs(100)-2Ã\x976

One to four monolayer (ML) thick Fe films grown by MBE on GaAs(100)-2times6 using scanning tunnelling microscopy was examined. Magnetic measurements have been made on the ferromagnetic 4 ML film by MOKE and BLS. It has been shown previously that in the submonolayer regime Fe prefers to nucleate islands on top of As dimer rows of the 2times6 reconstruction. We show that for thicknesses greater than 1 ML these Fe islands only grow slowly along the [011] direction (perpendicular to the As dimer rows) but undergo drastic changes along the [0-11] direction, for the whole thickness regime studied, with a few islands clearly spreading across two As dimer rows. In the same thickness regime there is a clear peak in the island size along the [0-11] direction between 2 and 3 ML. We believe that this is indicative of structural percolation having occurred preferentially along this direction, and so we are seeing the pyramidal growth characteristic of Fe on Fe growth. The value of 2-3 ML is consistent with the previous publications, although we point out that the clusters are not large enough to support room temperature ferromagnetism until 3.8 ML of Fe have been grown.