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This work systematically investigates the influence of InAs growth conditions and superlattice parameters on the optical properties of InAs/GaAs quantum dot (QD) superlattice structures grown by molecular beam epitaxy. Using surface photovoltage spectroscopy, one directly obtains the absorption spectra up to the highest confined QD levels at room temperature. Based on photoluminescence measurements at different excitation wavelengths, a feature below the fundamental transition is attributed to the transition from uncoupled dots in the bottom layers. The QD transition energy shift was found to be correlated with material intermixing, driven by enhanced strain strength with the increase of layer number and the decrease of spacer thickness, and the growth rate of InAs. A blueshift observed in low growth rate samples is indicative of greatly enhanced intermixing. For QD superlattices grown at a relatively high deposition rate of InAs, the material intermixing effect is gradually enhanced with increasing layer numbers, which will compensate the electronically coupled effect and will prevent further energy shift toward the lower energy side. The absorption wavelengths in 10- and 30-period InAs/GaAs QD superlattices with higher growth rates are near 1.32 μm. The results suggest that these QD superlattice structures can be used as promising active media for long-wavelength QD lasers operating at room temperature. [ABSTRACT FROM AUTHOR]

We report the effects of In[SUB0.33]Ga[SUB0.67]As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3 × 10[SUP10] to 1.7 × 10[SUP11]cm[SUP-2]. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm[SUP2]. A ground-state saturation gain of 16.6 cm[SUP-1] is achieved due to the high dot density. [ABSTRACT FROM AUTHOR]

The authors have used cross-sectional scanning tunneling microscopy to examine strain relaxation profiles of InAs quantum dots with In0.33Ga0.67As layers overgrown by three distinct capping methods. A statistical analysis of strain relaxation profile allowed them to infer that the long wavelength emission (>1.3 μm) of InAs quantum dots capped with sequential GaAs/InAs binary growth is mainly due to a weaker quantum confinement effect. This particular capping method is better than the traditional molecular beam epitaxy with simultaneous In/Ga/As deposition, and much better than a capping method with separated Ga deposition followed by As and InAs growth. [ABSTRACT FROM AUTHOR]

Temperature dependent photoreflectance (PR) and photoluminescence experiments of the InAs/GaAs quantum dot (QD) structures were performed. At 20 K, effective band-gap transitions due to the InAs QDs, wetting layers, and GaAs buffer and cap layers were identified. Transition energies of the ground state and four excited states with nearly equal interlevel spacings (75–80 meV) were observed. The linewidth of the ground-state transition decreased as the temperature increased from 20 K to 100 K while the linewidth became broader at temperatures above 100 K. Energy features of the PR spectra originating from QDs and relating to the in-plane parabolic potentials were discussed. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]