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Freestanding Ge nanocrystals that are stable under ambient conditions have been synthesized in a two-step process. First, nanocrystals with a mean diameter of 5 nm are grown in amorphous SiO2 by ion implantation followed by thermal annealing. The oxide matrix is then removed by selective etching in diluted HF to obtain freestanding nanocrystals on a Si wafer. After etching, nanocrystals are retained on the surface and the size distribution is not significantly altered. Freestanding nanocrystals are stable under ambient atmospheric conditions, suggesting formation of a self-limiting native oxide layer. For freestanding as opposed to embedded Ge nanocrystals, an additional amorphouslike contribution to the Raman spectrum is observed and is assigned to surface reconstruction-induced disordering of near-surface atoms. [ABSTRACT FROM AUTHOR]

GaN template layer strain effects on the growth of InGaN/GaN light emitting diodes devices were investigated. Seven-period InGaN/GaN multiple quantum well structures (MQW) were deposited on 5 and 15 μm GaN template layers. It was found that the electroluminescence emission of the 15 μm device was redshifted by approximately 132 meV. Triple-axis x-ray diffraction and cross-sectional transmission electron microscopy show that the 15 μm template layer device was virtually unstrained while the 5 μm layer experienced tensile strain. Dynamic secondary ion mass spectrometry depth profiles show that the 15 μm template layer device had an average indium concentration of 11% higher than that of the 5 μm template layer device even though the MQW structures were deposited during the same growth run. It was also found that the 15 μm layer device had a higher average growth rate than the 5 μm template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers. [ABSTRACT FROM AUTHOR]

A metallization technique has been developed for obtaining low resistance Ohmic contact to n-GaN. The metallization technique involves the deposition of a metal layer combination Ta/Ti/Ni/Au on an n-GaN epilayer. It is observed that annealing at 750 °C for 45 s leads to low contact resistivity. Corresponding to a doping level of 5×10[sup 17] cm[sup -3], the contact resistivity of the contact ρ[sub S]=5.0×10[sup -6] Ω cm[sup 2]. The physical mechanisms underlying the realization of low contact resistivity is investigated using current–voltage characteristics, x-ray diffraction, Auger electron spectroscopy, transmission electron microscopy, and energy dispersive x-ray spectrometry. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The initial growth mechanism of epitaxial BaTiO[sub 3] films is studied by combined application of atomic force microscopy, cross sectional high-resolution transmission electron microscopy, and x-ray diffraction. Epitaxial BaTiO[sub 3] thin films were grown by pulsed laser deposition on vicinal Nb-doped SrTiO[sub 3] (SrTiO[sub 3]:Nb) (001) substrates with well-defined terraces. X-ray diffraction and cross sectional high-resolution transmission electron microscopy investigations revealed well-defined epitaxial films and a sharp interface between BaTiO[sub 3] films and SrTiO[sub 3]:Nb substrates. The layer-then-island (Stranski-Krastanov mode) growth mechanism observed by analyzing the morphology of a sequence of films with increasing amount of deposited material has been confirmed by microstructure investigations. [ABSTRACT FROM AUTHOR]

Temperature-gradient metalorganic chemical vapor deposition (MOCVD) was used to deposit InxGa1-xN/GaN multiple quantum well (MQW) structures with a concentration gradient of indium across the wafer. These MQW structures were deposited on low defect density (2 x 108 cm-2) GaN template layers for investigation of microstructural properties and V-defect (pinhole) formation. Room temperature (RT) photoluminescence (PL) and photomodulated transmission (PT)were used for optical characterization, which show a systematic decrease in emission energy for a decrease in growth temperature. Triple-axis x-ray diffraction (XRD), scanning electron microscopy, and cross-sectional transmission electron microscopy were used to obtain microstructural properties of different regions across the wafer. Results show that there is a decrease in crystal quality and an increase in V-defect formation with increasing indium concentration. A direct correlation was found between V-defect density and growth temperature due to increased strain and indium segregation for increasing indium concentration. [ABSTRACT FROM AUTHOR]

(Ba 0.7 Sr 0.3 )TiO 3 thin films were prepared by chemical solution deposition on Si/SiO 2 /Ti/Pt substrates and subsequently crystallized by isothermal annealing at 550, 600, 700 and 800°C, respectively. TEM analysis of the film annealed at 550°C showed the presence of residual amorphous phase. Further rise of the annealing temperature led to complete crystallization of films which had polycrystalline structure. Two types of BST grains (type I and type II) have been observed. It was found that the relative content of the type I grains drastically decreased as the temperature had been raised up, and the film crystallized at 800°C consisted of type II grains only. The effect of different types of BST grains on dielectric properties is discussed. [ABSTRACT FROM AUTHOR]

We report the experimental demonstration of deep-submicrometer inversion-mode In0.75Ga0.25As MOSFETs with ALD high-k Al2O3 as gate dielectric. In this letter, n-channel MOSFETs with 100-200-nm-long gates have been fabricated. At a supply voltage of 0.8 V, the fabricated devices with 200-130-nm-long gates exhibit drain currents of 232-440 μA/μm and transconductances of 538-705 μ/μm. The 100-nm device has a drain current of 801 μA/μm and a transconductance of 940 μS/μm. However, the device cannot be pinched off due to severe short-channel effect. Important scaling metrics, such as on/off current ratio, subthreshold swing, and drain-induced barrier lowering, are presented, and their relations to the short-channel effect are discussed. [ABSTRACT FROM AUTHOR]

Ion-beam-synthesized 74Ge nanocrystals embedded in an amorphous silica matrix exhibit large compressive stresses in the as-grown state. The compressive stress is determined quantitatively by evaluating the Raman line shift referenced to the line position of free-standing nanocrystals. Postgrowth thermal treatments lead to stress reduction. The stress relief process is shown to be governed by the diffusive flux of matrix atoms away from the local nanocrystal growth region. A theoretical model that quantitatively describes this process is presented. [ABSTRACT FROM AUTHOR]