The reduction of the dislocation density in relaxed SiGe/Si heterostructures using a low-temperature Si͑LT-Si͒ buffer has been investigated. We have shown that a 0.1 m LT-Si buffer reduces the threading dislocation density in mismatched Si 0.85 Ge 0.15 /Si epitaxial layers as low as ϳ10 4 cm Ϫ2. Samples were grown by both gas-source molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition.
We report growth of self-organized In 0.4 Ga 0.6 As quantum dots on Si substrates by molecular-beam epitaxy. Low-temperature ͑17 K͒ photoluminescence spectra show that the optical properties of In 0.4 Ga 0.6 As quantum dots grown on Si are comparable to quantum dots grown on GaAs substrates. We also present preliminary characteristics of In 0.4 Ga 0.6 As quantum-dot lasers grown on Si substrates. Light versus current measurements at 80 K under pulsed bias conditions show that I th ϭ3.85 kA/cm 2. The lasing spectral output has a peak emission wavelength of 1.013 m and a linewidth ͑full width at half maximum͒ of ϳ4 Å at the threshold.
Articles you may be interested inModeling room-temperature lasing spectra of 1.3-μm self-assembled InAs ∕ GaAs quantum-dot lasers: Homogeneous broadening of optical gain under current injection Tuning InAs/GaAs quantum dot properties under Stranski-Krastanov growth mode for 1.3 μm applications J. Appl. Phys. 91, 6710 (2002); 10.1063/1.1476069Room-temperature 1.3 μm emission from InAs quantum dots grown by metal organic chemical vapor deposition Quantum dots were grown by molecular beam epitaxy on GaAs substrates using a cycled submonolayer InAs/GaAs deposition technique. Their structural and luminescence characteristics have been compared with conventional self-organized dots. The room-temperature luminescence spectra are characterized by a ground state transition at 1.3 m and additional transitions corresponding to excited states. Cross-sectional transmission electron microscopy indicates that no dislocations are formed if the total InAs thickness is less than 5-6 monolayers. Temperature dependence of the photoluminescence indicates that both types of quantum dots may have nonradiative defects, caused by segregation and related phenomena.
The characteristics of ground and excited state luminescent transitions in In 0.4 Ga 0.6 As/GaAs and In 0.35 Ga 0.65 As/GaAs self-organized single-and multiple-layer quantum dots forming the active regions of lasers have been studied as a function of incident excitation intensity, temperature and number of dot layers. The results have been correlated with molecular beam epitaxial growth conditions. The threshold excitation density for the saturation of the ground state increases with the number of dot layers and no saturation is observed in samples with more than six dot layers up to an excitation power density of 2 kW/cm 2. The luminescent decay times for the ground and excited states are around 700 and 250 ps, respectively, almost independent of the number of dot layers.
Thermally stimulated current in self-organized InAs quantum dots Appl. Phys. Lett. 85, 5604 (2004); 10.1063/1.1832760Self-organized type-II In 0.55 Al 0.45 As/Al 0.50 Ga 0.50 As quantum dots realized on GaAs (311)A High density InAs and In 0.4 Ga 0.6 As dots were grown by molecular beam epitaxy on buried In 0.4 Al 0.6 As and In 0.4 Ga 0.3 Al 0.3 As stressor dots, respectively. Selective radiative recombination was achieved by engineering the band gap of the dots. Structural and luminescence measurements reveal increased size uniformity in the active region dots along with an increase in the dot density. A narrow photoluminescence linewidth of 19 meV was measured at Tϭ17 K.
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