Metamorphic quantum dots: Quite different nanostructures

Abstract

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates Appl. Phys. Lett. 98, 173112 (2011); 10.1063/1.3584132 In islands and their conversion to InAs quantum dots on GaAs (100): Structural and optical properties J. Appl. Phys. 107, 014312 (2010); 10.1063/1.3269700 1.59 μ m room temperature emission from metamorphic In As ∕ In Ga As quantum dots grown on GaAs substrates Appl.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.

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

“…Moreover, the emission efficiency of single QDs grown on In 0.30 Ga 0.70 As LCLs is 20% of the one from QDs grown on In 0.15 Ga 0.85 As LCLs. The lower optical quality of the emission in the x = 0.30 sample and the larger PL linewidth in the present case could be explained by the role of the high indium content in the metamorphic layer, leading to an higher plastic relaxation of the strain and an higher density of structural defects 10 and broadening of the PL peaks can be related to a spectral diffusion effect by impurities or structural defects. 28,29 Nevertheless there are many methods that can be used to consistently reduce the density of defects close to QDs in metamorphic nanostructures, such as the use of InGaAs graded buffers, 30 of QD layers acting as defect filters 31 and of an ad hoc defect reduction technique.…”

“…12 Here we report on an original approach to obtain single QD emission from metamorphic structures, relying on subcritical InAs coverages deposited on relaxed InGaAs layers, that allows to obtain 10 8 cm −2 QD density, homogenously distributed on the surface. As discussed in some works, 10,12 growing QDs on metamorphic InGaAs is different from growing them on GaAs, due to the reduced mismatch between QDs and lower confining layer ͑LCL͒ and the dissimilar surface. Thus, the aim of the letter is the study of single QD emission and of peculiarities of this system in comparison with the InAs/GaAs one.…”

“…6,17 These experimental results could be explained by modified kinetics of adatoms due to different composition, strain fields, and morphology of the surface, strengthening the notion that InAs QD deposition on InGaAs surfaces is intrinsically different from growth on GaAs ones. 10,[18][19][20] Figures 2 and 3 show PL from samples with x = 0.15 and x = 0.30 LCLs, respectively, under different power excitations. At low excitation power both spectra show localized narrow lines characteristic of single QD emission.…”

“…4,5,8 To extend the emission up to 1.55 m, the growth of QDs on metamorphic buffers has been useful for high density structures. [9][10][11] This approach has been also considered for low density QDs; the substrate rotation is stopped during InAs deposition but single QD emission is observed only in a restricted area. 12 Here we report on an original approach to obtain single QD emission from metamorphic structures, relying on subcritical InAs coverages deposited on relaxed InGaAs layers, that allows to obtain 10 8 cm −2 QD density, homogenously distributed on the surface.…”

Time resolved emission at 1.3 μm of a single InAs quantum dot by using a tunable fibre Bragg grating

“…In our case we have found + / = 1,2. InAs bulk Bohr radius (aB) is 25 nm, and in these samples with In0.15Ga0.85As metamorphic layers the diameter of QD (dQD) can be estimated to be in the 30-45 nm range [18], which is larger than the sizes of metamorphic QDs grown with the SK method [33], [34]. The ratio dQD/aB > 1 justifies the weak quantum confinement limit, where a deviation from the strong confinement time decay relation ( + / = 2) is hence expected.…”