We describe optical and structure characteristics of InAs quantum dashes grown on a GaAs substrate using an AlGaAsSb metamorphic buffer. The metamorphic buffer increases the lattice constant of the growth matrix from 5.653 to 5.869 Å. The increased lattice constant of the growth matrix yields a lattice mismatch with the InAs active region of only 3.2% and accommodates a large In content to access emission wavelengths >2.0 μm. From our comparison with quantum dot structures, we conclude that the elongated quantum dash formation is due to asymmetric surface bonds in the zinc blende crystal structure that control surface migration in low strain conditions.

We have introduced tensile layers embedded in a GaAs matrix to compensate compressive strain in stacked 1.3 m InAs quantum dot (QD) active regions. The effects of the strain compensation are systematically investigated in five-stack and ten-stack QD structures where we have inserted In x Ga 1−x P (x = 0.30 or 0.36) layers. High-resolution x-ray diffraction spectra quantify the overall strain in each sample and indicate Ͼ35% strain reduction can be accomplished. Both atomic force and transmission electron microscope images confirm that strain compensation improves material crystallinity and QD uniformity. With aggressive strain compensation, room temperature QD photoluminescence intensity is significantly increased demonstrating a reduced defect density.Quantum dot (QD) material has drawn considerable interest for more than ten years due to the optoelectronic advantages that zero-dimensional systems offer. Impressive properties such as low threshold current 1 and current density, 2 low chirp, 3 and high characteristic temperature 4 have been demonstrated. However, low gain at the ground state transition is often considered a limiting factor in the QD device performance. 5 Several groups have reported stacking the QD layers to increase modal gain near 1.3 m 6-8 resulting in ground-state lasing and larger T 0 . However, accumulated overall strain in the epitaxial material can cause defects and nonradiative recombination centers that increase the threshold current density 6 and cause device failure. A thick spacer ͑300-500 Å͒ between the QD layers is often used to reduce strain accumulation and defects. However, the extended active region reduces the optical overlap and is not attractive for microcavity lasers.The compensation of compressive strain by inserting tensile layers has been demonstrated using InGaP and InGaAsP in multiple strained quantum well lasers. Improvements in both crystalline quality and lasing performance including higher photoluminescence (PL) intensity, narrower PL linewidth, and lower threshold current density have been proven. 9-11 The use of strain compensation (SC) to reduce defect formation in stacked QD actives may be a powerful parameter in designing laser structures, but has not been well studied. This is likely due to the inconvenience of a pyrophoric phosphide source in QD-growing molecular beam epitaxy systems. Only recently, the use of tensile GaNAs cap layers 12,13 was reported to improve luminescence efficiency in In͑Ga͒As-based QDs.In this letter, we discuss the effects of InGaP SC layers on five-stack and ten-stack QD ensembles. Our samples are grown by metalorganic chemical vapor deposition (MOCVD) at 60 Torr using trimethylgallium ͑TMGa͒, trimethylindium ͑TMIn͒, tertiarybutylphoshine (TBP), and arsine ͑AsH 3 ͒. Growth is initiated on a GaAs͑001͒ substrate with a 3000 Å GaAs layer at 680°C, then the temperature is reduced and stabilized for active region growth within the range of 450-520°C. All active regions consist of a 5 monolayer (ML) In 0.15 Ga 0.85 As buffer layer, a 3 ML...

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