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.

Deep levels in metamorphic InAs/In x Ga 1−x As quantum dot (QD) structures are studied with deep level thermally stimulated conductivity (TSC), photoconductivity (PC) and photoluminescence (PL) spectroscopy and compared with data from pseudomorphic InGaAs/ GaAs QDs investigated previously by the same techniques. We have found that for a low content of indium (x=0.15) the trap density in the plane of self-assembled QDs is comparable or less than the one for InGaAs/GaAs QDs. However, the trap density increases with x, resulting in a rise of the defect photoresponse in PC and TSC spectra as well as a reduction of the QD PL intensity. The activation energies of the deep levels and some traps correspond to known defect complexes EL2, EL6, EL7, EL9, and EL10 inherent in GaAs, and three traps are attributed to the extended defects, located in InGaAs embedding layers. The rest of them have been found as concentrated mainly close to QDs, as their density in the deeper InGaAs buffers is much lower. This an important result for the development of light-emitting and light-sensitive devices based on metamorphic InAs QDs, as it is a strong indication that the defect density is not higher than in pseudomorphic InAs QDs.

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 8 cm −2 dot density and metamorphic In x Ga 1−x As ͑x = 0.15, 0.30͒ confining layers result in emission wavelengths at 1.3 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.

Optical and photoelectric properties of metamorphic InAs/InGaAs and conventional pseudomorphic InAs/GaAs quantum dot (QD) structures were studied. We used two different electrical contact configurations that allowed us to have the current flow (i) only through QDs and embedding layers and (ii) through all the structure, including the GaAs substrate (wafer). Different optical transitions between states of QDs, wetting layers, GaAs or InGaAs buffers, and defect-related centers were studied by means of photovoltage (PV), photoconductivity (PC), photoluminescence (PL), and absorption spectroscopies. It was shown that the use of the InGaAs buffer spectrally shifted the maximum of the QD PL band to 1.3 μm (telecommunication range) without a decrease in the yield. Photosensitivity for the metamorphic QDs was found to be higher than that in GaAs buffer while the photoresponses for both metamorphic and pseudomorphic buffer layers were similar. The mechanisms of PV and PC were discussed for both structures. The dissimilarities in properties of the studied structures are explained in terms of the different design. A critical influence of the defects on the photoelectrical properties of both structures was observed in the spectral range from 0.68 to 1.0 eV for contact configuration (ii), i.e., in the case of electrically active GaAs wafer. No effect of such defects on the photoelectric spectra was found for configuration (i), when the structures were contacted to the top and bottom buffers; only a 0.83 eV feature was observed in the photocurrent spectrum of pseudomorphic structure and interpreted to be related to defects close to InAs/GaAs QDs.

No abstract

The physical properties of materials critically depend on the interatomic distances of the constituent atoms, which in turn can be tuned by introducing elastic strain (stress). While about four decades ago strain was generally regarded as a feature to be avoided in semiconductors, [1] strain engineering is nowadays ubiquitously used, e.g., to enhance the carrier mobility in transistors [2][3] and to achieve lasing action at reduced current densities in heterostructure lasers. [4] For this reason, its potential impact on our society has been compared to that of chemical alloying. [5] Strain can be used not only to enhance specific material/device properties, but also to impart completely new properties to a given material, thus opening the way to previously inaccessible applications. Examples are Ge turning into a direct-bandgap semiconductor suitable for lasers, [6][7][8][9] exciton dynamics tailoring in nanowires induced by strain gradients, [10] graphene electronic states engineering and strain-induced giant pseudomagnetic fields up to 300 T, [11][12] a topological insulator turning into a semiconductor, [13]

We report on a photoluminescence and photoreflectance study of metamorphic InAs/InGaAs quantum dot strain-engineered structures with and without additional InAlAs barriers intended to limit the carrier escape from the embedded quantum dots. From: (1) the substantial correspondence of the activation energies for thermal quenching of photoluminescence and the differences between wetting layer and quantum dot transition energies and (2) the unique capability of photoreflectance of assessing the confined nature of the escape states, we confidently identify the wetting layer states as the final ones of the process of carrier thermal escape from quantum dots, which is responsible for the photoluminescence quenching. Consistently, by studying structures with additional InAlAs barriers, we show that a significant reduction of the photoluminescence quenching can be obtained by the increase of the energy separation between wetting layers and quantum dot states that results from the insertion of enhanced barriers. These results provide useful indications on the light emission quenching in metamorphic quantum dot strain-engineered structures; such indications allow us to obtain light emission at room temperature in the 1.55 microm range and beyond by quantum dot nanostructures grown on GaAs substrates.

No abstract