Structure and optical properties of GaInP epilayer with the ultrathin interfacial layers grown on germanium by metal-organic vapor-phase epitaxy (MOVPE) were characterized by high resolution transmission electron microscopy (HRTEM), photoluminescence (PL), Raman as well as surface morphology measurement. A five angstroms (5 A) AlAs interfacial layer results in the decrease of PL intensity arising from the emission of [Ge-(Ga,Ge-In) - V-(Ga,V-In)]complex. With the incorporation of AlAs interfacial layer, an increased ordered degree of GaInP epilayer is observed. On the basis of the combination of step-terrace-reconstruction (STR) mode with the dimer-induced-stress model, a CuPt-B type ordering of GaInP which is related to AlAs reconstruction with 2x periodicity process is proposed to explain this effect. Long range order occurs as a consequence of the minimization of the strain energy with increased interfacial layer thickness from 5 A to 5 nm. (C) 2014 Elsevier B.V. All rights reserved.