The effect of water and ozone as the oxidant in the atomic layer deposition (ALD) of aluminum oxide on the ammonium-sulfide-passivated In0.53Ga0.47As surface is compared using X-ray photoelectron spectroscopy (XPS) after each "half-cycle" of the ALD process. While the first half-cycle of the aluminum precursor tri-methyl aluminum (TMA) reduces the residual native oxides to within detection limits of XPS, the ozone oxidation process causes significant reoxidation of the substrate in comparison to the water-based process. Subsequent TMA pulses fail to remove the excess interfacial oxides caused by ozone oxidation, resulting in the formation of an oxide interlayer.