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  • Articles  (14)
  • American Institute of Physics (AIP)  (14)
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  • Articles  (14)
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  • 1
    Electronic Resource
    Electronic Resource
    On the origin of the "coffee-bean" contrast in transmission electron microscopy images of CdSe/ZnSe quantum dot structures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4150-4155 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origin of the "coffee-bean" strain contrast is studied, that is observed in the plan-view transmission electron microscopy (TEM) images of CdSe/ZnSe quantum dot structures. The samples were grown by two different methods: standard molecular-beam epitaxy at 350 °C and atomic layer epitaxy at 230 °C with annealing at 340 °C after the CdSe deposition. The nominal CdSe thickness was above 3 ML. In situ reflection high energy electron diffraction during the growth or during the annealing shows the transition from the two- (2D) into the three-dimensional (3D) surface morphology for both samples. The coffee-bean contrast is usually assigned to three-dimensional islands which are generated after the morphological 2D/3D transition. It is found that the coffee-bean contrast in plan-view TEM images is alternatively associated with pairs of stacking faults on {111} lattice planes which are inclined against each other. The stacking faults, which are bound by Shockley partial dislocations, are preferably generated in the vicinity of the Cd-rich regions (large islands) of the CdZnSe layer where Cd concentrations of more than 40% are found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352028
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  • 2
    Electronic Resource
    Electronic Resource
    Growth and vertical correlation of CdSe/ZnSe quantum dots (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 3695-3699 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The growth and vertical organization of CdSe quantum dots in three-layer stacks consisting of CdSe with a nominal thickness of 2.5 monolayers (ML) and ZnSe spacers with thicknesses between 10 and 20 ML was investigated by reflection high energy electron diffraction during the growth and different transmission electron microscopy techniques. The samples were grown by molecular beam epitaxy at 400 °C. It was found that up to 10 ML spacer thickness all three CdSe layers and ZnSe spacers form one broad (Cd, Zn)Se alloy layer with a small Cd concentration containing Cd-rich islands with a size of ∼15 nm. For spacers with a larger thickness (12–20 ML) three separated ternary (Cd, Zn)Se layers are observed which contain Cd-rich inclusions (small islands) with a size of less than 10 nm. A preferential vertical correlation of the small islands occurs for the 12 ML spacer thickness. With increasing spacer thickness, the number of the correlated small islands is reduced displaying a tendency to uncorrelated growth. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352676
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of the growth procedure on the Cd distribution in CdSe/ZnSe heterostructures: Stranski–Krastanov versus two-dimensional islands (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 640-642 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Molecular beam epitaxy is used to grow different types of ZnSe/CdSe/ZnSe heterostructures. The topography of the bare CdSe surface studied with in situ atomic force microscopy is compared with high-resolution transmission electron microscopy data on overgrown structures. The growth procedure critically influences morphology and Cd distribution. Only use of thermal activation after low-temperature CdSe deposition enables the accomplishment of a distinct Stranski–Krastanov (SK) morphology with three-dimensional islands with a core of pure CdSe. Interdiffusion effects during activation of the SK transition as well as overgrowth are of minor importance. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1496133
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  • 4
    Electronic Resource
    Electronic Resource
    Structural properties of CdMgTe/CdTe superlattices (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7323-7329 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CdMgTe/CdTe superlattices with a high degree of structural perfection were grown on CdTe and Cd0.975Zn0.025Te substrates by molecular-beam epitaxy. The structural properties of the superlattices, i.e., the morphology of the layers and the state of strain relaxation, were examined by transmission electron microscopy and x-ray diffractometry. High-resolution transmission electron microscopy (HRTEM) reveals the structural quality of the superlattices on an atomic scale. The width of the chemical transition between the CdTe and CdMgTe layers was determined by HRTEM using chemically sensitive imaging conditions. Two different mechanisms of misfit dislocation generation could be observed in situ in the electron microscope studying a cross-section specimen of a superlattice which was originally fully strained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356643
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  • 5
    Electronic Resource
    Electronic Resource
    Structural transformations and strain relaxation mechanisms of In0.6Ga0.4As islands grown by molecular beam epitaxy on GaAs(001) substrates (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3824-3832 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The shape transformations and the mechanism of misfit strain relaxation of In0.6Ga0.4As islands grown at different temperatures on GaAs(001) substrates have been investigated. Layers with a constant nominal thickness of 12 monolayers were deposited by molecular beam epitaxy on nominal singular and on vicinal substrates. The specimens were characterized by scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. It is shown that an increase of the growth temperature yields a shape transition from rounded islands to elongated cigar-like structures. The lattice-parameter mismatch in the circular islands is relaxed by misfit dislocations at lower growth temperatures. Indium desorption effectively reduces the mismatch at higher growth temperatures and therefore yields the nucleation of coherent islands. In spite of this structural transformation an Arrhenius-like behaviour of the island densities is observed with an activation energy which depends on the substrate tilt. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359897
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  • 6
    Electronic Resource
    Electronic Resource
    Structural properties of ion-beam-synthesized β-FeSi2 in Si(111) (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3788-3794 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A continuous buried β-FeSi2 layer was obtained by implantation of 200 keV Fe+ ions into Si(111) wafers at elevated temperature. During the subsequent rapid thermal annealing at 1150 °C for 10-s, a continuous buried layer of the metallic α-FeSi2 phase is formed. During the second annealing step at 800 °C, the α phase is completely transformed into the semiconducting β phase. The epitaxial relationship between the β-FeSi2 and the silicon substrate was investigated by transmission electron microscopy. It was found that the β-FeSi2(010) plane grows parallel to the Si(111) substrate. Two different azimuthal orientations were observed. For the first azimuthal orientation, the β-FeSi2[001] direction is oriented almost parallel to one of the three Si〈110〉 directions lying in the interface. In the second azimuthal orientation, the β-FeSi2[100] direction lies parallel to one of the Si〈110〉 directions in the interface. The lattice parameter mismatch and the growth mechanism must be considered to be the main reasons for the epitaxial relationship of the Si(111)/β-FeSi2/Si(111) heterostructures studied in this investigation. The orientation of the β-phase is likely to be predetermined by the orientation of the α-phase which is formed during the first annealing step. Different orientation relationships were observed for β-FeSi2 prepared by solid phase epitaxy and ion beam synthesis without high-temperature annealing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350891
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  • 7
    Electronic Resource
    Electronic Resource
    Analysis of composition fluctuations on an atomic scale in Al0.25Ga0.75N by high-resolution transmission electron microscopy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 930-932 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Composition fluctuations in the Al0.25Ga0.75N layer of an AlGaN/GaN transistor structure grown by plasma induced molecular beam epitaxy on Al2O3(0001) at a growth temperature of 870 °C were studied by digital analysis of lattice images (DALI) of high-resolution transmission electron microscopy (HRTEM) cross-section images. DALI exploits the linear dependence of the lattice parameters on the Al content by applying Vegard's law. Detecting the distances between intensity maxima positions in the micrograph which can be considered as a fingerprint of the local lattice parameters quantitatively derives composition profiles on an atomic scale. In the HRTEM cross-section image different areas were observed in the Al0.25Ga0.75N layer with either homogeneous or "striped" contrast. In the striped areas the analyses indicate a strong periodic decomposition with a period of 1 nm consisting of 1 ML Al0.8Ga0.2N and about 3 ML Al0.07Ga0.93N. The regions with homogeneous contrast do not exhibit significant composition fluctuations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122041
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of metalorganic chemical vapor deposition growth conditions on In-rich nanoislands formation in InGaN/GaN structures (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 2099-2101 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4–5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1462868
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  • 9
    Electronic Resource
    Electronic Resource
    Investigation of In segregation in InAs/AlAs quantum-well structures (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4426-4428 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter, we report the investigation of In segregation in InAs/AlAs heterostructures. InAs layers with different thicknesses were grown by molecular beam epitaxy on GaAs (001) substrates. The layers were investigated by transmission electron microscopy. Profiles of the chemical composition of the InAs layers in the [001] direction were deduced from high-resolution lattice fringe images using the composition evaluation by lattice fringe analysis method. The segregation efficiency was derived by fitting the measured In concentration profiles with the segregation model of Muraki et al. [K. Muraki et al., Appl. Phys. Lett. 61, 557 (1992)]. We obtain efficiency of R=0.77±0.03 for the segregation of In in AlAs/InAs at a temperature of 530 °C. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1427148
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  • 10
    Electronic Resource
    Electronic Resource
    InGaN composition and growth rate during the early stages of metalorganic chemical vapor deposition (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2552-2554 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were applied to study the metalorganic chemical vapor deposition of InGaN and the correlation between the structural properties and luminescence of GaN/InxGa1−xN-quantum well structures. A series of samples was grown varying only the growth duration for the InGaN under otherwise unaltered growth conditions. Composition analyses were carried out by measuring local lattice parameters from TEM images, which are directly related to the local In concentration. A rising average In concentration from 6.5% to 15.4% and a decreasing growth rate are observed with increasing growth duration. All samples show an inhomogeneous In distribution containing In-rich agglomerates with a size of only a few nanometers and less pronounced composition fluctuations on a scale of some 10 nm. The redshift of the PL peak energy with increasing quantum well thickness indicates that the luminescence is predominantly determined by the piezoelectric field. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1409949
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