Growth of GaxIn1-xAsyP1-y on (001) InP by molecular beam epitaxy employing solid phosphorus and arsenic sources supplied via valved cracking cells was investigated. For growth temperatures between 430-525 degrees C, the incorporation of As and P was found to be strongly dependent upon the Ga mole fraction, substrate temperature, and incident As and P fluxes. The relative incorporation of As and P is nonlinearly related to the incident column V fluxes, with P incorporation being enhanced with increasingly higher growth temperatures. The data show that the quaternary could be grown lattice matched to InP across the entire wavelength range 1.15-1.65 mu m, with strong photoluminescence emission. Heterojunction laser diodes subsequently fabricated with a broad range of emission wavelengths had threshold current densities as low as 1.7 kA/cm(2) with differential quantum efficiencies as high as 28%.