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Substantial defect reduction was achieved in InAs/GaAs by lateral epitaxial overgrowth in which InAs was grown on mask-patterned ͑100͒ GaAs with stripe-shaped windows of various widths by metalorganic chemical vapor deposition. The InAs growth morphology, crystal quality, and microstructure were evaluated using double-crystal x-ray rocking curves and scanning and transmission electron microscopy. The microstructure of the InAs grown on mask-free control samples was comprised of micron-scale misoriented grains and dislocations at a density of 10 11 cm Ϫ2 . As the width of the mask openings decreased to 0.8 m, the rocking curves narrowed, grain boundaries disappeared and the dislocation density decreased to Ͻ10 7 cm Ϫ2 . The distribution of the remaining defects suggests substantial changes in microstructural development when the window width is Շ1 m.

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Low temperature ͑30 K͒ long wavelength photoluminescence emission ͑ = 1400-1600 nm͒ from metalorganic chemical vapor deposition grown InGaAsN-GaAsSb type II "W" quantum wells ͑QWs͒, on GaAs substrates has been demonstrated. Thin layers ͑2-3 nm͒ and high antimony-content ͑30%͒ GaAsSb were utilized in this study for realizing satisfactory wave function overlap and long wavelength emission. Tensile strained GaAsP barriers effectively improve the material structural and luminescence properties of the compressive strained active region. Room temperature photoluminescence data show that the type-II QW design is a promising candidate for realizing long wavelength GaAs-based diode lasers beyond 1500 nm.