Low-density InAs Quantum Dots Research Articles

Origin of spectral brightness variations in InAs/InP quantum dot telecom single photon emitters

Long-distance quantum communication relies on the ability to efficiently generate and prepare single photons at telecom wavelengths. Low-density InAs quantum dots on InP surfaces are grown in a molecular beam epitaxy system using a modified Stranski–Krastanov growth paradigm. This material is a source of bright and indistinguishable single photons in the 1.3 μm telecom band. Here, the exploration of the growth parameters is presented as a phase diagram, while low-temperature photoluminescence and atomic resolution images are presented to correlate structure and spectral performance. This work identifies specific stacking faults and V-shaped defects that are likely causes of the observed low brightness emission at 1.55 μm telecom wavelengths. The different locations of the imaged defects suggest possible guidance for future development of InAs/InP single photon sources for c-band, 1.55 μm wavelength telecommunication systems.

Early nucleation stages of low density InAs quantum dots nucleation on GaAs by MOVPE

An investigation of ultra-thin InAs layers deposited on GaAs is carried out combining theoretical calculations with results of high-resolution transmission electron microscopy, atomic force microscopy and photoluminescence. Five period InAs/GaAs epilayers were grown by metalorganic vapor phase epitaxy at a very low growth rate, with different InAs deposition times, in order to investigate the morphological and optical evolution from extended 2D InAs flat areas of various thicknesses, starting at 1 monolayer, to the nucleation of 3D InAs islands. The coexistence of extended monolayer-flat 2D terraces of different thicknesses and 3D islands is demonstrated. Optically active InAs 2D terraces with a thickness beyond the critical value are detected. For longer deposition times, quantum dots are nucleated and their size increases at the expense of the 3 monolayer thick 2D layers.

Fabrication of GaAs/AlAs micro-pillar cavities including low-density InAs quantum dots and their photoluminescence properties

Low-density InAs quantum dots (QDs) were grown by intermittent supply method in molecular beam epitaxy. QD density was controlled in a wide range of 106 to 109 cm−2 by in-situ monitoring of RHEED specular-beam intensity. Low-density InAs QDs were embedded into GaAs/AlAs micro-pillar cavity structure, which was fabricated by anisotropic wet-etching through a conventional photoresist mask. Photoluminescence (PL) spectra of single InAs QD in the micro-cavity were analyzed, and its PL intensity was three times higher than that without the cavity.

Low-density InP-based quantum dots emitting around the 1.5 μm telecom wavelength range

The authors report on low-density InAs quantum dots (QDs) grown on AlGaInAs surfaces lattice matched to InP using post-growth annealing by solid-source molecular beam epitaxy. Clearly spatially separated QDs with a dot density of about 5 × 108 cm−2 are obtained by using a special capping technique after the dot formation process. High-resolution micro-photoluminescence performed on optimized QD structures grown on distributed Bragg reflector exhibits single QD emissions around 1.5 μm with narrow excitonic linewidth below 50 μeV, which can be used as single photon source in the telecom wavelength range.

In situ accurate control of 2D-3D transition parameters for growth of low-density InAs/GaAs self-assembled quantum dots

A method to improve the growth repeatability of low-density InAs/GaAs self-assembled quantum dots by molecular beam epitaxy is reported. A sacrificed InAs layer was deposited firstly to determine in situ the accurate parameters of two- to three-dimensional transitions by observation of reflection high-energy electron diffraction patterns, and then the InAs layer annealed immediately before the growth of the low-density InAs quantum dots (QDs). It is confirmed by micro-photoluminescence that control repeatability of low-density QD growth is improved averagely to about 80% which is much higher than that of the QD samples without using a sacrificed InAs layer.

Shape evolution of low density InAs quantum dots in the partial capping process by using As2 source

Shape changes in the capping process of low density InAs quantum dots (QDs) with a thin GaAs layer under As4 and As2 conditions were investigated by atomic force microscopy. The shapes of the capped QDs differ considerably depending on the used arsenic source, As4 or As2. In the case of the As4 source, the QD shape elongated along the [1¯10] direction with the increase in the capping temperature, whereas the elongation along the [1¯10] direction is small compared to that along the [1¯10] direction. On the other hand, in the case of As2, the elongation along the [1¯10] direction is lesser than that in the As4 case. In addition, the elongation along the [110] direction is promoted even at a low capping temperature. In the case of As2, isotropic capping of the QDs can be achieved at a higher capping temperature compared to the case using As4.

Low-Density InAs Quantum Dots Growth by Molecular Beam Epitaxy

We investigate the growth of low-density(~4×108cm-2) InAs quantum dots (QDs) on GaAs by molecular beam epitaxy,with emission wavelength up to 1.3 µm at room temperature were achieved. The QDs density are sensitive to growth temperature,growth rate.The optical properties of the QDs annealing temperature used after spacer layer growth that is attributed to the suppressed In segregation from the QDs into the cap layer, reduced the strain in the QDs,significant decrease of integrated PL intensity was observed as the annealing temperature increases.

Low-density InAs QDs with subcritical coverage obtained by conversion of In nanocrystals

We report growth of InAs/GaAs quantum dots (QDs) by molecular beam epitaxy with low density of 2μm−2 by conversion of In nanocrystals deposited at low temperatures. The total amount of InAs used is about one monolayer, which is less than the critical thickness for conventional Stranski–Krastanov QDs. We also demonstrate the importance of the starting surface reconstruction for obtaining uniform QDs. The QD emission wavelength is easily tunable upon post-growth annealing with no wetting layer signal visible for short anneals. Microphotoluminescence measurements reveal well separated and sharp emission lines of individual QDs.

Design and realization of low density InAs quantum dots on AlGaInAs lattice matched to InP(0 0 1)

We present detailed growth studies of InAs nanostructures grown on Al x Ga y In (1− x− y) As lattice matched to an InP(0 0 1) substrate using molecular beam epitaxy. Highly elongated quantum dash like structures are typically favoured in this material system, due to very anisotropic migration lengths along the [1 −1 0] and [1 1 0] directions. In order to increase the short migration length along the [1 1 0]-direction we used ultra low growth rates down to 3×10 −3 monolayers per second. We show that this offers the possibility to form InAs quantum dots with a low surface density, in contrast to the most commonly formed quantum dash structures. To tailor the emission wavelength of the quantum dots, three methods were studied: (i) the variation of the bandgap of the surrounding material by adjusting the aluminium to gallium ratio, (ii) the variation of the bandgap of the quantum dot material by incorporating antimony and (iii) the variation of the height of the quantum dots by closely stacking two layers of quantum dots upon each other.

Low-Density InAs Quantum Dots Grown on InP(001) Using Solid-Source Molecular Beam Epitaxy with a Post-Growth Annealing Process

Low-density InAs quantum dots (QDs) with a large lateral size were grown on InP(001) by solid-source molecular beam epitaxy with a post-growth annealing process. A decrease in QD density with the amount of InAs deposited was shown by atomic force microscopy, and a density of 5×108 QDs/cm2 was obtained for 0.8 monolayer InAs deposition. Moreover, we found that the growth mechanism of QDs changed significantly depending on the amount of InAs deposited in the vicinity of critical thickness, even if the same annealing condition was applied. Near-field photoluminescence spectroscopy of single QDs demonstrated the high optical qualities of low-density QDs.

Site-controlled InAs quantum dots grown on a 55 nm thick GaAs buffer layer

We present site-controlled low density InAs quantum dots grown by molecular beam epitaxy with a template based overgrowth technique allowing enlarged buffer layers upto 55 nm. Growing a seeding layer of InAs quantum dots in etched holes reduces closing of the holes, so that a second layer of InAs quantum dots can be aligned to the holes after a buffer layer overgrowth. Confocal microphotoluminescence measurements show a significant decrease of the low temperature photoluminescence linewidth of the quantum dots to an average value of ∼500 μeV and a minimum width of 460 μeV. This is to be compared to 2 to 4 meV of quantum dots grown on thin buffer layers. This improvement is due to the enlarged distance to residual defects at the overgrown surface.

Desorption and Ripening of Low Density InAs Quantum Dots

In this paper, combining low deposition rate with proper growth temperature, we have developed a way to prepare very low-density quantum dots (QDs) suited for the study of single QD properties without resorting to submicron lithography. Experiment results demonstrate that InAs desorption is significant during growing the low density QDs. Ripening of InAs QDs is clearly observed during the post-growth annealing. Photoluminescence spectroscopy reveals that the emission wavelength of low density InAs QDs arrives at 1332.4 nm with a GaAs capping layer.

Low density InAs quantum dots with control in energy emission and top surface location

In this work we extend the droplet epitaxy growth technique to the fabrication of low density InAs quantum dots (QDs) on GaAs (001) substrates with control in size, energy emission, and top surface location. In particular, depending on the amount of InAs material deposited, it has been possible to tune the QD energy emission over a range of 1.12–1.40 eV while keeping constant the nanostructures density at 2×108 cm−2. Moreover, the capping growth process of these QD shows mounding features that permit their spatial identification once embedded by a GaAs capping layer.

Growth-interruption-induced low-density InAs quantum dots on GaAs

We investigate the use of growth interruption to obtain low-density InAs quantum dots (QDs) on GaAs. The process was realized by Ostwald-type ripening of a thin InAs layer. It was found that the optical properties of the QDs as a function of growth interruption strongly depend on InAs growth rate. By using this approach, a low density of QDs (4 dots/μm2) with uniform size distribution was achieved. As compared to QDs grown without growth interruption, a larger energy separation between the QD confined levels was observed, suggesting a situation closer to the ideal zero-dimensional system. Combining with an InGaAs capping layer such as In-rich QDs enable 1.3 μm emission at 4 K.

低密度长波长InAs量子点的生长与特性

The growth parameters affecting the deposition of self-assembled InAs quantum dots (QDs) on GaAs substrate by low-pressure metal-organic chemical vapor deposition (MOCVD) are reported. The low-density InAs QDs (~5×10^8 cm^(-2) are achieved using high growth temperature and low InAs coverage. Photoluminescence (PL) measurements show the good optical quality of low-density QDs. At room temperature, the ground state peak wavelength of PL spectrum and full-width at half-maximum (FWHM) are 1361 nm and 23 meV (35 nm), respectively, which are obtained as the GaAs capping layer grown using triethylgallium (TEG) and tertiallybutylarsine (TBA). The PL spectra exhibit three emission peaks at 1361, 1280, and 1204 nm, which correspond to the ground state, the first excited state, and the second excited state of the QDs, respectively.

Extremely Low Density InAs Quantum Dots with No Wetting Layer

Extremely low density InAs quantum dots (QDs) are grown by molecularbeam droplet epitaxy. The gallium deposition amount is optimized tosaturate exactly the excess arsenic atoms present on the GaAs substratesurface during growth, and low density InAs/GaAs QDs(4×106 cm−2) are formed by depositing 0.65 monolayers(MLs) of indium. This is much less than the critical depositionthickness (1.7 ML), which is necessary to form InAs/GaAs QDs with theconventional Stranski–Krastanov growth mode. The narrowphotoluminescence linewidth of about 24 meV is insensitive to cryostattemperatures from 10 K to 250 K. All measurements indicate that there isno wetting layer connecting the QDs.

Low density InAs quantum dots grown on GaAs nanoholes

A growth technique combining droplet epitaxy and molecular beam epitaxy (MBE) is developed to obtain a low density of InAs quantum dots (QDs) on GaAs nanoholes. This growth technique is simple, flexible, and does not require additional substrate processing. It makes possible separate control of the QD density via droplet epitaxy and the QD quality via MBE growth. In this letter the authors report the use of this technique to produce InAs QDs with a low density of 2.7×108cm−2 as well as good photoluminescence properties. The resulting samples are suitable for single QD device fabrication and applications.

Extremely low density InAs quantum dots realized in situ on (100) GaAs

Extremely low density self-assembled InAs quantum dots are grown by acombination technique of in situ annealing for 2 min and pause of substraterotation during molecular beam epitaxy. The surface morphology and structuralcharacteristics of the quantum dots are scrutinized by atomic force microscopy andphotoluminescence spectra. It is found that the quantum dot size and densityincrease as the InAs deposition amount rises. Quantum dots with a density between2.5 × 107 cm−2 and 2.2 × 108 cm−2 are 2–5 nm in height and 18–39 nm in diameter. It is believed that as-grown InAs nanodotsmay be of important value for future single quantum dot research.