Engineering topics

Seravalli, L

Publications and source records attributed to Seravalli, L.

3 records

DOE OSTI2011

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 10{sup 8} cm{sup -2} dot density and metamorphic In{sub x}Ga{sub 1-x}As (x=0.15,0.30) confining layers result in emission wavelengths at 1.3 {mu}m. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2011

Raman scattering in InAs/AlGaAs quantum dot nanostructures

We report on Raman scattering experiments on InAs/Al{sub x}Ga{sub 1-x}As quantum dot heterostructures with 0{<=}x{<=}0.6. The samples were prepared by using molecular beam epitaxy (MBE) and atomic layer MBE for the growth of different layers. For x>0, we detected several lines originating from the Al{sub x}Ga{sub 1-x}As alloy. These can be related to scattering from GaAs-like and AlAs-like phonons with q congruent with 0, and weaker scattering from disorder-activated phonons with q{ne}0. In particular, we identified a line at {approx}250 cm{sup -1} as due to disorder-activated longitudinal optical phonons in the alloy. This conclusion is different than the attribution of this line to scattering from dots and, consequently, we do not recognize the possibility of deriving any information about the actual composition of the dots from an analysis of this line as proposed by other authors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2010

Metamorphic quantum dots: Quite different nanostructures

In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantum dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.

36 MATERIALS SCIENCE↗