Atomic Layer Deposition: An Overview

Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA.
Chemical Reviews (Impact Factor: 45.66). 11/2009; 110(1):111-31. DOI: 10.1021/cr900056b
Source: PubMed
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    DESCRIPTION: We report on a new fabrication method of producing Bi/Al-codoped silica optical fibers by atomic layer deposition (ALD) in combination with the conventional modified chemical vapor deposition (MCVD) technique. Bi2O3 and Al2O3 are successfully induced into silica optical fiber core layer by ALD technique. Bi2O3 stoichiometry is confirmed by X-ray photoelectron spectroscopy (XPS). The valence state of Bi element is +3. In fiber preform core region, Bi and Al ions have been slightly doped approximately 150-180 and 350-750 ppm, respectively. Refractive index difference of the Bi/Al-codoped fiber is approximately 0.58 %. There are obvious Bi-type ions absorption peaks at 520, 700 and 800 nm. The fluorescence peaks are 1130 and 1145 nm with 489 and 705 nm excitations,respectively. Their fluorescence lifetimes are 701 and 721 μs, respectively. And then there are obvious fluorescence bands in 600-850 and 900-1650 nm with 532 nm pump exciting. There is a maximum fluorescence intensity peak at 1120 nm, and its full wave at half maximum is approximately 180 nm. These may mainly result from the interaction between Bi and Al ions. The Bi/Al-codoped silica optical fibers would be used in high power or broadly tunable laser sources, and optical fiber amplifier in the optical communication fields.
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    ABSTRACT: Keywords: A3. Atomic layer deposition B1. Aluminum nitride Optical band gap Oxygen impurity Refractive index a b s t r a c t A plasma enhanced atomic layer deposition (PEALD) process has been used to deposit crystalline AlN thin films at 250 1C using nitrogen 5% hydrogen plasma and trimethylaluminum precursors. Films grown on single crystal silicon and sapphire substrates are crystalline with strong (100) preferred orientation. Mass density measured by x-ray reflectivity (XRR) was 2.94 g cm À 3 , compared to 3.25 g cm À 3 for the bulk materials. Photoelectron and infrared studies were used to investigate the elemental analysis and the exact bonding environment of the constituents. The optical band gap, measured using spectroscopic ellipsometry, is 6.04 eV, and the refractive index, measured at 632 nm wavelength, is 1.96. The optical properties were thickness-dependent below 30 nm for refractive index and below 15 nm for band gap. &
    Journal of Crystal Growth 05/2015; 421:45-52. DOI:10.1016/j.jcrysgro.2015.04.009 · 1.69 Impact Factor
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    ABSTRACT: A close-proximity atmospheric pressure chemical vapor deposition (AP-CVD) reactor is developed for synthesizing high quality multicomponent metal oxides for electronics. This combines the advantages of a mechanically controllable substrate-manifold spacing and vertical gas flows. As a result, our AP-CVD reactor can rapidly grow uniform crystalline films on a variety of substrate types at low temperatures without requiring plasma enhancements or low pressures. To demonstrate this, we take the zinc magnesium oxide (Zn1-xMgxO) system as an example. By introducing the precursor gases vertically and uniformly to the substrate across the gas manifold, we show that films can be produced with only 3% variation in thickness over a 375 mm^2 deposition area. These thicknesses are significantly more uniform than for films from previous AP-CVD reactors. Our films are also compact, pinhole-free and have a thickness that is linearly controllable by the number of oscillations of the substrate beneath the gas manifold. Using photoluminescence and X-ray diffraction measurements, we show that for Mg contents below 46 at.%, single phase Zn1-xMgxO was produced. To further optimize the growth conditions, we developed a model relating the composition of a ternary oxide with the bubbling rates through the metal precursors. We fitted this model to the X-ray photoelectron spectroscopy measured compositions with an error of Δx = 0.0005. This model showed that the incorporation of Mg into ZnO can be maximized by using the maximum bubbling rate through the Mg precursor for each bubbling rate ratio. When applied to poly(3-hexylthiophene-2,5-diyl) hybrid solar cells, our films yielded an open-circuit voltage increase of over 100% by controlling the Mg content. Such films were deposited in short times (under 2 minutes over 4 cm^2).
    ACS Applied Materials & Interfaces 05/2015; In Press. DOI:10.1021/am5073589 · 5.90 Impact Factor

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