The use of surfactants in semiconductors during organometallic vapor phase epitaxy (OMVPE) is a powerful and exciting tool for controlling the properties of epilayers. The effects of the isoelectronic surfactants Sb and Bi have been systematically studied for GaInP alloys grown lattice-matched to GaAs substrates by OMVPE. Addition of small concentrations of either Sb or Bi leads to the elimination of the CuPt-B ordering observed in undoped layers, At high Sb concentrations, additional changes in the structure and optical properties are observed. The layers spontaneously form a structure with a lateral compositional modulation in the [I 10] direction. Surface undulations are clearly seen by atomic force microscopy (AFM) for the layers with compositional modulation. The low temperature photoluminescence (PL) peak energy is observed to decrease with increasing compositional modulation. The PL emission is strongly anisotropic, with a high intensity in the [I 10] direction which is the reverse of the polarization observed for CuPt ordered GaInP layers. Compositional modulation and surface undulation are found to be strongly affected by the growth rate. The amplitude of the compositional modulation in GaInP layers grown with either surfactant is significantly increased for decreased growth rates. The process controlling the amplitude appears to be kinetically limited. It is likely that adding the surfactant Sb or Bi increases the ad-atom surface diffusion coefficients which acts to enhance the extent of compositional modulation in GaInP especially when grown at low rates.