The growth and laser properties of In1-xGaxP1-zAsz/ GaAs1-yPysingle heterojunction laser diodes are described. High-quality p-type In1-xGaxP1-zAszlayers are grown by liquid phase epitaxy (LPE) on n-type VPE GaAs1-yPysubstrates of composition . Laser operation (77 K) of these quaternary-ternary heterojunctions is demonstrated at shorter wavelengths (<6300 Å) and lower thresholds ( A/cm2) than comparable GaAs1-yPyhomojunctions. The increase observed in threshold current ( ) between and GaAs1-yPysubstrates is attributed to the usual effect of EXapproaching near the direct-indirect transition. From the well-defined cavity mode structure observed on these hetero-junctions, data are obtained at relatively high energy on the index dispersion quantity , which increases monotonically with photon energy and provides a reference for the distinctly different behavior observed on N-doped GaAs1-yPy .