Properties Of InAs Quantum Dots Research Articles

In segregation influence on properties of InAs quantum dots in dots-in-a-well

We investigated the growth of InAs quantum dots (QDs) in a dots-in-a-well (DWELL) from the perspective of the influence of In segregation from the InGaAs layers in the DWELL. Reflection high-energy electron diffraction (RHEED) measurements during the growth of the lower InGaAs layer indicated that In segregation increased with the In composition of the InGaAs layer. The estimated In segregation values were consistent with the decreases in the critical thickness for the QDs growth and the total volume variations of the grown QDs. These results illustrate that the segregated In from the lower InGaAs layer contributes to the QD growth in the DWELL, and their density increases. Furthermore, RHEED measurements during the growth of the upper InGaAs layer indicated the suppression of the deformation of embedded QDs , which could partially contribute to the longer emission wavelength of the QDs in the DWELL.

Photoluminescence Properties of InAs Quantum Dots Overgrown by a Low-Temperature GaAs Layer under Different Arsenic Pressures

We studied the influence of the arsenic pressure during low-temperature GaAs overgrowth of InAs quantum dots on their optical properties. In the photoluminescence spectrum of quantum dots overgrown at a high arsenic pressure, we observed a single broad line corresponding to unimodal size distribution of quantum dots. Meanwhile, two distinct peaks (~1080 and ~1150 nm) at larger wavelengths are found in the spectra of samples with quantum dots overgrown at a low arsenic pressure. We attributed this phenomenon to the high-pressure suppression of atom diffusion between InAs islands at the overgrowth stage, which makes it possible to preserve the initial unimodal size distribution of quantum dots. The same overgrowth of quantum dots at the low arsenic pressure induces intensive mass transfer, which leads to the formation of arrays of quantum dots with larger sizes. Integrated photoluminescence intensity at 300 K is found to be lower for quantum dots overgrown at the higher arsenic pressure. However, a difference in the photoluminescence intensity for the high- and low-pressure overgrowths is not so significant for a temperature of 77 K. This indicates that excess arsenic incorporates into the capping layer at high arsenic pressures and creates numerous nonradiative recombination centers, diminishing the photoluminescence intensity.

Optical properties of self-assembled InAs quantum dots based P–I–N structures grown on GaAs and Si substrates by Molecular Beam Epitaxy

Extensive work on InAs quantum dots grown on GaAs substrates has been reported in the literature. However, research in the use of different substrate materials such as silicon to achieve an ideal and full integration of photonic and electronic systems is still a challenge. In this work we have investigated the effect of the substrate material (Si and GaAs) and strain reducing layer on the optical properties of InAs quantum dots for possible applications in laser devices grown by Molecular Beam Epitaxy. Two InAs quantum dots structures with similar active regions grown on GaAs and Si substrates using strain reducing layer consisting of InAs QDs/6 nm In0.15Ga0.85As have been investigated. Atomic Force Microscopy, Transmission Electron Microscopy, and photoluminescence have been used for the characterization of the samples. We have observed a red shift of the InAs QD photoluminescence peak energy for the sample grown on Si substrate as compared to the sample grown on GaAs substrate, which was associated with residual biaxial strain from the Si/GaAs heterointerface. This red-shift of the photoluminescence peak energy is accompanied by a broadening of the photoluminescence spectrum from ∼31 meV to a value of ∼46 meV. This broadening is attributed to the quantum dots size inhomogeneity increase for samples grown on Si substrate. This result open new insights for the controlling the emission of InAs quantum dots for photonic devices integration using Si substrates.

Structural, Optical and Electrical Properties of Self-Assembled InAs Quantum Dots Based p–i–n Devices Grown on GaAs Substrate by Molecular Beam Epitaxy for Telecommunication Applications

This work aims to investigate the structural, electrical, and optical properties of InAs quantum dots (QDs) grown by Molecular Beam Epitaxy on GaAs substrates. As-made samples were thoroughly characterized using different techniques, including Atomic Force Microscopy (AFM), X-ray diffraction (XRD), and highresolution X-ray diffraction (HRXRD). The patterns of HRXRD revealed an excellent crystallinity of the nanostructure with a maximum diameter of 25 nm as demonstrated by AFM images. The photoluminescence (PL) spectra showed two distinct bands centered at 835 and 1210 nm, and the intensity of these wavelengths increased with decreasing temperature. A redshift accompanied by a decrease in the FWHM as a function of temperature was observed as a consequence of the thermal escape of carriers. The Ideality factor (n), built-in potential energy, and series resistance at different temperatures were also determined from current-voltage characteristics curves.

Optical properties of InAs quantum dots embedded in InGaAs/AlGaAs/GaAs structures with different capping layers

The InAs quantum dots (QDs) embedded in Al0.30Ga0.70As/InGaAs/AlGaInAs/Al0.30Ga0.70As structures and covered by strain reduced AlGaInAs capping layer have been investigated in as grown state by means of a photoluminescence method. Three types of QD structures with different QD capping layers: GaAs (#1), Al0.10In0.15Ga0.75As (#2) and Al0.40In0.15Ga0.45As (#3) are compared. It is revealed that the QD emission in the structure with Al0.10In0.15Ga0.75As capping is characterized by the highest PL intensity of the ground state (GS) band and smaller the full with at half maximum (FWHM), compared to #1 and #3 structures. The variation of the GS emission peak versus temperature has been monitored within the range of 10-500K for the as grown film states and compared with shrinkage of the energy bandgaps in the InAs and GaAs bulk crystals. The results show that the efficiency of Ga/Al/In intermixing in #2 and #3 is less than in #1. Finally, the peculiarities of PL spectra of the studied QD structures have been analyzed and discussed.

GaAs/InGaAs heterostructure strain effects on self-assembly of InAs quantum dots

Abstract In this study, the quantum dots (QDs) self-assembly properties were affected by strain modulation. The strain of the GaAs (100) surface was modulated prior to the growth of InAs with the aim to tailor the size and distribution of self-assembled QDs. Changes in the strain fields were achieved with the buried GaAs/InGaAs heterostructure by varying the GaAs layer thickness Σ, which significantly influences several parameters collectively involved in the QDs self-assembly process. In situ characterization of the heterostructure shows that the InAs/GaAs critical thickness and the surface diffusion parameter, the latter of which is an indicative of the QDs density, decreased with Σ. High-resolution X-ray diffraction measurements confirmed that depending on Σ, the InGaAs layer can be partially relaxed, presumably through the introduction of dislocations that are advanced by the QDs strain. Numerical simulations of the heterostructures were performed, with the sample's geometry and other properties obtained from its experimental characterization as input data. The results confirmed variations in strain resulting from changes in the GaAs/InGaAs heterostructure. These findings contribute to the understanding of strain distribution and can thus lead to improvements in the self-assembly properties of InAs QDs.

Influence of the excitation density and temperature on the optical properties of type I InAs/GaAsSb quantum dots

In this study, the optical properties of InAs quantum dots (QDs) were characterized using photoluminescence (PL) measurements. The QDs, capped with GaAs and GaAs1−xSbx (x = 6%) strain-reducing layer (SRL), were grown by Molecular Beam Epitaxy. Temperature-dependent photoluminescence (TDPL) of both ground state (GS) and first excited state (ES) was carried out through the analysis of the PL peak position as well as the integrated PL intensity. The temperature dependence of the integrated PL intensity shows the carrier trapping in the potential barrier at the interface between the capping layer and QDs in both samples at low temperatures for the GS and ES. The Excitation density dependent photoluminescence (EDPL) showed a redshift of the GS and ES PL peak energies with increasing excitation density. We attribute this variation to the bandgap renormalization (BGR) effect. The potential barrier reduction for the GaAsSb-capped QDs increases carrier injection efficiency inside the QDs, giving rise to a larger BGR effect compared to the QDs capped with GaAs. With increasing temperature, BGR redshift varies considerably for the GaAs- capped QDs but less for the Q with GaAsSb SRL. This effect was explained using the population rate of carriers inside the QDs while taking into account the nonradiative recombination process for the two samples. Furthermore, the variation of the integrated intensity with the excitation power density grows superlinearly for the two samples for a temperature range from 10 K to 220 K. This behavior was explained by the random capture of carriers in the dots. The sample with GaAsSb SRL having a smaller potential barrier has reduced superlinear dependence at low temperatures. Losses mechanism has a significant impact on increasing the superlinear dependence at high temperatures. The ES showed a stronger superlinearity compared to the GS. This study helps to understand the optical mechanisms in some devices, such as QD lasers.

Study of nanometer-scale structures and electrostatic properties of InAs quantum dots decorating GaAs/AlAs core/shell nanowires

The configurations of core/shell nanowires (NWs) and quantum dots (QDs) decorating NWs have found great applications in forming optoelectronic devices thanks to their superior performances. The combination of the two configurations would expect to bring more benefits, however, the nanometer-scale electrostatic properties of the QD/buffer layer/NW heterostructures are still unrevealed. In this study, the InAs QDs decorating GaAs/AlAs core/shell NWs are systemically studied both experimentally and theoretically. The layered atomic structures, chemical information, and anisotropic strain conditions are characterized by comprehensive transmission electron microscopy (TEM) techniques. Quantitative electron holography analyses show a large number of electrons accumulating in the InAs QD, especially at the dot apex, and charges of reversed signs and similar densities are observed to distribute at the sequential interfaces, leaving great amounts of holes in the NW core. Theoretical calculations including simulated heterostructural band structures, interfacial charge transfer, and chemical bonding analysis are in good accordance with the experimental results, and prove the important role of the AlAs buffer layer in adjusting the heterostructural band structure as well as forming stable InAs QDs on the NW surfaces. These results could be significant for achieving related optoelectronic devices with better stability and higher efficiency.

The effect of nitridation on the optical properties of InAs quantum dots grown on GaAs substrate by MBE

InAs/GaAs quantum dots (QDs) under their exposure to a nitrogen plasma were investigated using photoluminescence (PL) and X-Ray Photoelectron Spectroscopy (XPS) techniques. The motivation of this work is to study the effect of nitrogen in InAs QDs, and their role in the amelioration of optical properties. At low temperature, nitrogen addition causes a red-shift of the PL emission. This can be explained by reduction of quantum confinement. Power-dependent analysis of PL exhibit that the transition is about band-to-band intrinsic recombination which may be due to the formation of a lnAsN thin layer at the interface of InAs QDs.XPS is used to determine the species created at the surface. To follow QDs nitridation, we focused our attention on the N1s and In3d XPS spectra.The temperature dependent PL measurements in the range 10–300 K for nitrided InAs QDs showed an S-shape in PL peak energy and contributed to an estimated value of exciton localization energy.In addition, by increasing the time nitridation in InAs QDs, the emission wavelength increases further. Our results displayed a significant improvement of the crystalline quality and enhancement of the optical properties for InAs QDs grown after nitridation.

Comparative study of photoluminescence for type-I InAs/GaAs0.89Sb0.11 and type-II InAs/GaAs0.85Sb0.15 quantum dots

InAs quantum dots (QDs) sandwiched inside a GaAsSb matrix possess advantages for achieving telecom wavelength lasers and for developing high efficiency solar cells. In this work, optical properties of InAs quantum dots (QDs) capped by GaAs1-xSbx (x = 0.11 and 0.15) are comparatively investigated. The photoluminescence measurements reflect that the energy state filling, thermal activation, quenching, and lifetime of the carriers in InAs/GaAs0.89Sb0.11 QDs are different from those in the InAs/GaAs0.85Sb0.15 QDs. These differences are attributed to the band alignment transition from type-I to type-II resulting from the Sb-composition change from x = 0.11 to x = 0.15 in the GaAs1-xSbx capping layer. Therefore, the emission and quenching involve excited states for type-I InAs/GaAs0.85Sb0.15 QDs, but involve InAs QDs as well as the GaAs0.85Sb0.15 QW recombination for type-II InAs/GaAs0.85Sb0.15 QDs. So the luminescence reveals complex and distinct physics mechanisms for these two samples.

Strain relaxation in InAs quantum dots through capping layer variation and its impact on the ultrafast carrier dynamics

Ultrafast carrier dynamics is found to be crucial for influencing the efficiency of quantum dot (QD)-based optoelectronic devices. Here, we have studied picosecond resolved dynamics in InAs semiconductor quantum dots forming various heterostructure geometries with their different capping layers. The carriers (electron-hole pairs) are optically injected into three dimensional heterostructure barriers after which, we monitor the carrier relaxation into the zero-dimensional InAs dots by using picosecond resolved time correlated single photon counting technique. We have explicitly investigated and analyzed the effect of three different capping layers, GaAs (binary), In0.15Ga0.85As/GaAs (ternary) and In0.21Al0.21Ga0.58As/GaAs (quaternary) offering various optical properties of InAs quantum dots. It has been observed that quaternary strain reducing layer effectively suppresses Indium migration from the QDs and enhances the confinement of carriers inside the QD heterostructures. In this study, we also find that thermal stability of the carriers is improved in the quaternary capped QDs more effectively compared to the conventional binary and ternary capped one. In brief, our experiments provide essential insight into carrier relaxation in the InAs QDs across various capping layers.

Tuning the optical properties of InAs QDs by means of digitally-alloyed GaAsSb strain reducing layers

In this work, we demonstrate the use of a digitally alloyed GaAsSb as a strain reducing layer (SRL) to tune the optical properties of InAs quantum dots grown on GaAs substrates. The GaAsSb digital alloy was made using a short period GaAs/GaSb superlattice. Increasing the Sb-shutter duty cycle (Sb-SDC) from 0 to 0.35 redshifts the emission wavelength from 1220 nm to 1492 nm at 300 K. The wavelength red shift is attributed mainly to the increased Sb content in the GaAsSb SRL as confirmed by high resolution X-ray diffraction. Power dependent photoluminescence showed a type II band alignment for the samples grown with a Sb-SDC of 0.25 and 0.35. Reversing the growth order of GaAs and GaSb layers and maintaining the same Sb-SDC (0.25) drastically alters the optical properties of the QDs. A large wavelength blue shift of 143 nm and a transformation from a type II to type I emission were observed as a result of GaSb intermixing with InAs QDs.

Fine structure of excitons in InAs quantum dots on GaAs(110) planar layers and nanowire facets

We investigate the optical properties of InAs quantum dots grown by molecular beam epitaxy on GaAs(110) using Bi as a surfactant. The quantum dots are synthesized on planar GaAs(110) substrates as well as on the {110} sidewall facets of GaAs nanowires. At 10 K, neutral excitons confined in these quantum dots give rise to photoluminescence lines between 1.1 and 1.4 eV. Magneto-photoluminescence spectroscopy reveals that for small quantum dots emitting between 1.3 and 1.4 eV, the electron-hole coherence length in and perpendicular to the (110) plane is on the order of 5 and 2 nm, respectively. The quantum dot photoluminescence is linearly polarized, and both binding and antibinding biexcitons are observed, two findings that we associate with the strain in the (110) plane This strain leads to piezoelectric fields and to a strong mixing between heavy and light hole states, and offers the possibility to tune the degree of linear polarization of the exciton photoluminescence as well as the sign of the binding energy of biexcitons.

Influence of GaAsSb structural properties on the optical properties of InAs/GaAsSb quantum dots

The optical properties of InAs quantum dots with GaAsSb buffer, capping and cladding layers of different alloy compositions are studied by photoluminescence techniques. Fully strained GaAsSb layers show that the inclusion of a buffer layer gives a blue-shift to quantum dot emission, while for quantum dots capped with GaAsSb a clear red-shift is seen. Power-dependent photoluminescence suggests a transition from type-I to type-II can be achieved by GaAsSb at Sb composition between 11–13%, while the transition for the GaAsSb cladding layer occurs at around 11%. At low Sb composition, good crystal quality and energy barrier are detected by temperature-dependent photoluminescence, while high-level dislocation and defects exist under high antimony content, as evidenced by X-Ray Diffraction and Transmission Electron Microscopy.

Effects of Sb incorporation in GaAsSb-capping layer on the optical properties of InAs/GaAs QDs grown by Molecular Beam Epitaxy

We have investigated the effect of antimony incorporation in GaAsSb as a capping layer on the optical properties of InAs quantum dots grown by Molecular Beam Epitaxy. Atomic Force Microscopy (AFM), High Resolution X-Ray Diffraction (HRXRD), photoluminescence (PL) and power dependent PL at 77 K and 300 K have been used for the characterization of the grown samples. Our analysis showed that the emission wavelength increases with Sb content and reaches ∼1.5 μm for Sb concentration of 22%. To achieve this wavelength, a reduction of the growth temperature of the GaAsSb layer from 500 °C to 440 °C was necessary. The wavelength increase is accompanied by a transition from a type I to type II band alignment and a broadening of the PL spectrum to a value of ∼237 nm for an excitation power of 100 mW. This broadening is attributed to the QD size inhomogeneity increase and Sb atoms redistribution during the in-situ annealing during the growth of the barriers at elevated temperature. Our results show the potential of the InAs/GaAsSb system in the development of broadband light sources and super-luminescent light emitting diodes in 1.2–1.5 μm wavelength range.

Investigation of carrier dynamics in InAs/GaAsSb quantum dots with different silicon delta-doping levels

The optical properties of InAs quantum dots (QDs) embedded in a GaAsSb matrix with different delta (δ)-doping levels of 0, 2, 4, and 6 electrons per dot (e−/dot), incorporated to control the occupation of QD electronic states, are studied by photoluminescence (PL) spectroscopy. The time-resolved PL data taken at 10 K reveal that the increase of δ-doping density from 2 to 6 e−/dot decreases the recombination lifetime of carriers at ground states of the QDs from 996 ± 36 to 792 ± 19 ps, respectively. Furthermore, the carrier lifetime of the sample with 4 e−/dot is found to increase at a slower rate than that of the undoped sample as temperature increases above 70 K. An Arrhenius plot of the temperature dependent PL intensity indicates that the thermal activation energy of electrons in the QDs, required for carrier escape from the dot ground state to continuum state, is increased when the δ-doping density is high enough (>4 e−/dot). These results are attributed to the enhanced Coulomb interaction of electrons provided by the δ-doping, leading to reduced thermal quenching of the PL.

Improved optical properties of InAs quantum dots for intermediate band solar cells by suppression of misfit strain relaxation

The properties of InAs quantum dots (QDs) have been studied for application in intermediate band solar cells. It is found that suppression of plastic relaxation in the QDs has a significant effect on the optoelectronic properties. Partial capping plus annealing is shown to be effective in controlling the height of the QDs and in suppressing plastic relaxation. A force balancing model is used to explain the relationship between plastic relaxation and QD height. A strong luminescence has been observed from strained QDs, indicating the presence of localized states in the desired energy range. No luminescence has been observed from plastically relaxed QDs.

Growth of highly dense InAs quantum dots with improved crystal quality embedded in an InGaAsSb quantum well

We investigate the structural and optical properties of InAs quantum dots (QDs) embedded in InxGa1−xAs0.96Sb0.04 layers with different In content. Indium incorporation from 0 to 9% increases QD areal density up to 9.3 × 1010 cm−2 and decreases QD diameter and height by the reduction of the island–island interaction. The elastic strain of the InGaAsSb layers, surrounded by a GaAs matrix, increases with higher In content. Further, the increase of In content from 5 to 9% reduces the density of dislocation loops in the InGaAsSb and GaAs layers almost by half due to improvement of the InAs/InGaAsSb interface quality. The photoluminescence peak from the QDs is redshifted with increasing In content as a result of reduced strain inside the QDs.

Regularities of ion-beam-induced crystallization and properties of InAs-QD/GaAs(001) semiconductor nanoheterostructures

A novel method of the ion-beam-induced crystallization of quantum-size semiconductor eterostructures has been proposed. Using atomic force (AFM) and transmission electron microscopy (TEM), the capacitance–voltage (C–V) method, and photoluminescence (PL) measurements, we have studied the main regularities of ion-beam-induced crystallization and the properties of InAs quantum dots (QDs) on GaAs single crystal substrates with (001) crystallographic orientation as functions of temperature, ion current, and ion energies. It is shown that, in order to grow InAs hut structures, the optimal temperature range is from 500 to 550°C. An intense development of dome clusters is observed at higher temperatures. It is found that an increase in the ion current in an interval from 60 to 120 μA at a temperature of 500°C and an ion energy of 150 eV inconsiderably affects the average sizes of nanoislands. It is shown that, in an ion energy range from 150 to 200 eV and at a constant temperature of the process of 500°C and bam current of 120 μA, bands of stability of medium sizes (∼15 nm) and surface density (∼1011 cm–2) are observed.

Effects of thickness and V/III ratio of low temperature capping layer growth to the optical properties of InAs quantum dots

To achieve increased device performance, the authors systematically explored the dependence of the optical characteristics of InAs quantum dot (QD) ensembles grown via molecular beam epitaxy with different V/III ratios and thicknesses of the low temperature GaAs capping layers. In addition, the paper discusses the mechanism behind the dependence. Experiments showed the QD optical properties were significantly dependent on the GaAs capping layer V/III ratio and the initial GaAs capping layer thickness. An optimized V/III ratio and GaAs capping thickness is reported.