We report gas-source molecular-beam epitaxy of Ga1-xInxNyP1-y grown on GaAs(100) substrates. Nitrogen incorporation dramatically reduces the Ga1-xInxP band gap. With nitrogen incorporation, the photoluminescence (PL) peak energy exhibits an inverted S-shaped dependence with temperature, and the low-temperature PL spectra exhibit an asymmetric line shape with a low-energy tail. Both indicate the presence of N-related localized states, which dominate the radiative recombination processes at low temperature. N incorporation significantly reduces the free-electron concentration and mobility. The free-electron concentration of N-containing Ga0.48In0.52N0.005P0.995 decreases dramatically with high-temperature annealing (800 °C), from 4.4×1018 to 8.0×1016 cm-3. This is believed to be due to passivation of Si by N through the formation of Si–N pairs. © 2003 American Institute of Physics.