共查询到20条相似文献,搜索用时 10 毫秒
1.
Z.Y. Zhang C.L. YangY.Q. Wei X.L. YeP. Jin Ch.M. LiX.Q. Meng B. XuZ.G. Wang 《Solid State Communications》2003,126(7):391-394
In this report we have investigated the temperature dependence of photoluminescence (PL) from self-assembled InAs quantum dots (QDs) covered by an InAlAs/InGaAs combination layer. The ground state experiences an abnormal variation of PL linewidth from 15 K up to room temperature. Meanwhile, the PL integrated intensity ratio of the first excited state to the ground state for InAs QDs unexpectedly decreases with increasing temperature, which we attribute to the phonon bottleneck effect. We believe that these experimental results are closely related to the partially coupled quantum dots system and the large energy separation between the ground and the first excited states. 相似文献
2.
An InAs ring structure accompanying the formation of quantum dots (QDs) was fabricated on (1 0 0)GaAs using droplet epitaxy. The QDs were located in the vicinity of the ring, due to the diffusion of In atoms from the In droplets. In addition, the dots were found to have distributed elliptically and preferentially along the [0 1 1] direction, implying that In itself prefers to diffuse along the [0 1 1] direction, which is the opposite of the favorable diffusion orientation of group III atoms on (1 0 0)GaAs under a commonly used As-stabilized growth condition. This is the first observation of a ring structure accompanying the formation of quantum dots in droplet epitaxy. 相似文献
3.
Formation of a multimodal quantum dot (QD) ensemble by strained layer epitaxy of InAs on GaAs near the critical value for the onset of the 2D-3D transition is studied. Reflection anisotropy spectroscopy is employed to confirm that a smooth surface is maintained during strained layer growth prior to QD formation. Instantaneous capping after deposition leads to InAs quantum wells with some thickness flucuations. Multimodal QD InAs ensembles form after an at least short growth interruption prior to cap layer deposition. The QDs consist of pure InAs with heights varying in steps of complete InAs monolayers. Related exciton energies indicate a simultaneous increase of both height and lateral extension, i.e. a shell-like increase of sizes. The formation of the multimodal QD ensemble is described by a kinetic approach. A growth scenario is presented where QDs having initially shorter base length stop vertical growth at a smaller height, accounting for the experimentally observed shell-like sub-ensemble structure. 相似文献
4.
Reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) measurements were used to investigate the dependences of the formation process and the strain on the As/In ratio and the substrate temperature of InAs quantum dots (QDs) grown on GaAs substrates by using molecular beam epitaxy. The thickness of the InAs wetting layer and the shape and the size of the InAs QDs were significantly affected by the As/In ratio and the substrate temperature. The strains in the InAs layer and the GaAs substrate were studied by using RHEED patterns. The magnitude in strain of the InAs QDs formed at a low substrate temperature was larger than that in InAs QDs grown at high substrate temperature. The present results can help to improve the understanding of the formation process and the strain effect in InAs QDs. 相似文献
5.
InAs quantum dots (QDs) were grown by molecular beam epitaxy in the Stranski-Krastanow growth mode. The samples were placed between two undoped GaAs slices and annealed in nitrogen ambient at different temperature. Effect of annealing temperature on the evolution of QDs morphology is investigated by the AFM. This behavior can be attributed to the mechanisms of QDs ripening, intermixing and segregation in the annealing process. A number of QDs have evoluted into the uniform distribution quantum rings (QRs) when the sample was annealed at the temperature of 800 °C. The results indicated that high density and uniform QRs can be obtained by the post-growth technique. 相似文献
6.
K.D. Moiseev Ya.P. Parkhomenko E.A. Gushchina S.S. Kizhaev M.P. Mikhailova 《Applied Surface Science》2009,256(2):435-437
We report a study of InSb nanoobjects (quantum dots and quantum rings) grown on InAs-rich surface by liquid phase epitaxy. Characterization of the sample surface was performed using atomic force microscopy (AFM). The bimodal formation of the uncapped InSb quantum dots (QDs) was observed for the growing on a binary InAs substrate. Uniform high-density (1 × 1010 cm−2) quantum dots with a height of 3 nm were obtained at T = 420-430 °C, whereas low-density (5 × 108 cm−2) big quantum dots were 9 nm in height. As a buffer layer, lattice-matched InAsSb0.12P0.25 solid solution was deposed on InAs substrate using metal-organic vapour phase epitaxy. Deposition from the InSb melt on the buffer layer resulted in the formation of InSb nanoobjects with density as high as 3 × 1010 cm−2. 相似文献
7.
The electrical and the optical properties of InAs/GaAs quantum dots (QDs) grown by using atomic layer epitaxy (ALE) technique were investigated by using capacitance-voltage (C-V) and photoluminescence (PL) measurements. C-V curves showed that the plateaus related to the zero-dimensional carrier confinement effect existed and that the number of electrons occupying the InAs QD was approximately 7. The full width at half maxima of the interband transitions from the ground electronic subband to the ground heavy-hole subband and from the first excited electronic state to the first excited state heavy-hole subband were not significantly affected by the temperature variation, indicative of strong confinement of the carriers occupying the InAs QDs. These results can help improve understanding for applications of InAs/GaAs QDs grown by using ALE in high-efficiency electronic and optoelectronic devices. 相似文献
8.
The effect of thermal annealing on self-assembled uncapped InAs/GaAs quantum dots (QDs) has been investigated using transmission electron microscopy (TEM) and photoluminescence (PL) measurements. The TEM images showed that the lateral sizes and densities of the InAs QDs were not changed significantly up to 650 °C. When the InAs/GaAs QDs were annealed at 700 °C, while the lateral size of the InAs QDs increased, their density decreased. The InAs QDs disappeared at 800 °C. PL spectra showed that the peaks corresponding to the interband transitions of the InAs QDs shifted slightly toward the high-energy side, and the PL intensity decreased with increasing annealing temperature. These results indicate that the microstructural and the optical properties of self-assembled uncapped InAs/GaAs can be modified due to postgrowth thermal annealing. 相似文献
9.
A. Aierken T. Hakkarainen M. Sopanen J. Riikonen J. Sormunen M. Mattila H. Lipsanen 《Applied Surface Science》2008,254(7):2072-2076
Formation of self-assembled InAs 3D islands on GaAs (1 1 0) substrate by metal organic vapor phase epitaxy has been investigated. Relatively uniform InAs islands with an average areal density of 109 cm−2are formed at 400 ° C using a thin InGaAs strain reducing (SR) layer. No island formation is observed without the SR layer. Island growth on GaAs (1 1 0) is found to require a significantly lower growth temperature compared to the more conventional growth on GaAs (1 0 0) substrates. In addition, the island height is observed to depend only weakly on the growth temperature and to be almost independent of the V/III ratio and growth rate. Low-temperature photoluminescence at 1.22 eV is obtained from the overgrown islands. 相似文献
10.
Low Density Self-Assembled InAs/GaAs Quantum Dots Grown by Metal Organic Chemical Vapour Deposition
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The self-assembled InAs quantum dots (QDs) on GaAs substrates with low density (5×10^8 cm^-2) are achieved using relatively higher growth temperature and low InAs coverage by low-pressure metal-organic chemical vapour deposition. The macro-PL spectra exhibit three emission peaks at 1361, 1280 and 1204nm, corresponding to the ground level (GS), the first excited state (ES1) and the second excited state (ES2) of the QDs, respectively, which are obtained when the GaAs capping layer is grown using triethylgallium and tertiallybutylarsine. As a result of micro-PL, only a few peaks from individual dots have been observed. The exciton-biexciton behaviour was clearly observed at low temperature. 相似文献
11.
We have fabricated a Schottky diode embedding InAs self-assembled quantum dots (QDs) grown by alternately supplying In and As sources. As a function of the electric field, we have investigated the photoluminescence (PL) for the InAs QDs in the Schottky diode at 300 K. We controlled the electric field in order that the QD layer was located in the depletion region of Schottky diode. The relationship between the electric field and the depletion width of the Schottky diode was deduced through the capacitance-voltage measurement. The Stark shift was observed in PL spectra for QDs; the energy of the PL line shifted to the lower energy as the electric field increased. It was also observed that the PL emission intensity gradually decreased. By the fitting to the experimental data, we determined a built-in dipole moment, corresponding to an electron-hole separation. 相似文献
12.
M. Rusanen I. T. Koponen T. Ala-Nissila 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):405-409
A reaction kinetic model is proposed for height selection of heteroepitaxially growing
nanometer-thick quantum dots. The model describes the growth by a set of
rate equations for the combined size and height
distributions of the dots. In addition to nucleation and growth,
the model includes a coarse-grained conversion rate incorporating
kinetics of height changes. With suitably chosen rate coefficients
the model reproduces qualitatively the experimentally
observed height-selected size distributions and their evolution.
The results support the view that
the height selection and the form of the size distribution both result from
the oscillating energy barrier for the transformation of dots of different heights,
and this transformation barrier
is considerably larger in magnitude than
oscillations in the electronic energy due to quantum well states
in the dot. 相似文献
13.
M. V. Dorokhin A. V. Zdoroveishev E. I. Malysheva Yu. A. Danilov B. N. Zvonkov A. E. Sholina 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(3):511-514
A self-organized InAs/GaAs quantum dot (QD) array is doped with Mn. The effect of the Mn concentration on the morphology and QD luminescence properties is investigated. It is found that Mn deltadoping of the GaAs buffer layer before QD growth with a layer concentration of 1014 cm?2 leads to the formation of an array of large QDs with variable composition In x Ga1 ? x As. The effect is explained within a model of In and Ga atom interdiffusion. 相似文献
14.
Self-assembled InAs quantum dots (QDs) with high-density were grown on GaAs(0 0 1) substrates by antimony (Sb)-mediated molecular beam epitaxy technique using GaAsSb/GaAs buffer layer and InAsSb wetting layer (WL). In this Sb-mediated growth, many two-dimensional (2D) small islands were formed on those WL surfaces. These 2D islands provide high step density and suppress surface migration. As the results, high-density InAs QDs were achieved, and photoluminescence (PL) intensity increased. Furthermore, by introducing GaAsSb capping layer (CL), higher PL intensity at room temperature was obtained as compared with that InGaAs CL. 相似文献
15.
K. A. Nevalainen M. Rusanen I. T. Koponen 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(4):311-322
The size selection of nanodots during the growth is studied by using a reaction kinetic model, where reaction rates depend
on the dot size.
The characteristic feature of the reaction rates is the energetics, where the free energy of dots has a minimum at the certain
dot size.
The model equations are solved by using a particle coalescence simulation method. We find phenomenologically three distinct
stages of growth. First, during the initial deposition stage, distributions with high density of small dots occur. Second,
there is an intermediate and short-lived stationary state, which is controlled by kinetics of growth. Third, a long-lived
stationary state is obtained, with nearly Gaussian size distributions, mostly determined by the energetics of the growth but
also significantly affected by the kinetics. In the final stage, size selection and narrowing of the distributions occur.
It is also shown that in the final stage of growth the Fokker-Planck type continuum model describes well the evolution of
the distributions and the size selection. 相似文献
16.
A. P. Gorshkov N. S. Volkova I. A. Karpovich A. V. Zdoroveishev I. A. Polova 《Bulletin of the Russian Academy of Sciences: Physics》2013,77(1):53-55
Study of the shape of the photoelectric spectrum from InAs/GaAs quantum dots and its temperature dependence is shown to be capable of revealing bimodal arrays of quantum dots. 相似文献
17.
Temperature Insensitivity of Optical Properties of InAs/GaAs Quantum Dots due to a Pregrown InGaAs Quantum Well
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Both the peak position and linewidth in the photoluminescence spectrum of the InAs/GaAs quantum dots usually vary in an anomalous way with increasing temperature. Such anomalous optical behaviour is eliminated by inserting an In0.2Ga0.8As quantum well below the quantum dot layer in molecular beam epitaxy. The insensitivity of the photoluminescence spectra to temperature is explained in terms of the effective carrier redistribution between quantum dots through the In0.2Ga0.8As quantum well. 相似文献
18.
F. Frost 《Applied Physics A: Materials Science & Processing》2002,74(1):131-133
Starting from a theory recently proposed by Kahng et al. that explains the formation of ordered dots by ion sputtering under
normal ion incidence, it was demonstrated that extending this theory to ion sputtering under oblique ion incidence with simultaneous
sample rotation offers the self-organized formation of dots by ion sputtering for a large variety of different ion/material
combinations. While for sputtering under normal incidence the shape of the collision cascade must be anisotropic, where the
lateral straggling exceeds the longitudinal straggling, this constraint is not necessary under oblique incidence.
Received: 16 May 2001 / Accepted: 10 September 2001 / Published online: 17 October 2001 相似文献
19.
We investigate the molecular beam epitaxy growth of metamorphic InxGal-xAs materials (x up to 0.5) on GaAs substrates systematically. Optimization of structure design and growth parameters is aimed at obtaining smooth surface and high optical qualdty. The optimized structures have an average surface roughness of 0.9-1.8 nm. It is also proven by PL measurements that the optical properties of high indium content (55%) InGaAs quantum wells are improved apparently by defect reduction technique and by introducing Sb as a surfactant. These provide us new ways for growing device quality metamorphic structures on GaAs substrates with long-wavelength emissions. 相似文献
20.
C2H4 mediations were used to modify the Stranski-Krastanow growth mode of Ge dots on Si(0 0 1) at 550 °C by ultra-high vacuum chemical vapor deposition. With appropriate C2H4-mediation to modify the Si surface, the elongated Ge hut clusters can be transformed to highly uniform Ge domes with a high Ge composition at the core. These C2H4-mediated Ge dots, almost bounded by {1 1 3} facets, have an average diameter and height of 55 and 9 nm, respectively. We propose two major mechanisms to depict the formation of these C2H4-mediated Ge dots: (i) an almost hydrogen-passivated Si surface to limit the nucleation sites for dot formation, and (ii) the incorporation of Ge atoms, repelled by the C-rich areas, into the existing Ge dots. This work provides a useful scheme to tune the topography of Ge dots in an UHV/CVD condition for possible optoelectronic applications. 相似文献