Characterization Of InAs Quantum Dots Research Articles

Influence of the Arsenic Pressure during Rapid Overgrowth of InAs/GaAs Quantum Dots on Their Photoluminescence Properties

In this paper, for the first time, we report a strong effect of the arsenic pressure used for the high-rate GaAs capping of self-assembled InAs quantum dots on their optical properties. A 140 nm red shift of the photoluminescence peak position is observed when the overgrowth arsenic pressure increases threefold. We explain this behavior in terms of different intensities of quantum dot decomposition, which occurs during the overgrowth under different conditions. When the arsenic pressure is sufficiently high, a GaAs capping layer is formed by deposited species with a low impact on initial quantum dots. At a low arsenic pressure, arsenic deficiency leads to the intensive intermixing caused both by the enhanced Ga/In atom exchange and by the consumption of arsenic atoms belonging to quantum dots for the GaAs capping layer formation. As a result of the overgrowth, quantum dots are divided into families with a large (high pressure) and a small (low pressure) average size, yielding long-wave (1.23 µm) and short-wave (1.09 µm) photoluminescence peaks, respectively. Thus, a significant influence of the overgrowth arsenic pressure on the characteristics of InAs quantum dots is evidenced in this study.

Особенности роста массивов квантовых точек InAs с низкой поверхностной плотностью методом молекулярно-пучковой эпитаксии

The influence of the substrate temperature and the flux of In adatoms on the structural and optical characteristics of InAs quantum dots with a low surface density is experimentally studied. An increase in the substrate temperature under conditions of a high flux of In adatoms promotes an increase in their surface migration and a certain decrease in the density of the array of quantum dots (down to ~(1-2) 10^10 cm^-2), however, in this case, a significant short-wave shift of the photoluminescence spectrum is observed, despite side points. A decrease in the incident flux of In adatoms at optimum substrate temperatures makes it possible to reduce the dot density more efficiently (down to ~(1-2) 10^9 cm^-2).

Peculiarities of growth of InAs quantum dot arrays with low surface density by molecular beam epitaxy

The influence of the substrate temperature and the flux of In adatoms on the structural and optical characteristics of InAs quantum dots with a low surface density is experimentally studied. An increase in the substrate temperature under conditions of a high flux of In adatoms promotes an increase in their surface migration and a certain decrease in the density of the array of quantum dots (down to ~ (1-2)· 1010 cm-2), however, in this case a significant short-wavelength shift of the photoluminescence spectrum is observed despite an increase in lateral sizes of dots. A decrease in the incident flux of In adatoms at optimal substrate temperatures makes it possible to reduce the dot density more efficiently (down to ~ (1-2)· 109 cm-2). Keywords: molecular-beam epitaxy, quantum dots, surface density.

Photoluminescence (PL) characterization of InAs/GaAs quantum dots (QDs): A theoretical study

It is well known that before using thin films in applications, it is necessary to carry out their characterization because it provides informations on the degree of their quality. In this article, photoluminescence (PL) characterization of InAs Quantum Dots (QDs) embedded in a GaAs matrix is reported. Detailed analysis of PL mechanisms was introduced and illustrated.Analysis of photoluminescence spectra shows that the homogeneity and the density of the Quantum dots (QDs) depend on the temperature. A shift of PL peaks to lower energies with increasing temperature was reported.We have showed that the absorption and emission in QD are governed by the confinement principles.Our simulation model is mainly based on a single QD and temperature dependent photoluminescence (PL). A good agreement with experimental results is obtained.

Structural and Optical Characteristics of InAs QDs Stacked on GaAs Substrate by Molecular Beam Epitaxy

Abstract In recent days, InAs quantum dots (QDs) photo detector is a topic of research because of their potential applications in advanced telecommunication systems and space application. The InAs QDs were grown on semi-insulating GaAs substrates by molecular beam epitaxial (MBE) System. The InAs QDs were stacked nominally with different Spacer Layer (SL) thickness of 5, 10, 15, 25 and 35 nm in order to find the optimized SL thickness. The QDs parameters like height, diameter and dot density were observed by atomic force microscopy (AFM). The QDs were approximately 4-6 nm in height, 15-25 nm in diameter and the areal density was around 3.85 x 1010 cm-2 for 2.4 mono layers (MLs) of single layer QDs grown at 500°C. The photoluminescence (PL) spectra of single layer InAs QDs covered by GaAs layer centered at 1079 nm. For less SL thickness (5, 10 nm) the peak position was red shifted to 1100 nm due to size broadening of QDs. For SL thickness of 35 nm the peak position was around 1084 nm which is almost near to the single layer QDs. The six layers stacked InAs QDs structure was examined by using scanning tunneling microscope (STM) and transmission electron microscope (TEM) to determine the QDs parameters and thickness of the grown layers. The structural and optical characterizations will be discussed in detail.

Effect of Sb and As spray on emission characteristics of InAs quantum dots with AlAs capping layer

We report on the influence of an Sb/As combined spray on the physical and optical characteristics of AlAs-capped InAs/GaAs quantum dots grown by Molecular Beam Epitaxy. Photoluminescence emission from the quantum dots shows a significant peak position shift under different Sb/As spray sequences. A blue-shifted quantum dot emission peak with an initial Sb rest indicates a large-to-small quantum dots transition process, with a bi-modal quantum dot size distribution inferred. High-resolution Transmission Electron Microscopy results reveal a large density of small quantum dots when the Sb spray is treated first. Furthermore, defect passivation in the vicinity of the quantum dots by use of Sb spray was detected.

TEM Characterization of InAs Quantum Dots with GaAsSb Spacer Layers

Journal Article TEM Characterization of InAs Quantum Dots with GaAsSb Spacer Layers Get access A Boley, A Boley Department of Physics, Arizona State University, Tempe, AZ 85287 Search for other works by this author on: Oxford Academic Google Scholar Y Kim, Y Kim School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287 Search for other works by this author on: Oxford Academic Google Scholar K-Y Ban, K-Y Ban School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287 Search for other works by this author on: Oxford Academic Google Scholar C B Honsberg, C B Honsberg School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, AZ 85287 Search for other works by this author on: Oxford Academic Google Scholar D J Smith D J Smith Department of Physics, Arizona State University, Tempe, AZ 85287 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 1656–1657, https://doi.org/10.1017/S1431927616009120 Published: 25 July 2016

Emission-wavelength tuning of InAs quantum dots grown on nitrogen-δ-doped GaAs(001)

We studied the structural and photoluminescence (PL) characteristics of InAs quantum dots (QDs) grown on nitrogen (N) δ-doped GaAs(001). The emission wavelength for low-density N-δ doping exhibited a blueshift with respect to that for undoped GaAs and was redshifted with increasing N-sheet density. This behavior corresponded to the variation in the In composition of the QDs. N-δ doping has two opposite and competing effects on the incorporation of Ga atoms from the underlying layer into the QDs during the QD growth. One is the enhancement of Ga incorporation induced by the lattice strain, which is due to the smaller radius of N atoms. The other is an effect blocking for Ga incorporation, which is due to the large bonding energy of Ga-N or In-N. At a low N-sheet density, the lattice-strain effect was dominant, while the blocking effect became larger with increasing N-sheet density. Therefore, the incorporation of Ga from the underlying layer depended on the N-sheet density. Since the In-Ga intermixing between the QDs and the GaAs cap layer during capping also depended on the size of the as-grown QDs, which was affected by the N-sheet density, the superposition of these three factors determined the composition of the QDs. In addition, the piezoelectric effect, which was induced with increased accumulation of lattice strain and the associated high In composition, also affected the PL properties of the QDs. As a result, tuning of the emission wavelength from 1.12 to 1.26 μm was achieved at room temperature.

Lasing characteristics of InP-based InAs quantum dots depending on InGaAsP waveguide conditions.

We report the influences of a dot-in-a-well structure with a thin GaAs layer and the thickness of a waveguide (WG) on the lasing characteristics of InAs quantum dots (QDs) based on InP. The QD laser diodes (QDLDs) consist of seven-stacked InAs QDs separated by a 10 nm-thick InGaAsP (1.15 μm, 1.15Q-InGaAsP) layer, which is further sandwiched by a 800 nm-thick 1.15Q-lnGaAsP WG (reference QDLD). For comparison, the InAs QDs were inserted into the InGaAsP (1.35 μm, 1.35Q-InGaAsP) quantum well embedded in the 1.15Q-InGaAsP matrix at the active layer. And a 2 monolayer (ML)-thick GaAs layer was additionally introduced right before the QD layer (GDWELL-LDs). Lasing emission from the reference QDLD with only the 1.15Q-InGaAsP structure was not observed at room temperature (RT). However, the lasing emission from the GDWELL-LDs was clearly observed at the wavelength of 1.46 μm at RT under continuous-wave (CW) mode. The threshold current density of the GDWELL-LD with the 800 nm-thick InGaAsP WG was measured to be 830 A/cm2, which was lower than that of the GDWELL-LD with the 200 nm-thick WG (900 A/cm2). Also, the slope efficiency of the GDWELL-LD was significantly improved with increasing thickness of the InGaAsP WG.

Investigation on the lasing characteristics of InAs/InGaAsP quantum dots with additional confinement structures

We report on morphological, optical, and lasing characteristics of InAs quantum dots (QDs) embedded in an In0.69Ga0.31As0.67P0.33 quantum well (having a bandgap energy corresponding to a wavelength of 1.35μm (1.35Q-InGaAsP)), which formed a dot-in-a-well (DWELL) structure. This DWELL was further sandwiched in In0.85Ga0.15As0.32P0.68 layers (1.15μm, 1.15Q-InGaAsP). A 2 monolayer-thick GaAs layer was simultaneously introduced right below the InAs QD layer in the DWELL structure (GDWELL). The emission wavelength of the InAs GDWELL was 1490nm, which was slightly shorter than that of the InAs QDs embedded only in 1.15Q-InGaAsP layers. To evaluate the effects of the GDWELL structure on lasing characteristics, gain-guided broad-area (BA) and index-guided ridge-waveguide (RW) laser diodes (LDs) were fabricated. The BA-LDs with the InAs QDs embedded only in 1.15Q-InGaAsP layers did not show the lasing at room temperature (RT) even in pulsed mode. For the GDWELL structure, however, the lasing emissions from both the BA-LDs and RW-LDs were successfully achieved at RT in continuous-wave mode.

Growth and characterization of InAs quantum dots on InP nanowires with zinc blende structure

InAs quantum dots (QDs) are grown epitaxially on the {112} side facets of InP nanowires (NWs) by metal organic chemical vapor deposition. The QDs typically have a large size and consist of some specific facets. The QDs exhibit mainly zinc blende structure with stacking faults, which is consistent with the adjacent NW. No QDs are observed on the wurtzite (WZ) part of NW, which is attributed to a lower surface energy of WZ facet. The random distribution of the QDs indicates that the In adatoms may mainly come from the vapor rather than the substrate.

Growth and Characterization of InAs Quantum Dots on GaAsSb

The growth details of strained GaAsSb layers on GaAs(001) substrates were studied by reflection high energy electron diffraction (RHEED) beam intensity oscillations as a function of both substrate temperature and Sb/As flux ratio. Both the RHEED intensity and RHEED oscillation cycles are reduced with decreasing substrate temperature and Sb/As flux ratio. InAs QDs with high dot density, small dot size and narrow size distribution have been achieved on strained GaAs / GaAsSb buffer layer. The average lateral size of dots shows a trend toward to smaller size and dots’ density shows a trend toward to higher density as the surface Sb composition increasing. The QDs with higher density and smaller size distributions at high Sb composition, indicates that the Sb plays an important role in the dot formation under this growth condition. The lattice mismatch of InAs layer with the GaAsSb buffer layer is reduced with increasing of Sb composition in the GaAsSb interlayer. This result indicates that the density, size and size distribution of self-assembled quantum dots (QDs) can be controlled through the manipulation of the Sb-mediated strain field in the lattice mismatched system.

Modification in the structural and optical characteristics of InAs quantum dots by manipulating the strain distribution

We report the structural and optical properties of InAs quantum dots (QDs) on GaAs formed by using a modified self-assembled method (MSAM) adopting periodical arsenic interruption. From the atomic force microscopy images, the densities of the InAs QDs and large clusters grown by the conventional self-assembled mode (CSAM) were 7.3 × 1010 /cm2 and 1.9 × 109 /cm2, respectively. However, the density for the MSAM QD sample was significantly increased to 9.5 × 1010 /cm2, and no large clusters were observed at all. Also, the size distribution for the MSAM InAs QDs was improved to 8.9% from that for the CSAM QDs with 13.5%. The improvement in the structural properties of the MSAM InAs QDs can be explained by the modulation in the distribution of the strain field controlled by the growth kinetics of indium migration. Compared to that of the CSAM QDs, the photoluminescence (PL) peak for the MSAM QD sample was red-shifted, and the intensity was enhanced by more than 2.2 times. The PL decay profiles corresponding to the carrier lifetimes of InAs QDs are also discussed in terms of the variations in the structural properties.

Optical investigation of InAs/InP(1 0 0) quantum dots grown by gas source molecular beam epitaxy

We report on the optical characteristics of InAs quantum dots based on the InP(100) substrate grown by gas source molecular beam epitaxy without assisting any other methods. The photoluminescence was carefully investigated by adjusting the thickness of InAs layers and the growth temperature. A wide range of emitting peaks is obtained with the increase in the thickness of InAs layers. In addition, we find that the morphology and shape of quantum dots also greatly depend on InAs layers. The images of atomic force microscopy show that the quantum dots like forming into quantum dashes elongated along the [01−1] direction when the thickness of InAs layers increased. A critical thickness of formation quantum dots or quantum dash is obtained. At the same time, we observe that the growth temperature also has a great impact on the emission wavelength peaks. High qualities of InAs/InP(100) quantum dots providing their emission wavelength in 1.55μm are obtained, and good performances of quantum dots lasers are fabricated.

Directed self-assembly of InAs quantum dots on nano-oxide templates

We describe the growth and characterization of InAs quantum dots on SiO2 patterned GaAs by metal organic chemical vapor deposition. Arrays of quantum dots with densities as high as 1.8×1010 cm−2 fabricated by electron beam lithography are demonstrated. A process consisting of dry and wet etching to minimize etch damage is developed. As the mask diameter increases, the nucleation transitions from single dots to multidot clusters. We achieve more uniform size and shape distributions of dots on patterned regions relative to unpatterned dots as revealed by structural characterization and room temperature photoluminescence emission spectra.

Post-thermal Annealing Effects on Photoluminescence Properties of InAs Quantum Dots on GaNAs Buffer Layer

The thermal annealing characteristics of InAs quantum dots (QDs) on a GaNAs buffer layer grown by the metalorganic chemical vapor deposition were investigated. Although the photoluminescence efficiency was deteriorated by annealing, the improved tolerance in the annealing time and temperature was confirmed in comparison with the GaAs buffer sample. The wavelength blue shift was similar in both buffer layers. The improvements in the PL efficiency were considered to be related to the decreased coalescent QDs upon introducing the dilute-nitrogen into the buffer layer.

Post-thermal Annealing Effects on Photoluminescence Properties of InAs Quantum Dots on GaNAs Buffer Layer

The thermal annealing characteristics of InAs quantum dots (QDs) on a GaNAs buffer layer grown by the metalorganic chemical vapor deposition were investigated. Although the photoluminescence efficiency was deteriorated by annealing, the improved tolerance in the annealing time and temperature was confirmed in comparison with the GaAs buffer sample. The wavelength blue shift was similar in both buffer layers. The improvements in the PL efficiency were considered to be related to the decreased coalescent QDs upon introducing the dilute-nitrogen into the buffer layer.

Effects of a InGaAs Strained Layer on Structures and Photoluminescence Characteristics of InAs Quantum Dots

The influences of a thin InGaAs layer grown on GaAs(100) substrate before deposited InAs self-assembled quantum dots(SAQDs) were experimentally investigated. Scanning electronic microscope (SEM) measurements show that the InGaAs strained layer may release the strain between wetting layer and QDs, and then enlarge size of QDs. When the thickness of InAs layer is small, the QDs are chained. Temperature dependent photoluminescence (TDPL) measurements show that the PL peaks of InAs QDs with In0.1Ga0.9As show much more red shift compared with the QDs directly deposited on GaAs matrix, and PL integral intensity enhances as T rises from 50K to 90K. We attribute this enhancement to the small potential barrier between WL and QDs produced by the InGaAs stained layer.

Memory characteristics of InAs quantum dots embedded in GaAs quantum well

The memory characteristics of InAs based quantum dot (QD) memory devices has been investigated by carrying out capacitance-voltage and current-voltage measurements. The dots which were embedded in the GaAs quantum well were charged by the electrons from the two dimensional electron gas and a clockwise hysteresis loop is observed on cyclically sweeping the gate bias. The number of trapped electrons is found to be two orders of magnitude lesser than the QD density. Interdot Coulombic interactions and phonon assisted electron tunneling was found to significantly affect the charge trapping ability of the QDs.

Photoluminescence Characteristics of InAs Quantum Dots with GaInP Cover Layer Grown by Metalorganic Chemical Vapor Deposition

The photoluminescence (PL) characteristics of InAs quantum dots (QDs) with a GaInP cover layer grown by metalorganic chemical vapor deposition were investigated to clarify the effect of the cover layer. By comparing the PL peak wavelength between the GaInP and GaInAs covered structures, the strain of the cover layer was identified as the main mechanism responsible for the emission wavelength shift of the InAs QDs. The PL emission efficiency and the thermal annealing effect of the GaInP-covered structure were also investigated.