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Synthesis and modeling of uniform complex metal oxides by close-proximity atmospheric pressure chemical vapor deposition Robert L. Z. Hoye, David Muñoz-Rojas, Kevin P. Musselman, Yana Vaynzof, and Judith L. MacManus-Driscoll ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/am5073589 • Publication Date (Web): 05 May 2015 Downloaded from http://pubs.acs.org on May 10, 2015
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ACS Applied Materials & Interfaces
Synthesis and modeling of uniform complex metal oxides by close-proximity atmospheric pressure chemical vapor deposition Robert L. Z. Hoye,† David Muñoz-Rojas, †,‡ Kevin P. Musselman,‖,† Yana Vaynzof, ‖ , Ϯ and Judith L. MacManus-Driscoll*,† †Department
of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage
Road, Cambridge CB3 0FS, UK ‡
LMGP, University Grenoble-Alpes, CNRS, F-3800 Grenoble, France
‖Department
of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE,
UK
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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 mm2 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 cm2).
KEYWORDS: atmospheric pressure chemical vapor deposition, zinc magnesium oxide, multicomponent metal oxides, bandgap tuning, solar cells, spatial atmospheric atomic layer deposition
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ACS Applied Materials & Interfaces
INTRODUCTION
Metal oxides are widely used for optoelectronic applications,1–3 due to their stability, composition of non-toxic and earth-abundant elements, and intrinsic semiconductivity.4 It is crucial that these metal oxides can be produced scalably, so that the devices can be manufactured on an industrial level.4 Chemical vapor deposition (CVD) is an appealing metal oxide deposition technique, due to the high growth rates possible.5,6 But CVD is limited by requiring high deposition temperatures (often >350 °C),7 with plasmas or low pressure processing needed to reduce deposition temperatures.6–8 Atomic layer deposition (ALD) is another appealing metal oxide deposition technique. ALD is a subset of CVD,6 but only involves surface half-reactions,9 rather than the gas-phase and surface reactions used in CVD.6 This allows uniform films with nanometer-level thickness control to be deposited at lower temperatures (~120 °C for ZnO) conformally onto both flat substrates and high aspect-ratio substrates.9–11 Growing films below 155 °C is important for compatibility with flexible polymer substrates, in addition to a lower energy consumption.12,13 ALD is, however, limited by lower growth rates because it separates the exposure of the metal precursors and oxidant to the substrate in time by purging a closedreaction chamber between each pulse.12,13 Atmospheric pressure spatial atomic layer deposition (AP-SALD) overcomes these limitations by spatially separating the precursors.13,14 AP-SALD is commonly implemented with the close-proximity design,13,15–17 in which the substrate is oscillated
