GaInAsP epilayers grown on GaAs substrate by solid source molecular beam epitaxy with a valve phosphorous cracker cell at varied arsenic beam equivalent pressure ratio, f(As)/(f(As)+f(P)), were investigated. It is found that the InGaAsP/GaAs can be easily grown with the solid sources, and the incorporation rate of arsenic is higher than that of phosphorous and varies with arsenic to phosphorous beam equivalent pressure (BEP) ratio, f(As)/(f(As)+f(P)). The lattice mismatch, Delta a/a(s), varies from negative to positive linearly with BEP ratio and follows a polynomial expression with arsenic composition. GaP-, InP-, GaAs-, and InAs-like LO modes are observed in all samples and shift as expected. The GaP- and InP-like TO mode is observed in most of the samples while the GaAs-like TO mode is observed only in the sample with an arsenic composition of 0.96. Photoluminescence measurements reveal that the luminescence peak energy of the materials does nut change significantly at high arsenic composition but increases drastically with the decrease of arsenic composition. The full width at half maximum is found to be the largest in the sample with peak energy of 1.75 eV due likely to cluster formation. All samples studied show smooth surfaces.