Undoped 69GaAs/71GaAs isotope superlattice structures grown by MBE on n-type GaAs substrates, doped by Si to ~3x1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature...
Undoped 69GaAs/71GaAs isotope superlattice structures grown by MBE on n-type GaAs substrates, doped by Si to ~3x1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960 °C, the SIMS measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and AI-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. SIMS, CV, and TEM characterizations showed that the as-grown superlattice layers were intrinsic which became p-type with hole concentrations up to ~2x1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ~106–107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si outdiffusion from the substrate, which was determined using CV measurements. Outdiffusion of Si decreases the n value in the substrate which causes the release of excess Ga vacancies into the superlattice layers where the supersaturated Ga vacancies enhance Ga self-diffusion.
S. Strite, J. Ruan, Z. Li, N. Manning, A. Salvador, H. Chen, David J. Smith, W. J. Choyke, H. Morkoç; Erratum: An investigation of the properties of cubic GaN g
S. Strite, J. Ruan, Z. Li, N. Manning, A. Salvador, H. Chen, David J. Smith, W. J. Choyke, H. Morkoç; Erratum: An investigation of the properties of cubic GaN g
We have grown by molecular beam epitaxy (MBE) CuCl thin films at various thicknesses and substrate temperatures on CaF 2 (111) substrates. Atomic force microscope (AFM) topographs reveal that islanding is the dominant...
We have grown by molecular beam epitaxy (MBE) CuCl thin films at various thicknesses and substrate temperatures on CaF 2 (111) substrates. Atomic force microscope (AFM) topographs reveal that islanding is the dominant growth mechanism. Quantitative analysis of the AFM data enabled us to determine the amount of the substrate remaining exposed after the deposition as well as the total amount of CuCl deposited. We calculated the reciprocal-space height correlation function, 〈| h ( q , t )| 2 〉, for each of our films and compared them to the predictions of the shadoqing growth theory, which enabled us to extract the important kinetic parameter of surface diffusion length for the growth condition of each of the four films.
We present the first comprehensive investigation of the bulk properties, both optical and structural, of cubic GaN as grown by plasma-assisted molecular-beam epitaxy on vicinal (100) GaAs substrates. X-ray measurement...
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The nanostructure evolution of PZT, PT and T thin films has been studied by high-resolution electron microscopy (HREM) supported by other techniques such as thermal analysis, thermal mass spectrometric analysis and X-...
The nanostructure evolution of PZT, PT and T thin films has been studied by high-resolution electron microscopy (HREM) supported by other techniques such as thermal analysis, thermal mass spectrometric analysis and X-ray diffraction analysis. The evolution follows a common progression from amorphous film, to the development of condensed regions that develop crystalline order, to the final polycrystalline oxide thin film. If the precursor gel contains lead, the film develops fluctuating surface “blisters” that evolve to an oxide final product as well. Minor structural and compositional differences exist across the final oxide thin film.
CdS and CdTe auantum dots (QDs) precipitated from borosilicate glass matrices, exhibiting auantum confinement effects, have been characterized by optical spectroscopy and high-spatial-resolution electron microscopy. T...
CdS and CdTe auantum dots (QDs) precipitated from borosilicate glass matrices, exhibiting auantum confinement effects, have been characterized by optical spectroscopy and high-spatial-resolution electron microscopy. The particles appear to have formed initially by homogeneous nucleation and were randomly distributed, but the morphology of the particles and therefore growth processes differ. The CdTe particles were spherical single crystals, often with smali facets on {111} planes, or at most bicrystals. The measured average diameter of these particles was about 14 nm. They had a zinc-blende cubic structure with lattice constant corresponding to bulk CdTe crystals. For CdS the particles were relatively large polycrystals, composed of smaller single crystals, whose size was about 3–3 nm. The structure of these nanocrystals was wurzite-type hexagonal, with a lattice corresponding to CdS. Particle-size effects on absorption peak shifts were observed for both CdTe and CdS samples. Microscopically observed QD sizes were compared with predictions of theoretical models based on optical absorption features of quantum confined structures.
The microstructural development and grain growth of YBa2Cu3O7y ceramics at 925, 950, and 975 C were studied. Densification occurred quite rapidly at temperatures below 925 C. The grain growth of YBa2Cu3O7y followed a ...
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The microstructural development and grain growth of YBa2Cu3O7y ceramics at 925, 950, and 975 C were studied. Densification occurred quite rapidly at temperatures below 925 C. The grain growth of YBa2Cu3O7y followed a D5 D50 = Kt relation when sintered at 925 and 950 C. At 975 C, the kinetics changed to cubic (D3) behavior, which can be attributed to the formation of a liquid phase at grain boundaries. A trend of decreasing Jc with increasing sintering temperature was observed. Other properties including Tc and the width of the transition were virtually unaffected by the change in microstructure. Without prolonged annealing, a relatively homogeneous oxygen stoichiometry of 6.8 was obtained for fairly dense samples (>93% of theoretical). These results suggest that the oxygenation rate of YBa2Cu3O7y was quite rapid between the tetragonal phase and the orthorhombic composition of YBa2Cu3O6.8.
We have employed a first‐principles computer program to simulate actual potential profiles and potential profiles obtained experimentally from the Kelvin probe technique. Our results show that the Kelvin probe techni...
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We have employed a first‐principles computer program to simulate actual potential profiles and potential profiles obtained experimentally from the Kelvin probe technique. Our results show that the Kelvin probe technique can be used as an in situ method for qualitatively characterizing amorphous films and structures during deposition. However, without additional information about the density and energy distribution of localized states in the bulk and at the free surface, we find that it is difficult to obtain, from the Kelvin probe measurement alone, an accurate quantitative measure of the actual spatial dependence of band bending in films and device structures. In addition, this computer analysis shows that interpretation of the profiles obtained from the Kelvin probe contact potential method can lead to misleading conclusions about the density of states in these amorphous materials. We also show that the barrier height of Schottky contacts or the built‐in potential of junctions of differently doped layers can be obtained directly from Kelvin probe contact potential measurements only for films whose free‐surface band bending is known from other experimental data. We see that this surface band bending can be significant even for small free‐surface‐state densities and is more pronounced in higher‐quality films.
Interfaces between aluminum and silicon in samples prepared by solidification of an Al-Si eutectic liquid have been studied by high-resolution electron microscopy. The Al and Si grains have a common [110] axis with a ...
Interfaces between aluminum and silicon in samples prepared by solidification of an Al-Si eutectic liquid have been studied by high-resolution electron microscopy. The Al and Si grains have a common [110] axis with a misorientation between grains of 70.5°, thus aligning the (lll)Si plane with the (111)Alplane. In general, theinterfaces have a complex structurewith numerous interfacial dislocations and considerable facetting. The core structurescan be characterized in terms of structural unit models. The nature of the facetting has also been investigated, in particular one facet which lies approximately along the (111)Al, and (l15)Si planes and another which lies approximately along the (110)Al and (l14)Si planes.
High-resolution electron microscopic examination of alkoxide thin-film gels has been employed to study the drying and aging of thin-film Pb(Zr0.45Ti0.55)O2(OR)2 as it evolves from the gel to the ferroelectric perovski...
High-resolution electron microscopic examination of alkoxide thin-film gels has been employed to study the drying and aging of thin-film Pb(Zr0.45Ti0.55)O2(OR)2 as it evolves from the gel to the ferroelectric perovskite product. The initially amorphous film is observed to aggregate to form ordered islands with inter-metal distances close to that of the final structure embedded in a highly disordered matrix. When these aggregates are at the surface they grow and decompose more rapidly to the perovskite product. The progress to a polycrystalline final state is followed and recorded in real time and in time-lapse at high resolution.
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