We have grown ErP on Ga0.52In0.48P (001) lattice-matched to GaAs and on InP (001) by low-pressure organometallic vapor phase epitaxy and investigated the surface morphology of ErP layers. Lattice-mismatch in ErP/Ga0.52In0.49P/GaAs heterostructures (Delta a/a = -0.8%) is much less than that of ErP/lnP heterostructures (-4.5%). Extended X-ray absorption fine structure measurement revealed that Er exists in the form of ErP rock-salt structure in both samples. The estimated growth rate of ErP on Ga0.52In0.48P is 1.8 ML/h. Our results demonstrate that ErP on Ga0.52In0.48P has smaller surface roughness than ErP on InP. Moreover, an ErP layer exists underneath the surface about 2 ML and the surface roughness does not depend on the ErP thickness in the range of our experiments (2.2-13.7 ML). (c) 2005 Elsevier B.V. All rights reserved.