Photoluminescence (PL), contactless electroreflectance (CER), and Raman scattering measurements have been used to study the structural properties of Ho-doped InGaAsP epilayers. Both the full width at half maximum (FWHM) of PL and the broadening parameter of CER are decreased as the doping amount of Ho element increases. This indicates that Ho doping greatly reduces the residual impurities and improve the quality of epilayers. The Raman spectra of Ho-doped InGaAsP epilayers are found to have asymmetric line shapes. Using a spatial correlation model, it is found the asymmetric broadening of the Raman signal is not influenced by the Ho doping. We hence conclude that the introduction of the Ho element can greatly reduce the residual impurities of LPE-grown layers, but no large amounts of Ho element are being incorporated into the epilayers during the purification.