InAs Nanostructures Research Articles

Effect of strain compensation and growth interruption on the morphology of InAs nanostructures grown on InAs/InAlGaAs/InP

利用固源分子束外延(Molecular Beam Epitaxy, MBE)设备生长出InAs/InAlGaAs/InP(001)纳米结构材料, 探讨了应变补偿技术和生长停顿对InAs 纳米结构形貌的影响. 应变补偿技术的引入导致量子点和量子线混合结构的形成, 有望成为超宽带半导体激光器的有源区; 生长InAs 时生长停顿的引入导致尺寸分布均匀的量子线结构的形成, 可作为单色激光器有源区.

Optical techniques for pump-probe magnetic measurements and nanoimaging of biological samples

Fast pump-probe magneto-optic techniques have been used to investigate the hot carrier and magnetization dynamics in InAs nanostructures deposited on GaAs(001). From these time resolved reflectivity and Faraday rotation measurements, different dynamics responses were found for samples containing different InAs thicknesses. We also present some results of near field spectroscopy with infrared radiation emitted by a free electron laser to investigate biological samples. The local reflectivity revealed features as a function of photon energy that were not present in the corresponding shear-force (topology) images and were due to localized changes in the bulk properties of the sample.

Optical and microstructural properties of self-assembled InAs quantum structures in silicon

Abstract The InAs quantum structures were formed in silicon by sequential ion implantation and subsequent thermal annealing. Two kinds of crystalline InAs nanostructures were successfully synthesized: nanodots (NDs) and nanopyramids (NPs). The peaks at 215 and 235 cm−1, corresponding to the transverse optical (TO) and longitudinal optical (LO) InAs single-phonon modes, respectively, are clearly visible in the Raman spectra. Moreover, the PL band at around 1.3 µm, due to light emission from InAs NDs with an average diameter 7±2 nm, was observed. The InAs NPs were found only in samples annealed for 20 ms at temperatures ranging from 1000 up to 1200°C. The crystallinity and pyramidal shape of InAs quantum structures were confirmed by HRTEM and XRD techniques. The average size of the NPs is 50 nm base and 50 nm height, and they are oriented parallel to the Si (001) planes. The lattice parameter of the NPs increases from 6.051 to 6.055 Å with the annealing temperature increasing from 1100 to 1200°C, due to lattice relaxation. Energy dispersive spectroscopy (EDS) shows almost stoichiometric composition of the InAs NPs.

Long-wavelength, confined optical phonons in InAs nanowires probed by Raman spectroscopy

Strongly confined nano-systems, such as one-dimensional nanowires, feature deviations in their structural, electronic and optical properties from the corresponding bulk. In this work, we investigate the behavior of long-wavelength, optical phonons in vertical arrays of InAs nanowires by Raman spectroscopy. We attribute the main changes in the spectral features to thermal anharmonicity, due to temperature effects, and rule out the contribution of quantum confinement and Fano resonances. We also observe the appearance of surface optical modes, whose details allow for a quantitative, independent estimation of the nanowire diameter. The results shed light onto the mechanisms of lineshape change in low-dimensional InAs nanostructures, and are useful to help tailoring their electronic and vibrational properties for novel functionalities.

Anomalous Temperature Dependence of Photoluminescence in InAs/InAlGaAs/InP Quantum Wire and Dot Hybrid Nanostructures

Self-assembled InAs quantum wires (QWRs) are fabricated on an InP substrate by solid-source molecular beam epitaxy (SSMBE). Photoluminescence (PL) spectra are investigated in these nanostructures as a function of temperature. An anomalous enhancement of PL intensity and a temperature insensitive PL emission are observed from InAs nanostructures grown on InP substrates using InAlGaAs as the matrix layer and the origin of this phenomenon is discussed. We attribute the anomalous temperature dependence of photoluminescence to the formation of Al-rich and In-rich region in the InAlGaAs buffer layer and the cap layer.

Piezoelectric InAs (211)B quantum dots grown by molecular beam epitaxy: Structural and optical properties

The structural and optical properties of piezoelectric (211)B InAs nanostructures grown by molecular beam epitaxy are systematically investigated as a function of the various growth parameters. Depending on the specific growth conditions, we show that the InAs nanostructures take the form of a quantum dot (QD) or a quantum dash, their height ranges between 2 and 20 nm, and their density varies from a few times 108 cm−2 all the way up to a few times 1010 cm−2. The (211)B QDs are characterized by large aspect ratios, which are compatible with a truncated pyramid morphology. By analyzing the QD emission spectrum, we conclude that only small size QDs, with heights less than 3 nm, are optically active. This is consistent with high resolution transmission electron microscopy observations showing that large QDs contain misfit dislocations, whereas small QDs are dislocation-free. The formation of a two-dimensional wetting layer is observed optically, and its thickness is determined to be between 0.30 and 0.39 nm. Finally, the large blueshift in the QD emission observed with increasing excitation power represents a clear evidence of the strong built-in piezoelectric field present in these dots.

Structural Stability and Electronic Properties of InAs Nanowires and Nanotubes: Effects of Surface and Size

The surface and size effects on the structural stability and electronic properties of InAs one-dimensional nanostructures are investigated by first-principles calculations within density functional theory. No matter what the diameters, the nanowires are more energetically favorable than the nanotubes due to the preferable sp3 hybridization for In and As atoms in the InAs nanostructures. The formation energies of these nanostructures satisfy a linear dependence relationship with the surface atom ratio. The calculated band structures reveal that the band gaps of InAs nanostructures are determined by two competition mechanisms. One is the quantum confinement effect, which favors the increase of the band gaps with the decreasing diameter or wall thickness. Another is the effect of surface dangling bonds, which induces the decrease of the band gaps with the decreasing diameter or wall thickness. With the same diameter, the band gaps of InAs nanowires are still less than those of the nanotubes. The result indicates that the quantum confinement effect in one-dimensional structures can be enhanced by the formation of tubes instead of wires.

InAs nanostructures on InGaAsP/InP(001): Interaction of InAs quantum-dash formation with InGaAsP decomposition

Cross-sectional scanning tunneling microscopy is used to study the spatial structure and composition of self-assembled InAs nanostructures grown on InGaAsP lattice matched to the InP substrate. Images of the (110) and (1¯10) cleavage surfaces reveal InAs quantum dashes of different lateral extensions. They are found to be about 60 nm long, about 15 nm wide, about 2 nm high, and to consist of pure InAs. Furthermore, the quaternary InGaAsP matrix material below, in between, and above the quantum-dash layers shows a strong lateral contrast variation, which is related to a partial decomposition into columns of more InAs-rich and more GaP-rich regions. The effect is particularly pronounced along the [110] direction. A quantitative analysis of this strain-induced contrast yields a decomposition characterized by variations of the group-III and/or group-V concentrations in the order of ±10%. The data strongly indicate that the strain at the growth surface induced by the decomposition of the underlying matrix material plays an important role for the nucleation and formation of the quantum dashes as well as for their unexpected stacking over interlayer distances as large as 40 nm. Despite of the observation that the quantum dashes enforce the decomposition, which was already developed directly at the InGaAsP/InP interface without any influence of the subsequently grown InAs quantum dashes.

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.

Photoluminescence and photoreflectance studies of InAs self-assembled nanostructures on GaAs(631) substrates

The authors report the photoluminescence and photoreflectance characteristics of molecular beam epitaxy grown InAs nanostructures on GaAs (631)-oriented substrates. Prior to the InAs growth, self-assembled nanochannels on the GaAs buffer layer were formed, which later were used as templates for nanostructures formation. Different samples were prepared by varying the amount of InAs from 0.75 to 2 ML (monolayer), 50 nm of GaAs was grown on top as a capping layer. Low temperature photoluminescence spectroscopy showed intense optical transitions in the spectra, their energy position directly depends on the quantity of InAs deposited. The self-assembling of InAs quantum wires (QWRs) at the early stages of growth is suggested. Anisotropy effects in the InAs nanostructures were corroborated by polarized photoluminescence supporting the proposal of formation of QWRs. Photoreflectance spectroscopy at room temperature was also employed to characterize the samples. It is found that in addition to the band-gap energy transition, features associated with quantum confinement in the wetting layer were observed even for very low quantities of InAs deposited.

Investigation of a contacting scheme for self-assembled cleaved edge overgrown InAs nanowires and quantum dot arrays

The expanding of research in nano-scale systems is essentially driven by interest in the fun-damental physical properties of solid state matter at the nanoscale and the hope to apply them to novel technologi-cal devices. With self-assembled (bottom-up approach) nanostructures it is possible to achieve even smaller sized structures in combination with top-down technologies and allow at the same time a high control of the size distribu-tion. An example for such materials are defect free semi-conductor QDs grown by MBE or CVD processes [1]. Es-pecially III–V self-assembled QDs, e.g. InGaAs QDs, are subject to intense investigations due to their superior opti-cal properties. These systems are interesting due to promis-ing applications, like single photon sources, lasing, optical amplifiers or solar cells [2–4]. For this reason it is interest-ing to characterize the electronic properties of self-assembled nanostructures. Ensembles of QDs can be con-tacted by embedding the QDs film into a pin-diode struc-ture. However to address single or a small ensemble of nanostructures still represents a challenging task. In several previous publications the promising approach of self-assembled InAs nanostructures obtained by cleaved edge overgrowth was presented [5, 6]. Again the optical proper-ties are easily accessible [7], but for further investigations a direct injection of charge carriers into the nanostructures is interesting. Previous pioneering work has shown how CEO structures can be used for low-dimensional transport at the cleavage plane first in GaAs quantum wires [8] and more recently in AlAs quantum wires [9]. At this point we would like to shortly review the technique of self-assembled InAs nanostructure growth. The procedure re-lies on the fact that the three-dimensional InAs layer

Modulation spectroscopy of InAs semiconductor nanostructures grown on (631) high index substrates

AbstractThe molecular beam epitaxial (MBE) growth of InAs nanostructures on GaAs(631)‐oriented substrates is studied by photoluminescence (PL) and photoreflectance spectroscopy (PR). First, a corrugated surface conformed by regularly spaced grooves aligned along the [$ \bar 5 $93] azimuth was formed by the GaAs homoepitaxial growth on the (631) substrate. On this template, we proceeded with the deposition of InAs at several thicknesses in the range of 1 to 4.5 monolayers (MLs). An atomic force microscopy (AFM) analysis of samples without GaAs capping, revealed that assemblage of QDs occurs only after the deposition of the equivalent to ∼1.9 ML of InAs. On these samples, we observed changes on the PR line‐shape in the near‐bandgap GaAs region linked to the quantity of InAs deposited. The intensity of the built in electric fields was correlated with the strain state at the heterointerface, as a consequence of the self induced piezoelectric effect, typical from high index surfaces. On the other hand, when the samples were capped with a 100 Å thick GaAs layer, strong emission of the nanostructures occurs even for deposited quantities of InAs as low as 1 ML. Since for this InAs thickness the self‐assemblage of QDs is not observed, the optical transitions observed were associated with the optical emission of self assembled semiconductor quantum wires, promoted by surface diffusion anisotropy, characteristic of the (631) plane. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InAs nanostructures on polar GaAs surfaces

InAs nanostructures were grown by molecular beam epitaxy on GaAs (111)B and (211)B substrates at various growth temperatures between 450°C and 530°C. Their structural properties were studied by atomic force microscopy. For the (111)B grown nanostructures, the formation of self-aligned InAs quantum dashes was revealed, which in some cases took the form of nanowires. In the (211)B case, the shape and size of nanostructures is drastically affected by growth temperature. At lower growth temperatures, fabrication of quantum dots has been achieved by deposition of 2MLs of InAs. However, when the same amount of InAs was deposited at higher growth temperatures, a drastic change of nanostructure from dots to dashes occurred. Towards a better understanding of nanostructure properties, systematic photoluminescence (PL) measurements were performed on the (211) sample series. No PL emission related to quantum dash formation was observed, while a PL peak position at 1.27 eV was attributed to the (211)B InAs dots grown at 500°C. The PL peak blueshifted upon increasing the excitation intensity, an effect suggested to be related with the existence of strong piezoelectric field in the [211]B direction. The latter was also confirmed in micro-PL experiments through metallic apertures, where a negative biexciton binding energy was observed.

InGaAs quantum wires grown on (1 0 0)InP substrates

We have investigated the growth of InGaAs wires on InP substrates by tuning the Ga composition. Nanostructures including InAs, In 0.95Ga 0.05As, In 0.90Ga 0.10As, and In 0.85Ga 0.15As were grown on In 0.53Ga 0.26Al 0.21As buffer layers. For the growth of InAs nanostructures, elliptical quantum dots are observed. As we add Ga composition to the nanostructures, quantum wires arrays along the [0 1¯ 1] direction are formed for In 0.95Ga 0.05As and In 0.90Ga 0.10As nanostructures, and the In 0.85Ga 0.15As nanostructure shows a dash-wire morphology. The In 0.90Ga 0.10As quantum wires have a photoluminescence spectrum of emission peak at λ ∼ 1680 nm and a narrow full-width at half-maximum of 65 meV at 10 K. The In 0.90Ga 0.10As quantum wires show a high emission polarization anisotropy of 47%.

InAs/GaAs nanostructures grown on patterned Si(001) by molecular beam epitaxy

The potential benefit from the combination of the optoelectronic and electronicfunctionality of III–V semiconductors with silicon technology is one of the most desiredoutcomes to date. Here we have systematically investigated the optical properties ofInAs quantum structure embedded in GaAs grown on patterned sub-micron andnanosize holes on Si(001). III–V material tends to accumulate in the patternedsub-micron holes and a material depletion region is observed around holes whenGaAs/InAs/GaAs is deposited directly on patterned Si(001). By use of a 60 nmSiO2 layer and patterning sub-micron and nanosize holes through the oxide layer to thesubstrate, we demonstrate that high optical quality InAs nanostructures, both quantumdots and quantum wells, formed by a two-monolayer InAs layer embedded inGaAs can be epitaxially grown on Si(001). We also report the power-dependentand temperature-dependent photoluminescence spectra of these structures. Theresults show that hole diameter (sub-micron versus nanosize) has a strong effecton the structural and optical properties of GaAs/InAs/GaAs nanostructures.

Controlled synthesis of InAs wires, dot and twin-dot array configurations by cleaved edgeovergrowth

We present experimental results on the controlled synthesis of InAs ordered nanostructureswith three different grades of complexity: nanowires, quantum dot arrays, and doublequantum dot arrays. A model for the diffusion of In adatoms on (110) surfaces explains theobserved ordering and establishes general criteria for the optimized fabrication of the threedifferent InAs nanostructure configurations, as a function of the growth conditions. Theseresults are important for the use of ordered InAs nanostructures in future optoelectronicapplications.

Effect of thickness on the self-positioning of nanostructures

Atomic-scale modeling of self-positioning GaAs–InAs nanostructures is performed. Curvature radius values obtained by the atomic-scale finite element method are compared with those obtained by a continuum mechanics solution under plane strain conditions. Atomic-scale modeling and continuum mechanics solution predict the same curvature radius for structures with large thickness. However, atomic-scale modeling shows significant decrease of the curvature radius for structures with thickness less than 40nm.

InAs nanostructures on InP (001) substrate with the insertion of a superthin AlAs layer

An AlAs layer of two or three monolayers was inserted beneath the strained InAs layer in the fabrication of InAs nanostructure on the In0.53Ga0.47As and In0.52Al0.48As buffer layer lattice-matched to InP(001) substrate using molecular beam epitaxy. The effects of AlAs insertion on the InAs nanostructures were investigated and discussed.

Electron field emission from narrow band gap semiconductors (InAs)

We propose to use InAs for the development of effective electron field emitters on the basis of a new technological approach for the preparation of highly textured surfaces which allows one to obtain peculiar fine rod-like micro- and nanostructures. A decrease of the current–voltage characteristics slope by a factor of 3.5 was observed in the Fowler–Nordheim plot with increasing applied voltage. This significant change in the slope is discussed on the basis of two different mechanisms: the inter-valley hot carrier redistribution and the existence of two arrays of nanocathodes with different radii of the top. The developed InAs nanostructures may also find applications in IR-sensitive displays, submicron sources of irradiation and devices with variable bands and barriers.

Growth of InAs nanostructures on InP using atomic-force nanolithography

Atomic-force nanolithography was used to control the nucleation sites of InAs nanostructures on InP substrates. Indentations with a wide range of dimensions were produced on InP. InAs nanostructures were selectively grown by metal organic vapor phase epitaxy. It is shown that the number of active nucleation sites depends on the normal force applied during nanoindentation. Crystalline defects introduced by nanoindentation are shown to be nucleation sites for these nanostructures. The presence of screw dislocations within the grown nanostructures further supports this observation.