InAs Quantum Dots Research Articles

Quantum Dot Photoluminescence Enhancement in GaAs Nanopillar Oligomers Driven by Collective Magnetic Modes.

Single photon sources based on semiconductor quantum dots are one of the most prospective elements for optical quantum computing and cryptography. Such systems are often based on Bragg resonators, which provide several ways to control the emission of quantum dots. However, the fabrication of periodic structures with many thin layers is difficult. On the other hand, the coupling of single-photon sources with resonant nanoclusters made of high-index dielectric materials is known as a promising way for emission control. Our experiments and calculations show that the excitation of magnetic Mie-type resonance by linearly polarized light in a GaAs nanopillar oligomer with embedded InAs quantum dots leads to quantum emitters absorption efficiency enhancement. Moreover, the nanoresonator at the wavelength of magnetic dipole resonance also acts as a nanoantenna for a generated signal, allowing control over its radiation spatial profile. We experimentally demonstrated an order of magnitude emission enhancement and numerically reached forty times gain in comparison with unstructured film. These findings highlight the potential of quantum dots coupling with Mie-resonant oligomers collective modes for nanoscale single-photon sources development.

High-temperature continuous-wave operation of 1310 nm InAs/GaAs quantum dot lasers

Here we report 1.3 μm electrical injection lasers based on InAs/GaAs quantum dots (QDs) grown on a GaAs substrate, which can steadily work at 110 °C without visible degradation. The QD structure is designed by applying the Stranski–Krastanow growth mode in solid source molecular beam epitaxy. The density of InAs QDs in the active region is increased from 3.8 × 1010 cm−2 to 5.9 × 1010 cm−2. As regards laser performance, the maximum output power of devices with low-density QDs as the active region is 65 mW at room temperature, and that of devices with the high-density QDs is 103 mW. Meanwhile the output power of high-density devices is 131 mW under an injection current of 4 A at 110 °C.

Optimization of heterogeneously integrated InP-Si on-chip photonic components.

We demonstrate comprehensive numerical studies on a hybrid III-V/Si-based waveguide system, serving as a platform for efficient light coupling between an integrated III-V quantum dot emitter to an on-chip quantum photonic integrated circuit defined on a silicon substrate. We propose a platform consisting of a hybrid InP/Si waveguide and an InP-embedded InAs quantum dot, emitting at the telecom C-band near 1550 nm. The platform can be fabricated using existing semiconductor processing technologies. Our numerical studies reveal nearly 87% of the optical field transfer efficiency between geometrically-optimized InP/Si and Si waveguides, considering propagating field along a tapered geometry. The coupling efficiency of a directional dipole emission to the hybrid InP/Si waveguide is evaluated to ∼38%, which results in more than 33% of the total on-chip optical field transfer efficiency from the dipole to the Si waveguide. We also consider the off-chip outcoupling efficiency of the propagating photon field along the Si waveguide by examining the normal to the chip plane and in-plane outcoupling configurations. In the former case, the outcoupling amounts to ∼26% when using the circular Bragg grating outcoupler design. In the latter case, the efficiency reaches up to 8%. Finally, we conclude that the conceptual device's performance is weakly susceptible to the transferred photon wavelength, offering a broadband operation within the 1.5-1.6 µm spectral range.

Multi-zone resonance spectrometry of inelastic electron scattering of light and the manifestation of strong spin-orbit interaction in nanostructures with quantum dots

Highly sensitive methods of inelastic light scattering spectrometry have been developed to detect individual photons in the visible and near-infrared spectral ranges (0.4-1.35) μm. Precision optical measurements of vibrational and electronic states of nanostructures with quantum objects are performed, using the example of quantum-dimensional nanoheterostructures (311)In si-GaAs/InAs with InAs quantum dots. A distinctive attractive feature of such structures with a degenerate valence band of symmetry 8 is the presence of a strong spin-orbit interaction. In this case, the intrinsic moment of the holes can effectively interact with the electric field of the incident light wave. It was found that such interaction causes intense luminescence and inelastic scattering of the light wave in the IR region of the 0.9-1.35 μm spectrum. Effective generation of nonequilibrium electron-hole (e-h) plasma with concentrations n=p=1.0·1017 cm-3 and T_e=T_h=25 K,was revealed under resonant excitation conditions, while the lattice temperature T_L=5.1 K. New mechanisms have been discovered for the formation of an abnormally intense integration spectrum of multiplex inelastic light scattering of a rather complex shape formed by various separable resonant contributions of the processes of quasi-elastic scattering by charge carriers, light scattering by acoustic plasmons of electron-hole plasma, as well as inelastic intra- and inter-band light scattering by heavy holes. It has been established that the anomalous intensity gain of such multi-zone selective resonant light scattering is more than 105 times higher than the intensity of Thomson light scattering on individual charge carriers. There is agreement between the estimated calculated and experimental spectra, and for the most part for the difficult-to-interpret significant width of the observed light scattering line. It is shown that new mechanisms of various contributions to the formation of scattered photon radiation are important diagnostic elements that are clearly manifested in the spectra of the resulting enhanced inelastic light scattering. Keywords: nanostructures, quantum objects, resonant scattering of light by charge carriers, exchange interaction, plasma diagnostics.

Синтез методом молекулярно-пучковой эпитаксии и свойства InAs-квантовых точек в теле AlGaAs нитевидных нанокристаллов

We present the results of experimental studies on the synthesis by molecular-beam epitaxy of AlGaAs nanowires with InAs quantum dots. The morphological, structural, and optical properties of the grown nanostructures have been studied. It is important to note that the emission from quantum dots is observed in the wavelength range from 750 to 970 nm. Assumptions about the nature of short-wavelength emission from quantum dots are formulated. In particular, one of the reasons may be a significant desorption of indium atoms and the presence of gallium atoms in catalyst drops during the growth at a substrate temperature of 510◦C. The proposed technology opens up new possibilities for integration direct-gap III−V materials with a silicon platform for various applications in photonics and quantum communications.

Особенности структуры поверхности и поверхностного электронного транспорта в коррелированном топологическом изоляторе SmB-=SUP=-VI-=/SUP=-

We present the results of experimental studies on the synthesis by molecular-beam epitaxy of AlGaAs nanowires with InAs quantum dots. The morphological, structural, and optical properties of the grown nanostructures have been studied. It is important to note that the emission from quantum dots is observed in the wavelength range from 750 to 970 nm. Assumptions about the nature of short-wavelength emission from quantum dots are formulated. In particular, one of the reasons may be a significant desorption of indium atoms and the presence of gallium atoms in catalyst drops during the growth at a substrate temperature of 510◦C. The proposed technology opens up new possibilities for integration direct-gap III−V materials with a silicon platform for various applications in photonics and quantum communications.

Investigation of size and barrier dependent efficiency in InAs quantum dot solar cells

Semiconductor Quantum Dots have unique properties, such as the quantum size effect that provide the breakthrough in optoelectronic devices. The small effective mass of electron and hole open-up an avenue of wide bandgap tunability in InAs Quantum Dots (QDs), making them an attractive material for solar cell application. Therein, 4x4 Luttinger Kohn Hamiltonian method is used to calculate the absorption co-efficient of epitaxially grown InAs QDs. Further, we studied the size-dependent absorption co-efficient and the barrier material model of InAs QDs capping with InP and GaAs. Our theoretical simulation predicts the efficiency of InAs/GaAs and InAs/InP system in the intrinsic layer of p-i-n structure solar cells.

Improving structure design of active region of InAs quantum dots by using InAs/GaAs digital alloy superlattice

A 1.3-μm InAs quantum dot laser has been successfully fabricated on a GaAs(100) substrate by molecular beam epitaxy (MBE) technique through using InAs/GaAs digital alloy superlattices instead of the conventional InGaAs layer. The samples grown by conventional growth method and the digital alloy superlattice growth method are characterized by atomic force microscope (AFM) and photoluminescence (PL) spectroscopy. It is found that 8-period sample possesses a low quantum dot density and poor luminescence performance. With the increase of the number of growth periods, the quantum dot density of the sample increases and the luminous performance improves. This indicates that the quality of the grown sample improves with the increase of InAs/GaAs period of the InGaAs layer. When the total InAs/GaAs period is 32, the quantum dot density of the sample is high and the luminescence performance is good. After the experimental measurement, the sample DAL-0 fabricated by conventional growth method and the sample DAL-32 (32-periods InAs/GaAs digital alloy superlattices) are utilized to fabricate quantum dot laser by standard process. The performances of two types of quantum dot lasers obtained with different growth methods are characterized. It is found that the InAs quantum dot lasers fabricated by the sample grown by digital alloy superlattice method have good performances. Under continuous wave operation mode, the threshold current is 24 mA corresponding to a threshold current density of 75 A/cm<sup>2</sup>. The highest operation-temperature reaches 120 ℃. In addition, InAs quantum dot laser using digital alloy superlattice has good temperature stability. Its characteristic temperature is 55.4 K. Compared with the traditional laser, the InAs quantum dot laser grown by InAs/GaAs digital alloy superlattice has good performance in terms of threshold current density, output power and temperature stability, which indicates that high-quality laser can be obtained by this growth method. Using the InAs/GaAs digital alloy superlattice growth method, the InGaAs composition can be changed without changing the temperature of the source oven. Thus InAs quantum dot lasers with different luminescence wavelengths can be obtained through this growth method. The InAs/GaAs digital alloy superlattice structure can be used to realize different averaging of In content in the growth structure. The method provides a new idea for designing and growing the active region of quantum dot laser.

Physical probing of quantum energy levels in a single indium arsenide (InAs) quantum dot.

Indium arsenide (InAs) quantum dots (QDs) grown by molecular beam epitaxy (EBM) on gallium arsenide (GaAs) substrates have exhibited quantized charge-trapping characteristics. An electric charge can be injected in a single QD by a gold-coated AFM nano-probe placed directly on it using a conductive-mode atomic force microscope (C-AFM). The results revealed separate current-voltage (I-V) curves during consecutive measurements, where the turn-on voltages measured at the subsequent voltage sweeps are incrementally lower than that at the initial sweep. We demonstrate that the charge state of the QD can change over a long enough time by measuring the I-V data on the same QD at different time intervals. Discrete energy states (here, five states) have been observed due to the quantized charge leakage from the QD into the surrounding materials. These quantum states with five energy levels have been verified using quantum theory analysis of the quantum-well with the help of a numerical simulation model, which depends on the QD dimensions. The size of the quantum-well in the model is in good agreement with the actual QD size, whose lateral dimension is confirmed using a scanning electron microscope. At the same time, the height is estimated from the atomic force microscope topography.

Theoretical Study on Vertically Coupled Stranski-Krastanov (SK) on Sub Monolayer (SML) InAs Quantum Dot Heterostructures Employing Ternary and Quaternary Barrier Materials

This work presents the impact of barrier spacer on the structural and optical properties of strain-coupled Stranski-Krastanov (SK) on Sub Monolayer (SML) quantum dot (QD) heterostructures. Various ternary and quaternary materials have been employed as the barrier layer of SK-SML QD heterostructures. In the coupled SK-SML QDs, the residual strain propagates from the SML seed layer towards the top SK dots, introducing defects and dislocations. After employing the ternary (GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) and quaternary (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.21</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-.0.21-x</sub> As and In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.18</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.82</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-y</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> ) materials, the residual strain reduces, reducing the defects which thereby helps in increasing the crystalline quality of the heterostructure. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Nextnano</i> software has been used to compute the structures' strain, energy band profile, probability density functions, and emission wavelength. Two strain components, viz. hydrostatic as well as biaxial strain, have been computed and compared for all the heterostructures to understand the distribution of the strain profile. The emission wavelength is red-shifted for the SK-SML QD heterostructures with ternary and quaternary materials as a barrier layer as compared to that of the GaAs barrier. Moreover, type-I and II energy band profiles are observed for Sb-based barrier material, appropriate for various optoelectronic applications. This is a comparative study of SK-SML QDs with various barrier materials helps minimize the strain and defects and improve the device performance.

Формирование наноостровков InAs на поверхности кремния и гетероструктур на их основе

Experimental results of studying the InAs islands formation of silicon surface by molecular beam epitaxy are presented. It has been found that, InAs islands with both bimodal and uniform size distributions can be formed depending on the Si surface relief and the presence of nanopits. The possibility of fabricating heterostructures with InAs quantum dots demonstrating photoluminescence in the region of 1.65 μm, was showed.

Влияние давления мышьяка при заращивании квантовых точек InAs тонким низкотемпературным слоем GaAs на их оптические свойства

This paper presents the results of the experimental studies of InAs quantum dot overgrowth by a low-temperature GaAs layer at different arsenic vapor pressures. It is revealed that a threefold decrease in the arsenic pressure at a fixed deposition rate of the capping layer leads to a change in the shape of the photoluminescence spectrum of quantum dots with one maximum at the level of 1.19 eV to the shape of the spectrum with two low-energy contributions at the levels of 1.08 and 1.15 eV. Based on the analysis of the power dependences of the photoluminescence spectra, it is found that the low-energy contributions of the photoluminescence of quantum dots overgrown at a low arsenic pressure correspond to the ground-state emission two groups of quantum dots with different average sizes formed during mass transfer in the “quantum dot – wetting layer – matrix” system.

Room-temperature electric field control of spin filtering efficiency for enhanced modulation of optical spin polarization in a defect-functional 0D-2D hybrid nanostructure.

In order to accomplish spin-based photoelectric information processing, it is necessary to modulate electron spin polarization in III-V semiconductor quantum dots (QDs) using an electric field. However, there is a principal limitation to the spin polarization degree and its control range, as the electron spin polarization is rapidly lost during injection into the QDs at room temperature (RT). Here, electric field control of optical spin polarization in the range of 15-40% is demonstrated at RT using InAs QDs tunnel-coupled with a defect-functional GaNAs quantum well (QW) spin filter. This compares with an electric field control of 1-4% for InAs QDs tunnel-coupled with an InGaAs QW. Transient polarization in the range of 30-60% is also obtained in the ultrafast time domain of less than 100 ps, the degree of polarization depending on the electric field. The enhanced polarization control is achieved by tuning the amplified spin polarization of electrons tunnel-injected from the GaNAs QW into QDs via the electric-field-dependent spin-filtering efficiency of GaNAs. These findings will provide a new way to extensively modulate the electron spin polarization in opto-semiconductors, by electric-field-induced on/off switching of spin amplification.

A self-assembling method to align metal nanoparticles to quantum dots

Hybrid nanostructures are known to elicit an enhanced optical response due to plasmonic coupling effects. A relevant material system of current interest is InAs-ErAs composite structure where semi-metallic ErAs nanoparticles (NPs) are coupled to InAs quantum dots (QDs). In order to achieve well-defined coupling, a precise alignment must occur between the QD and metal NP. However, the low migration of Er on III-V surfaces (due to strong bond strength) combined with random nucleation of QDs prevents accurate placement. Here we report a novel way to potentially address both these issues, where direct assembly of ErAs metal NPs over InAs QDs is achieved with molecular beam epitaxy (MBE). Using the strain driven nucleation mechanism we show that lightly Er doped InAs QDs can be self-aligned to underlying InAs QDs. Annealing uncapped Er:InAs QDs at high temperature desorbs the In atoms in QD. However, due to much lower volatility and limited solubility, Er atoms condense out and nucleate as ErAs NPs that align with the underlying InAs QDs. This method can potentially position other low-mobility materials (in our case ErAs) amenable to directed assembly processes of a higher mobility component (in this case InAs). To be successful the higher mobility/volatility component must be capable of dissolving the low mobility/volatility component without significantly changing its directed assembly process.

Zn-Doped P-Type InAs Nanocrystal Quantum Dots.

Doped heavy metal-free III-V semiconductor nanocrystal quantum dots (QDs) are of great interest both from the fundamental aspects of doping in highly confined structures, and from the applicative side of utilizing such building blocks in the fabrication of p-n homojunction devices. InAs nanocrystals (NCs), that are of particular relevance for short-wave IR detection and emission applications, manifest heavy n-type character poising a challenge for their transition to p-type behavior. The p-type doping of InAs NCs is presented with Zn - enabling control over the charge carrier type in InAs QDs field effect transistors. The post-synthesis doping reaction mechanism is studied for Zn precursors with varying reactivity. Successful p-type doping is achieved by the more reactive precursor, diethylzinc. Substitutional doping by Zn2+ replacing In3+ is established by X-ray absorption spectroscopy analysis. Furthermore, enhanced near infraredphotoluminescence is observed due to surface passivation by Zn as indicated from elemental mapping utilizing high-resolution electron microscopy corroborated by X-ray photoelectron spectroscopy study. The demonstrated ability to control the carrier type, along with the improved emission characteristics, paves the way towards fabrication of optoelectronic devices active in the short-wave infrared region utilizing heavy-metal free nanocrystal building blocks.

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.

The Effects of Temperature and Electric Field on the Electronic and Optical Properties of an InAs Quantum Dot Placed at the Center of a GaAs Nanowire

The Effects of Temperature and Electric Field on the Electronic and Optical Properties of an InAs Quantum Dot Placed at the Center of a GaAs Nanowire

Atomic-scale characterization of single and double layers of InAs and InAlAs Stranski-Krastanov quantum dots

We report a detailed structural characterization of single and double layers of InAs and InAlAs quantum dots (QDs) and their wetting layers (WLs) by atomic force microscopy (AFM) and cross-sectional scanning tunneling microscopy (X-STM). The X-STM analysis with atomic resolution showed that the InAlAs WL consists of two distinct layers: a bottom part where all the Al atoms of the InAlAs alloy settled, and a top part containing exclusively In and Ga atoms. The QDs formed from the InAlAs layer contains no Al atoms at all and lie on top of the Al-rich WL. In the double layers of QDs, the InAlAs QDs were used as a seed to influence the nucleation of the InAs QDs grown on top. A gradual decrease in the density of the top InAs QDs was observed in the AFM images with increasing thickness of the GaAs spacer. The X-STM images showed that both QDs layers were completely intermixed for a 2-nm-thick spacer, while effective strain-induced stacking of both types of QDs was observed for a GaAs spacer thickness of 4 nm. However, both QD layers were completely decoupled for a GaAs spacer thickness of 8 nm and could thus be treated as individual layers.

Surfactant effect of Bi on InAs quantum dot laser diode

In this study, InAs multiple-stacked quantum dot lasers were investigated in the 1.55 μm band using the Bi surfactant effect. The Bi surfactant effect increased the size of the quantum dot and changed the emission wavelength from 1522 to 1554 nm. Moreover, the surfactant effect enhanced the internal quantum efficiency of the fabricated broad-area laser from 33% to 54%.

An explanation for the non-monotonic temperature dependence of the photoluminescence spectral features of self-organized InAs QDs

Temperature-dependent photoluminescence (PL) measurements under different excitation densities were performed on self-assembled InAs quantum dots (QDs) grown by molecular beam epitaxy. Non-monotonic evolutions in the curves of the PL spectral parameters as a function of the sample temperature were observed in the low-temperature regime. Indeed, the PL peak energy of the QDs shows a sigmoidal variation with increasing temperature. This component is accompanied by an anomalous increase in the integrated intensity over the temperature range of 8–50K. These behaviors have been attributed to the optical emission from deep states that exist in the potential of the dots. A simple rate equation model, which describes the thermally activated emission and trapping of photo-injected carriers, is proposed to illustrate the interpretations made regarding the evolution of the integrated PL intensity with increasing temperature. A good agreement between the model simulation and the PL data was obtained for temperatures ranging from 8 to 300K. It was found that the thermally activated process of the intra-dot redistribution of carriers provides a good description of the anomalous behaviors encountered in the PL investigations depending on the temperature of the QD sample.