Self-assembled InAs and In0.5Ga0.5As islands fabricated on Ge and GaAs substrates by metal organic vapor phase epitaxy are investigated. The effects of growth temperature and deposition thickness on the formation, size, density, and uniformity of the islands are examined. Atomic force microscopy images show the formation of both InAs and InGaAs islands for submonolayer depositions on Ge. For the InAs islands grown at 450degreesC an island density of order similar to10(8) cm(-2) is observed when the deposition thickness is as low as 0.4 monolayer. For the InGaAs islands on Ge a maximum density is reached at a nominal three monolayers deposition thickness which is still observed to be below critical thickness for island formation on GaAs. (C) 2004 Elsevier B.V. All rights reserved.