The effect of substrate doping (InP:Sn and InP:Fe) and surface morphology of InP (001), misoriented 0.2 degrees off towards [110], on densities and sizes of self-assembled InAs quantum dots was investigated. The dots were deposited on either well-defined terraced surfaces with monolayer high steps,grown at 650 degrees C in the step-flow growth mode, or on more rough InP surfaces prepared at a lower temperature of 500 degrees C. The dot densities were found to vary between 0.5 x 10(10) cm(-2) < rho < 4.0 X 10(10) cm(-2) with otherwise identical growth conditions. The dot densities were lower on terraced surfaces and on Sn-doped substrates in comparison to the rougher surface and on Fe-doped substrates. This very broad scattering of densities indicates that InAs island formation on InP substrates is very sensitive to the choice of substrates and substrate preparation.