Thermally Induced Relaxation in GaInNAsSb Quantum Well Structures
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Thermally Induced Relaxation in GaInNAsSb Quantum Well Structures Evan Pickett1, Seth Bank2, Homan Yuen1, Hopil Bae1, Tom·s Sarmiento1, Ann Marshall1, and James Harris1 1 Stanford University, Stanford, CA, 94305 2 The University of Texas at Austin, Austin, TX, 78712 Abstract GaInNAsSb quantum wells with GaNAs barriers, grown via molecular beam epitaxy (MBE) on 100-oriented GaAs substrates at varying temperatures, were analyzed using photoluminescence (PL), high-resolution x-ray diffraction (XRD), transmission electron microscopy (TEM), and energy-dispersive spectrometry (EDS). Samples grown at 420 ∞C, 440 ∞C, and 470 ∞C were analyzed, as were two pieces of the 440 ∞C growth temperature sample that had been annealed at 740 ∞C and 820 ∞C. These measurements showed that the decrease in PL with higher growth temperatures was due to the onset of 3D growth and the nucleation of dislocations. The degradation associated with overannealing was likely due to dislocation nucleation. The poor PL associated with low growth temperatures was due to another mechanism, most likely arsenic anti-site defects. EDS measurements showed greater composition uniformity with lower growth temperatures, as expected, and also showed that there was no ordered indium-rich or indium-poor phase separation at any temperature. Phase separation upon annealing was not observed. Introduction Since the discovery of the large negative band bowing parameter created by dilute amounts of nitrogen in GaAs [1], there has been a great deal of research into semiconductor alloys based on this material. By combining In and N in GaAs in a strained quantum well, it is possible to redshift the optical emission of the alloy below 800 meV or 1.55 µm, the loss minimum in silica fiber optic cable. Lasers based on the GaInNAs/GaAs system hold the promise of easier processing and better temperature stability than the currently commercially used InGaAsP/InP system. The alloy can also be grown latticed-matched to GaAs with a bandgap around 1.0 eV, enabling its use in high-efficiency, multi-junction solar cells [2]. Antimony is used as a surfactant during the growth of GaInNAs by MBE to improve the homogeneity of the material and to inhibit the transition to 3D growth [3]. Dilute amounts of antimony, inversely proportional to the indium content, are incorporated into the alloy [4]. The resulting alloy, GaInNAsSb, has been used to produce edge-emitting lasers with record-low threshold current densities [5], as well as vertical cavity surface-emitting lasers at 1.55 µm [6]. One of the most important factors affecting the structural and optical quality of the materials is the growth temperature [7]. Outside the optimal growth temperature of 440 ∞C, PL intensity drops off by an order of magnitude when a sample is grown 20 ∞C too hot or too cold. Likewise, annealing conditions ñ temperature and duration ñ have a strong effect on PL intensity [8], and a noticeable effect on crystal structure. These effects will be further explored in this paper. The experiments perform
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