Journal articles: 'GaAs, quantum nanostructures, molecular beam epitaxy, droplet epitaxy'

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Huang, She Song, Zhi Chuan Niu, and Jian Bai Xia. "Self-Assembled GaAs Quantum Rings by MBE Droplet Epitaxy." Solid State Phenomena 121-123 (March 2007): 541–44. http://dx.doi.org/10.4028/www.scientific.net/ssp.121-123.541.

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Fabrication of semiconductor nanostructures such as quantum dots (QDs), quantum rings (QRs) has been considered as the important step for realization of solid state quantum information devices, including QDs single photon emission source, QRs single electron memory unit, etc. To fabricate GaAs quantum rings, we use Molecular Beam Epitaxy (MBE) droplet technique in this report. In this droplet technique, Gallium (Ga) molecular beams are supplied initially without Arsenic (As) ambience, forming droplet-like nano-clusters of Ga atoms on the substrate, then the Arsenic beams are supplied to crystallize the Ga droplets into GaAs crystals. Because the morphologies and dimensions of the GaAs crystal are governed by the interplay between the surface migration of Ga and As adatoms and their crystallization, the shape of the GaAs crystals can be modified into rings, and the size and density can be controlled by varying the growth temperatures and As/Ga flux beam equivalent pressures(BEPs). It has been shown by Atomic force microscope (AFM) measurements that GaAs single rings, concentric double rings and coupled double rings are grown successfully at typical growth temperatures of 200°C to 300°C under As flux (BEP) of about 1.0×10-6 Torr. The diameter of GaAs rings is about 30-50 nm and thickness several nm.

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Thainoi, Supachok, Suwit Kiravittaya, Thanavorn Poempool, Zon, Noppadon Nuntawong, Suwat Sopitpan, Songphol Kanjanachuchai, Somchai Ratanathammaphan, and Somsak Panyakeow. "Molecular beam epitaxy growth of InSb/GaAs quantum nanostructures." Journal of Crystal Growth 477 (November 2017): 30–33. http://dx.doi.org/10.1016/j.jcrysgro.2017.01.011.

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López-López, Máximo, Esteban Cruz-Hernández, Isaac Martínez-Velis, Juan Salvador Rojas-Ramírez, Manolo Ramirez-Lopez, and Álvaro Orlando Pulzara-Mora. "Self Assembly of semiconductor nanostructures." Respuestas 12, no. 2 (May 16, 2016): 47–51. http://dx.doi.org/10.22463/0122820x.570.

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Abstract In this work we present the growth and characterization of GaAs self-assembled quantum wires (SAQWRs), and InAs self-assembled quantum dots (SAQDs) by molecular beam epitaxy on (631)-oriented GaAs substrates. Adatoms on the (631) crystal plane present a strong surface diffusion anisotropy which we use to induce preferential growth along one direction to produce SAQWRs. On the other hand, InAs SAQDs were obtained on GaAs(631) with SAQWRs by the Stransky–Krastanov (S-K) growth method. SAQDs grown directly on (631) substrates presented considerable fluctuations in size. We study the effects of growing a stressor layer before the SAQDs formation to reduce these fluctuations.Keywords : Quantum wires, quantum dots; selfassembly; molecular beam epitaxy.

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Nakai, Takanori, Seiki Iwasaki, and Koichi Yamaguchi. "Control of GaSb/GaAs Quantum Nanostructures by Molecular Beam Epitaxy." Japanese Journal of Applied Physics 43, no. 4B (April 27, 2004): 2122–24. http://dx.doi.org/10.1143/jjap.43.2122.

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Prongjit, P., N. Pankaow, S. Thainoi, S. Panyakeow, and S. Ratanathammaphan. "Formation of GaP nanostructures on GaAs (100) by droplet molecular beam epitaxy." physica status solidi (c) 9, no. 7 (May 21, 2012): 1540–42. http://dx.doi.org/10.1002/pssc.201100798.

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Narabadeesuphakorn, Phisut, Jirayu Supasil, Supachok Thainoi, Aniwat Tandaechanurat, Suwit Kiravittaya, Noppadon Nuntawong, Suwat Sopitopan, Songphol Kanjanachuchai, Somchai Ratanathammaphan, and Somsak Panyakeow. "Growth Control of Twin InSb/GaAs Nano-Stripes by Molecular Beam Epitaxy." MRS Advances 2, no. 51 (2017): 2943–49. http://dx.doi.org/10.1557/adv.2017.510.

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ABSTRACTInSb has been considered as a promising material for spintronic applications owing to its pronounced spin effects as a result of large intrinsic electronic g-factor. In addition, embedding InSb quantum nanostructures in a GaAs matrix could create type-II band alignment, where radiation lifetimes are longer than those of the typical type-I systems. Such characteristics are promising for memory devices and infrared photonic applications. The growth of InSb/GaAs quantum nanostructures by strain driven mechanism using molecular beam epitaxy with low growth temperature, slow growth rate, Sb soaking process prior to In deposition, and small amount of In deposition typically creates a mixture of twin and single nano-stripe structures with truncated pyramid shape. In this work, we further investigate the growth mechanism of such twin InSb/GaAs nano-stripes by controlling the growth conditions, consisting of nanostructure growth duration and growth temperature. When the growth temperature is kept to less than 300°C and In deposition is set to only a few monolayers, we found that 25-40% of formed nanostructures are twin InSb/GaAs nano-stripes. However, when the In deposition is stopped immediately after the spotty reflection high-energy electron diffraction patterns are observed, the ratio of twin nano-stripes to single ones is increased to 50-60%. We therefore describe the growth mechanism of twin nano-stripes as the early state of single nano-stripe formation, where the twin nano-stripes are initially formed during the first monolayer of InSb formation as a result of large lattice mismatch of 14.6%. When In deposition is increased to a few monolayers, the gap between twin nano-stripes is filled up and consequently forms the single nano-stripes instead. With this particular twin nano-stripe growth mechanism, the preservation of high ratio of twin nano-stripe formation can be expected by further reducing the growth temperature, i.e. less than 260°C. These twin nano-stripes may find applications in the fields of spintronics and novel interference nano-devices.

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Jewasuwan, W., S. Panyakeow, and S. Ratanathammaphan. "The Formation of InP Ring-Shape Nanostructures on In_0.49Ga_0.51P Grown by Droplet Epitaxy." Advanced Materials Research 31 (November 2007): 158–60. http://dx.doi.org/10.4028/www.scientific.net/amr.31.158.

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We report on the fabrication of self-assembled InP ring-shape nanostructures on In0.49Ga0.51P by droplet molecular-beam epitaxy. The dependency of InP ring-shape nanostructural properties on substrate temperature and indium deposition rate is investigated by ex situ atomic force microscope (AFM). The nano-craters are formed when indium deposition at 120°C while the ring shape quantum-dot molecules are formed when indium deposition at 150°C or higher. The size, density and pattern of InP ring-shape nanostructures strongly depend on substrate temperature and indium deposition rate during indium deposition.

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Reznik, R. R., K. P. Kotlyar, V. O. Gridchin, I. V. Ilkiv, A. I. Khrebtov, Yu B. Samsonenko, I. P. Soshnikov, et al. "III-V nanostructures with different dimensionality on silicon." Journal of Physics: Conference Series 2103, no. 1 (November 1, 2021): 012121. http://dx.doi.org/10.1088/1742-6596/2103/1/012121.

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Abstract The possibility of AlGaAs nanowires with GaAs quantum dots and InP nanowires with InAsP quantum dots growth by molecular-beam epitaxy on silicon substrates has been demonstrated. Results of GaAs quantum dots optical properties studies have shown that these objects are sources of single photons. In case of InP nanowires with InAsP quantum dots, the results we obtained indicate that nearly 100% of coherent nanowires can be formed with high optical quality of this system on a silicon surface. The presence of a band with maximum emission intensity near 1.3 μm makes it possible to consider the given system promising for further integration of optical elements on silicon platform with fiber-optic systems. Our work, therefore, opens new prospects for integration of direct bandgap semiconductors and singlephoton sources on silicon platform for various applications in the fields of silicon photonics and quantum information technology.

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KAWAZU, T., T. NODA, T. MANO, M. JO, and H. SAKAKI. "EFFECTS OF ANTIMONY FLUX ON MORPHOLOGY AND PHOTOLUMINESCENCE SPECTRA OF GaSb QUANTUM DOTS FORMED ON GaAs BY DROPLET EPITAXY." Journal of Nonlinear Optical Physics & Materials 19, no. 04 (December 2010): 819–26. http://dx.doi.org/10.1142/s0218863510005777.

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We investigated effects of the antimony flux on GaSb quantum dots (QDs) formed by droplet epitaxy. Ga droplets were first formed on GaAs and exposed to Sb4 molecular beam at 200 °C, where the flux PSb of Sb beam was varied from 2.4 to 12.8 × 10-7 Torr. The samples were then annealed for 2 minutes under the Sb flux. An atomic microscope study showed that the diameter of GaSb QDs increases and the density decreases, as the Sb flux PSb is increased. This indicates that the coalescence process of GaSb QDs occurs and is accelerated by the increase of the Sb flux. In a photoluminescence (PL) study, we observed a broad peak of GaSb QDs in all samples, while a strong luminescence of a wetting layer (WL)-like structure was found only in the samples prepared with the high Sb flux. This suggests that the PL of WL is controllable by adjusting the flux PSb of Sb beam.

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Feddersen, Stefan, Viktoryia Zolatanosha, Ahmed Alshaikh, Dirk Reuter, and Christian Heyn. "Modeling of Masked Droplet Deposition for Site-Controlled Ga Droplets." Nanomaterials 13, no. 3 (January 23, 2023): 466. http://dx.doi.org/10.3390/nano13030466.

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Site-controlled Ga droplets on AlGaAs substrates are fabricated using area selective deposition of Ga through apertures in a mask during molecular beam epitaxy (MBE). The Ga droplets can be crystallized into GaAs quantum dots using a crystallization step under As flux. In order to model the complex process, including the masked deposition of the droplets and a reduction of their number during a thermal annealing step, a multiscale kinetic Monte Carlo (mkMC) simulation of self-assembled Ga droplet formation on AlGaAs is expanded for area-selective deposition. The simulation has only two free model parameters: the activation energy for surface diffusion and the activation energy for thermal escape of adatoms from a droplet. Simulated droplet numbers within the opening of the aperture agree quantitatively with the experimental results down to the perfect site-control, with one droplet per aperture. However, the model parameters are different compared to those of the self-assembled droplet growth. We attribute this to the presence of the mask in close proximity to the surface, which modifies the local process temperature and the As background. This approach also explains the dependence of the model parameters on the size of the aperture.

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Heyn, Christian, Leonardo Ranasinghe, Kristian Deneke, Ahmed Alshaikh, Carlos A. Duque, and Wolfgang Hansen. "Strong Electric Polarizability of Cone–Shell Quantum Structures for a Large Stark Shift, Tunable Long Exciton Lifetimes, and a Dot-to-Ring Transformation." Nanomaterials 13, no. 5 (February 25, 2023): 857. http://dx.doi.org/10.3390/nano13050857.

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Strain-free GaAs cone–shell quantum structures (CSQS) with widely tunable wave functions (WF) are fabricated using local droplet etching (LDE) during molecular beam epitaxy (MBE). During MBE, Al droplets are deposited on an AlGaAs surface, which then drill low-density (about 1 × 107 cm−2) nanoholes with adjustable shape and size. Subsequently, the holes are filled with GaAs to form CSQS, where the size can be adjusted by the amount of GaAs deposited for hole filling. An electric field is applied in growth direction to tune the WF in a CSQS. The resulting highly asymmetric exciton Stark shift is measured using micro-photoluminescence. Here, the unique shape of the CSQS allows a large charge–carrier separation and, thus, a strong Stark shift of up to more than 16 meV at a moderate field of 65 kV/cm. This corresponds to a very large polarizability of 8.6 × 10−6 eVkV −2 cm2. In combination with simulations of the exciton energy, the Stark shift data allow the determination of the CSQS size and shape. Simulations of the exciton–recombination lifetime predict an elongation up to factor of 69 for the present CSQSs, tunable by the electric field. In addition, the simulations indicate the field-induced transformation of the hole WF from a disk into a quantum ring with a tunable radius from about 10 nm up to 22.5 nm.

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Lee, Jihoon, Zh M. Wang, B. L. Liang, K. Sablon, N. W. Strom, and G. J. Salamo. "Novel Morphologies of InAs Quantum Dot Growth on GaAs Surfaces Containing Nanostructures Formed by Droplet Epitaxy." MRS Proceedings 959 (2006). http://dx.doi.org/10.1557/proc-0959-m08-02.

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ABSTRACTSelf-assembled InAs quantum dot clusters (QDCs) and InGaAs QD molecules (QDMs) have been demonstrated through a growth technique called “droplet epitaxy” by molecular beam epitaxy (MBE). For QDCs, the size and density of QDs can be controlled with variation of InAs monolayer coverages. For QDMs, Ga contribution from GaAs mound with the interaction of InAs deposition resulted in various number of InGaAs QDs per GaAs mound, ranging from 2 to 6 (bi-QDMs to hexa-QDMs) depending on the specific InAs monolayer deposition. High step density on sidewall of GaAs mound and anisotropy of surface diffusion gave a rise to preferential formation of InAs and InGaAs QDs around GaAs mounds. This hybrid growth approach combining droplet epitaxy and typical QD growth is relatively simple and flexible and doesn't require further ex-situ surface preparation. This approach of QD arrangement can find applications in optoelectronics as well as physical study of QD interaction.

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Shao, Dali, Jiang Wu, Zhenghua Li, Omar Manasreh, Vasyl P. Kunets, Zhiming M. Wang, and Gregory J. Salamo. "Quantum Ring Infrared Photodetector Based On Droplet Epitaxy Technique." MRS Proceedings 1208 (2009). http://dx.doi.org/10.1557/proc-1208-o09-24.

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AbstractIn this work, we design and fabricate a GaAs quantum ring infrared photodetector. The lattice matched GaAs/Al0.3Ga0.7As quantum rings are grown by using molecular beam epitaxy technique. The morphology of the quantum rings are characterized by an atomic force microscopy. Normal incident configured photodetectors are fabricated by standard photolithography. The photoresponse spectra are measured by a Fourier transform infrared spectrometer and exhibit two broad bands in visible-near-infrared and mid-infrared spectral range. Using quantum rings as absorption medium, we observed visible-near-infrared response at a temperature as high as 300 K while mid-infrared response up to 140 K.

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Koguchi, Nobuyuki. "Self-assembly of Semiconductor Quantum Dots by Droplet Epitaxy." MRS Proceedings 959 (2006). http://dx.doi.org/10.1557/proc-0959-m18-01.

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ABSTRACTWe have proposed a novel self-assembling growth method, termed Droplet Epitaxy, for the direct formation of QDs without using any lithography in 1990. Compared with the island formation based on the Stranski-Krastanow growth mode, the Droplet Epitaxy is applicable to the formation of quantum dots not only in lattice-mismatched but also in lattice-matched systems such as GaAs/AlGaAs. The process of the Droplet Epitaxy in MBE chamber consists of forming numerous III-column element droplets such as Ga or InGa with homogeneous size of around 10 nm on the substrate surface first by supplying their molecular beams, and then reacting the droplets with As molecular beam to produce GaAs or InGaAs epitaxial microcrystals. Another advantage of the Droplet Epitaxy is the possibility of the fabrication of QDs structures without wetting layer by cotrolling the stoichiometry of the substrate surface just before the deposition of III-column element droplets. Also we can control the shape of the QDs structure self-organizingly such as pyramidal shape, single-ring shape and concentric double-ring shape. These ring structures will provide excellent possibilities for the investigation of quantum topological phenomena.

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Wang, Yun-Ran, Im Sik Han, and Mark Hopkinson. "Fabrication of quantum dot and ring arrays by direct laser interference patterning for nanophotonics." Nanophotonics, January 10, 2023. http://dx.doi.org/10.1515/nanoph-2022-0584.

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Abstract Epitaxially grown semiconductor quantum dots (QDs) and quantum rings (QRs) have been demonstrated to be excellent sources of single photons and entangled photon pairs enabling applications within quantum photonics. The emerging field of QD-based nanophotonics requires the deterministic integration of single or multiple QD structures into photonic architectures. However, the natural inhomogeneity and spatial randomness of self-assembled QDs limit their potential, and the reliable formation of homogeneous and ordered QDs during epitaxy still presents a challenge. Here, we demonstrate the fabrication of regular arrays of single III–V QDs and QRs using molecular beam epitaxy assisted by in situ direct laser interference patterning. Both droplet epitaxy (DE) GaAs/AlGaAs QDs and QRs and Stranski–Krastanov (SK) InAs/GaAs QDs are presented. The resulting QD structures exhibit high uniformity and good optical quality, in which a record-narrow photoluminescence linewidth of ∼17 meV from patterned GaAs QD arrays is achieved. Such QD and QR arrays fabricated through this novel optical technique constitute a next-generation platform for functional nanophotonic devices and act as useful building blocks for the future quantum revolution.

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Jevasuwan, Wipakorn, Supachok Thainoi, Songphol Kanjanachuchai, Somchai Ratanathammaphan, and Somsak Panyakeow. "InAs and InP Quantum Dot Molecules and their Potentials for Photovoltaic Applications." MRS Proceedings 959 (2006). http://dx.doi.org/10.1557/proc-0959-m17-18.

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ABSTRACTSelf-assembled InAs and InP quantum dot molecules (QDMs) are grown on GaAs substrates using different molecular beam epitaxial (MBE) growth techniques. The structural and optical properties of the two types of QDMs are then compared and reported. Multi-stack high-density (1012 cm-2) InAs QDMs are grown and when inserted into GaAlAs/GaAs heterostructure results in high-efficiency solar cells. As an alternative to InAs, InP QDMs are grown by droplet epitaxy of In and annealing under P2 pressure. While the number of quantum dots per QDM in the case of InP is in the range of 10 to 12 dots, those in the case of InAs can be smaller or much larger depending on exact growth parameters prior to QD growth. Photoluminescence (PL) measurements show that while InAs QDMs provide room-temperature optical output that peaks at 1.1 eV, InP QDMs have no PL output, possibly due to crystal defects created by low-temperature processing associated with droplet epitaxy. Discussion on the practicality of our QDMs as material for intermediate band solar cells is also provided.

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Baik, Min, Ji-hoon Kyhm, Hang-Kyu Kang, Kwang-Sik Jeong, Jong Su Kim, Mann-Ho Cho, and Jin Dong Song. "Optical characteristics of type-II hexagonal-shaped GaSb quantum dots on GaAs synthesized using nanowire self-growth mechanism from Ga metal droplet." Scientific Reports 11, no. 1 (April 8, 2021). http://dx.doi.org/10.1038/s41598-021-87321-9.

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AbstractWe report the growth mechanism and optical characteristics of type-II band-aligned GaSb quantum dots (QDs) grown on GaAs using a droplet epitaxy-driven nanowire formation mechanism with molecular beam epitaxy. Using transmission electron microscopy and scanning electron microscopy images, we confirmed that the QDs, which comprised zinc-blende crystal structures with hexagonal shapes, were successfully grown through the formation of a nanowire from a Ga droplet, with reduced strain between GaAs and GaSb. Photoluminescence (PL) peaks of GaSb capped by a GaAs layer were observed at 1.11 eV, 1.26 eV, and 1.47 eV, assigned to the QDs, a wetting-like layer (WLL), and bulk GaAs, respectively, at the measurement temperature of 14 K and excitation laser power of 30 mW. The integrated PL intensity of the QDs was significantly stronger than that of the WLL, which indicated well-grown GaSb QDs on GaAs and the generation of an interlayer exciton, as shown in the power- and temperature-dependent PL spectra, respectively. In addition, time-resolved PL data showed that the GaSb QD and GaAs layers formed a self-aligned type-II band alignment; the temperature-dependent PL data exhibited a high equivalent internal quantum efficiency of 15 ± 0.2%.

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Aleknavičius, Justinas, Evelina Pozingytė, Renata Butkutė, Arūnas Krotkus, and Gintautas Tamulaitis. "Influence of laser irradiation on optical properties of GaAsBi/GaAs quantum wells." Lithuanian Journal of Physics 58, no. 1 (March 28, 2018). http://dx.doi.org/10.3952/physics.v58i1.3656.

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This paper is focused on investigation of the impact of laser irradiation on the structural and optical properties of bismide-based multiple quantum wells (MQWs). The MQW structures, composed of 5 GaAsBi quantum wells, 7 nm thick, separated by 10 nm-thick GaAs barriers, were grown by molecular beam epitaxy on GaAs (100)-plane oriented semi-insulating substrates at 330°C temperature. The bismuth content in as-grown GaAsBi wells evaluated from the measurements of HR-XRD rocking curves was about 6%. HR-TEM and AFM studies of the MQWs evidenced sharp interfaces between the wells and barriers, and a smooth, droplet-free surface, respectively. HR-TEM images also evidenced a homogeneous bismuth distribution in the wells. The spatially-resolved photoluminescence study of GaAsBi/GaAs MQWs revealed the enhancement of PL emission efficiency of up to 80% with no shift of the spectral position after intense laser irradiation. The obtained results were explained by improvement of the GaAsBi crystal quality.

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Stoleru, Valeria Gabriela, Elias Towe, Chaoying Ni, and Debdas Pal. "Quantum-Dot Molecules for Potential Applications in Terahertz Devices." MRS Proceedings 829 (2004). http://dx.doi.org/10.1557/proc-829-b1.3.

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ABSTRACTThe experimental and theoretical results of the electronic and optical properties of quantum dot artificial molecules (AMs), formed by pairs of electronically coupled quantum dots (QDs), are presented here in order to identify the necessary conditions for the development of new types of terahertz (THz) injection lasers based on intraband carrier transitions. We have performed analytical calculations to obtain the spatial strain distribution in vertically aligned (In, Ga)As QDs grown on (001) GaAs substrates by molecular beam epitaxy. Electronic coupling of the dots, mainly governed by the thickness of the separating barrier between the dot layers, is allowed due to the strain field-assisted self-organization of the dots. The calculated strain field reproduces our cross sectional high-resolution transmission electron microscopy observations very well. We further take into account the microscopic effects of the spatial strain distribution on carrier confinement potentials, and compute the electronic structure of the AM. Our calculations of the peak luminescence energies are in good agreement with our experimental results and those of others. The growth of quantum dot molecules represents a major step in tailoring the electronic and optical properties of the nanostructures.

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Tenne, D. A., A. G. Milekhin, A. K. Bakarov, O. R. Bajutova, V. A. Haisler, A. I. Toropov, S. Schulze, and D. R. T. Zahn. "Raman spectroscopy of self-assembled InAs quantum dots in wide-bandgap matrices of AlAs and aluminium oxide." MRS Proceedings 737 (2002). http://dx.doi.org/10.1557/proc-737-e13.8.

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ABSTRACTVibrational properties of self-assembled InAs quantum dots (QD’s) embedded in AlAs and aluminium oxide were studied by Raman spectroscopy. The InAs/AlAs QD structures were grown by molecular beam epitaxy on GaAs (001) substrates. The following main features of the phonon spectra of InAs/AlAs QD nanostructures were observed: 1) asymmetric lines of QD LO phonons affected by strain, confinement and size inhomogeneity of QD’s; 2) confined phonons of InAs wetting layer (WL); 3) two bands of interface phonons in the AlAs frequency region, attributed to modes associated with the planar interface WL/AlAs matrix and the three-dimensional QD/matrix interface; 4) doublets of folded acoustic phonons caused by periodicity in the multilayer QD structures. The influence of growth temperature, varied from 420 to 550°C, on the morphology of QD’s was investigated. QD’s grown at 420°C are found to have the smallest size. Increasing the temperature up to 480°C leads to the formation of larger InAs islands and improved size homogeneity. Further temperature elevation (above 500°C) causes partial re-evaporation of InAs leading to a decrease of QD size and density, and, finally, their complete disappearance. InAs QD’s embedded in aluminium oxide were fabricated by selective oxidation of the AlAs matrix in self-assembled InAs/AlAs QD’s. Micro-Raman spectroscopy data show that depending on oxidation conditions (humidity, temperature) InAs QD’s in an oxide matrix can be even more strained than before oxidation, or become fully relaxed. At the boundaries of oxidized/non-oxidized areas the presence of amorphous and crystalline As clusters is evident.

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Journal articles on the topic 'GaAs, quantum nanostructures, molecular beam epitaxy, droplet epitaxy'

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