Showing papers on "Atomic layer deposition published in 2012"

Water Oxidation at Hematite Photoelectrodes: The Role of Surface States

Abstract: Hematite (α-Fe2O3) constitutes one of the most promising semiconductor materials for the conversion of sunlight into chemical fuels by water splitting. Its inherent drawbacks related to the long penetration depth of light and poor charge carrier conductivity are being progressively overcome by employing nanostructuring strategies and improved catalysts. However, the physical–chemical mechanisms responsible for the photoelectrochemical performance of this material (J(V) response) are still poorly understood. In the present study we prepared thin film hematite electrodes by atomic layer deposition to study the photoelectrochemical properties of this material under water-splitting conditions. We employed impedance spectroscopy to determine the main steps involved in photocurrent production at different conditions of voltage, light intensity, and electrolyte pH. A general physical model is proposed, which includes the existence of a surface state at the semiconductor/liquid interface where holes accumulate. T...

Microwave Absorption Properties of Carbon Nanocoils Coated with Highly Controlled Magnetic Materials by Atomic Layer Deposition

Abstract: In this work, atomic layer deposition is applied to coat carbon nanocoils with magnetic Fe(3)O(4) or Ni. The coatings have a uniform and highly controlled thickness. The coated nanocoils with coaxial multilayer nanostructures exhibit remarkably improved microwave absorption properties compared to the pristine carbon nanocoils. The enhanced absorption ability arises from the efficient complementarity between complex permittivity and permeability, chiral morphology, and multilayer structure of the products. This method can be extended to exploit other composite materials benefiting from its convenient control of the impedance matching and combination of dielectric-magnetic multiple loss mechanisms for microwave absorption applications.

Status and prospects of Al2O3-based surface passivation schemes for silicon solar cells

Abstract: The reduction in electronic recombination losses by the passivation of silicon surfaces is a critical enabler for high-efficiency solar cells. In 2006, aluminum oxide (Al2O3) nanolayers synthesized by atomic layer deposition (ALD) emerged as a novel solution for the passivation of p- and n-type crystalline Si (c-Si) surfaces. Today, high efficiencies have been realized by the implementation of ultrathin Al2O3 films in laboratory-type and industrial solar cells. This article reviews and summarizes recent work concerning Al2O3 thin films in the context of Si photovoltaics. Topics range from fundamental aspects related to material, interface, and passivation properties to synthesis methods and the implementation of the films in solar cells. Al2O3 uniquely features a combination of field-effect passivation by negative fixed charges, a low interface defect density, an adequate stability during processing, and the ability to use ultrathin films down to a few nanometers in thickness. Although various methods can be used to synthesize Al2O3, this review focuses on ALD—a new technology in the field of c-Si photovoltaics. The authors discuss how the unique features of ALD can be exploited for interface engineering and tailoring the properties of nanolayer surface passivation schemes while also addressing its compatibility with high-throughput manufacturing. The recent progress achieved in the field of surface passivation allows for higher efficiencies of industrial solar cells, which is critical for realizing lower-cost solar electricity in the near future.

Coking- and Sintering-Resistant Palladium Catalysts Achieved Through Atomic Layer Deposition

Abstract: We showed that alumina (Al(2)O(3)) overcoating of supported metal nanoparticles (NPs) effectively reduced deactivation by coking and sintering in high-temperature applications of heterogeneous catalysts We overcoated palladium NPs with 45 layers of alumina through an atomic layer deposition (ALD) process that alternated exposures of the catalysts to trimethylaluminum and water at 200°C When these catalysts were used for 1 hour in oxidative dehydrogenation of ethane to ethylene at 650°C, they were found by thermogravimetric analysis to contain less than 6% of the coke formed on the uncoated catalysts Scanning transmission electron microscopy showed no visible morphology changes after reaction at 675°C for 28 hours The yield of ethylene was improved on all ALD Al(2)O(3) overcoated Pd catalysts

Photoelectrochemical and Impedance Spectroscopic Investigation of Water Oxidation with "Co−Pi"-Coated Hematite Electrodes

Abstract: Uniform thin films of hematite (α-Fe(2)O(3)) deposited by atomic layer deposition (ALD) coated with varying amounts of the cobalt phosphate catalyst, "Co-Pi," were investigated with steady-state and transient photoelectrochemical measurements and impedance spectroscopy. Systematic studies as a function of Co-Pi thickness were performed in order to clarify the mechanism by which Co-Pi enhances the water-splitting performance of hematite electrodes. It was found that under illumination, the Co-Pi catalyst can efficiently collect and store photogenerated holes from the hematite electrode. This charge separation reduces surface state recombination which results in increased water oxidation efficiency. It was also found that thicker Co-Pi films produced increased water oxidation efficiencies which is attributed to a combination of superior charge separation and increased surface area of the porous catalytic film. These combined results provide important new understanding of the enhancement and limitations of the Co-Pi catalyst coupled with semiconductor electrodes for water-splitting applications.

Atomic Layer Deposition of Nanostructured Materials for Energy and Environmental Applications

Abstract: Atomic layer deposition (ALD) is a thin film technology that in the past two decades rapidly developed from a niche technology to an established method. It proved to be a key technology for the surface modification and the fabrication of complex nanostructured materials. In this Progress Report, after a short introduction to ALD and its chemistry, the versatility of the technique for the fabrication of novel functional materials will be discussed. Selected examples, focused on its use for the engineering of nanostructures targeting applications in energy conversion and storage, and on environmental issues, will be discussed. Finally, the challenges that ALD is now facing in terms of materials fabrication and processing will be also tackled.

Atomic layer deposition of vanadium oxide on carbon nanotubes for high-power supercapacitor electrodes

Abstract: Vanadium oxides may offer high pseudocapacitance but limited electrical conductivity and specific surface area. Atomic layer deposition allowed uniform deposition of smooth nanostructured vanadium oxide coatings on the surface of multi-walled carbon nanotube (MWCNT) electrodes, thus offering a novel route for the formation of binder-free flexible composite electrode fabric for supercapacitor applications with large thickness, controlled porosity, greatly improved electrical conductivity and cycle stability. Electrochemical measurements revealed stable performance of the selected MWCNT–vanadium oxide electrodes and remarkable capacitance of up to ∼1550 F g−1 per active mass of the vanadium oxide and up to ∼600 F g−1 per mass of the composite electrode, significantly exceeding specific capacitance of commercially used activated carbons (100–150 F g−1). Electrochemical performance of the oxide layers was found to strongly depend on the coating thickness.

Tin Oxide with Controlled Morphology and Crystallinity by Atomic Layer Deposition onto Graphene Nanosheets for Enhanced Lithium Storage

Abstract: As one of the most promising negative electrode materials in lithium-ion batteries (LIBs), SnO 2 experiences intense investigation due to its high specifi c capacity and energy density, relative to conventional graphite anodes. In this study, for the fi rst time, atomic layer deposition (ALD) is used to deposit SnO 2 , containing both amorphous and crystalline phases, onto graphene nanosheets (GNS) as anodes for LIBs. The resultant SnO 2 -graphene nanocomposites exhibit a sandwich structure, and, when cycled against a lithium counter electrode, demonstrate a promising electrochemical performance. It is demonstrated that the introduction of GNS into the nanocomposites is benefi cial for the anodes by increasing their electrical conductivity and releasing strain energy: thus, the nanocomposite electrode materials maintain a high electrical conductivity and fl exibility. It is found that the amorphous SnO 2 -GNS is more effective than the crystalline SnO 2 -GNS in overcoming electrochemical and mechanical degradation; this observation is consistent with the intrinsically isotropic nature of the amorphous SnO 2 , which can mitigate the large volume changes associated with charge/discharge processes. It is observed that after 150 charge/discharge cycles, 793 mA h g − 1 is achieved. Moreover, a higher coulombic effi ciency is obtained for the amorphous SnO 2 GNS composite anode. This study provides an approach to fabricate novel anode materials and clarifi es the infl uence of SnO 2 phases on the electrochemical performance of LIBs.

Ultrathin films on copper(I) oxide water splitting photocathodes: a study on performance and stability

Abstract: The utilisation of Cu2O photocathodes for photoelectrochemical water splitting requires their stabilisation due to photocorrosion in aqueous electrolytes. Ultrathin films of wide band gap semiconducting oxides deposited by atomic layer deposition (ALD) on top of cuprous oxide can perform the dual function of both facilitating charge extraction (through the creation of a p–n junction) and protecting the absorber material from the aqueous electrolyte, thereby suppressing corrosion in favor of hydrogen generation. The factors that determine the photocurrent performance as well as the stability of these photoelectrodes are examined. Specifically, the influence of ALD deposition temperature, electrolyte pH, electrolyte composition as well as post-deposition annealing treatments was studied. The successful development of protective overlayers must fulfil the dual requirements of favourable band alignments as well as chemical stability. At long time scales, the deactivation of the photocathodes proceeds through etching of the amorphous overlayer, accompanied by the loss of the platinum catalyst particles. Through the deposition of a semi-crystalline TiO2 overlayer, 62% stability over 10 hours of testing has been demonstrated without re-platinization.

$\hbox{MoS}_{2}$ Dual-Gate MOSFET With Atomic-Layer-Deposited $\hbox{Al}_{2}\hbox{O}_{3}$ as Top-Gate Dielectric

Abstract: We demonstrate atomic-layer-deposited (ALD) high-k dielectric integration on 2-D layer-structured molybdenum disulfide (MoS2) crystals and MoS2 dual-gate n-channel MOSFETs with ALD Al2O3 as the gate dielectric. Our C- V study of MOSFET structures shows good interface between 2-D MoS2 crystal and ALD Al2O3. Maximum drain currents using back gates and top gates are measured to be 7.07 and 6.42 mA/mm, respectively, at Vds = 2 V with a channel width of 3 μm, a channel length of 9 μm, and a top-gate length of 3 μm. We achieve the highest field-effect mobility of electrons using back-gate control to be 517 cm2/V·s. The highest current on/off ratio is over 108.

Photoelectrochemical properties of TiO2 nanowire arrays: a study of the dependence on length and atomic layer deposition coating.

Abstract: We report that the length and surface properties of TiO2 nanowires can have a dramatic effect on their photoelectrochemical properties. To study the length dependence, rutile TiO2 nanowires (0.28–1.8 μm) were grown on FTO substrates with different reaction times (50–180 min) using a hydrothermal method. Nanowires show an increase in photocurrent with length, and a maximum photocurrent of 0.73 mA/cm2 was measured (1.5 V vs RHE) for 1.8 μm long nanowires under AM 1.5G simulated sunlight illumination. While the incident photon to current conversion efficiency (IPCE) increases linearly with photon absorptance (1–10–α×length) with near band gap illumination (λ = 410 nm), it decreases severely at shorter wavelengths of light for longer nanowires due to poor electron mobility. Atomic layer deposition (ALD) was used to deposit an epitaxial rutile TiO2 shell on nanowire electrodes which enhanced the photocatalytic activity by 1.5 times (1.5 V vs RHE) with 1.8 μm long nanowires, reaching a current density of 1.1 mA...

Atomic Layer Deposition of Vanadium Oxide on Carbon Nanotubes for High-Power Supercapacitor Electrodes

Abstract: Vanadium oxides may offer high pseudocapacitance but limited electrical conductivity and specific surface area. Atomic layer deposition allowed uniform deposition of smooth nanostructured vanadium oxide coatings on the surface of multi-walled carbon nanotube (MWCNT) electrodes, thus offering a novel route for the formation of binder-free flexible composite electrode fabric for supercapacitor applications with large thickness, controlled porosity, greatly improved electrical conductivity and cycle stability. Electrochemical measurements revealed stable performance of the selected MWCNT–vanadium oxide electrodes and remarkable capacitance of up to ∼1550 F g−1 per active mass of the vanadium oxide and up to ∼600 F g−1 per mass of the composite electrode, significantly exceeding specific capacitance of commercially used activated carbons (100–150 F g−1). Electrochemical performance of the oxide layers was found to strongly depend on the coating thickness.

Growth of p-type hematite by atomic layer deposition and its utilization for improved solar water splitting.

Abstract: Mg-doped hematite (α-Fe2O3) was synthesized by atomic layer deposition (ALD). The resulting material was identified as p-type with a hole concentration of ca. 1.7 × 1015 cm–3. When grown on n-type hematite, the p-type layer was found to create a built-in field that could be used to assist photoelectrochemical water splitting reactions. A nominal 200 mV turn-on voltage shift toward the cathodic direction was measured, which is comparable to what has been measured using water oxidation catalysts. This result suggests that it is possible to achieve desired energetics for solar water splitting directly on metal oxides through advanced material preparations. Similar approaches may be used to mitigate problems caused by energy mismatch between water redox potentials and the band edges of hematite and many other low-cost metal oxides, enabling practical solar water splitting as a means for solar energy storage.

Spatial atomic layer deposition: A route towards further industrialization of atomic layer deposition

Abstract: Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this drawback is spatial ALD, i.e., an ALD mode where the half-reactions are separated spatially instead of through the use of purge steps. This allows for high deposition rate and high throughput ALD without compromising the typical ALD assets. This paper gives a perspective of past and current developments in spatial ALD. The technology is discussed and the main players are identified. Furthermore, this overview highlights current as well as new applications for spatial ALD, with a focus on photovoltaics and flexible electronics. 2012 American Vacuum Society.

Colloidal Atomic Layer Deposition (c-ALD) using Self-Limiting Reactions at Nanocrystal Surface Coupled to Phase Transfer between Polar and Nonpolar Media

Abstract: Atomic layer deposition (ALD) is widely used for gas-phase deposition of high-quality dielectric, semiconducting, or metallic films on various substrates. In this contribution we propose the concept of colloidal ALD (c-ALD) for synthesis of colloidal nanostructures. During the c-ALD process, either nanoparticles or molecular precursors are sequentially transferred between polar and nonpolar phases to prevent accumulation of unreacted precursors and byproducts in the reaction mixture. We show that binding of inorganic ligands (e.g., S2–) to the nanocrystal surface can be used as a half-reaction in c-ALD process. The utility of this approach has been demonstrated by growing CdS layers on colloidal CdSe nanocrystals, nanoplatelets, and CdS nanorods. The CdS/CdSe/CdS nanoplatelets represent a new example of colloidal nanoheterostructures with mixed confinement regimes for electrons and holes. In these materials holes are confined to a thin (∼1.8 nm) two-dimensional CdSe quantum well, while the electron confin...

Active MnOx Electrocatalysts Prepared by Atomic Layer Deposition for Oxygen Evolution and Oxygen Reduction Reactions

Abstract: The ability to deposit conformal catalytic thin films enables opportunities to achieve complex nanostructured designs for catalysis. Atomic layer deposition (ALD) is capable of creating conformal thin films over complex substrates. Here, ALD-MnOx on glassy carbon is investigated as a catalyst for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), two reactions that are of growing interest due to their many applications in alternative energy technologies. The films are characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, ellipsometry, and cyclic voltammetry. The as-deposited films consist of Mn(II)O, which is shown to be a poor catalyst for the ORR, but highly active for the OER. By controllably annealing the samples, Mn2O3 catalysts with good activity for both the ORR and OER are synthesized. Hypotheses are presented to explain the large difference in the activity between the MnO and Mn2O3 catalysts for the ORR, but similar activity for the OER, including the effects of surface oxidation under experimental conditions. These catalysts synthesized though ALD compare favorably to the best MnOx catalysts in the literature, demonstrating a viable way to produce highly active, conformal thin films from earth-abundant materials for the ORR and the OER.

MWCNT/V2O5 core/shell sponge for high areal capacity and power density Li-ion cathodes.

Abstract: A multiwall carbon nanotube (MWCNT) sponge network, coated by ALD V(2)O(5), presents the key characteristics needed to serve as a high-performance cathode in Li-ion batteries, exploiting (1) the highly electron-conductive nature of MWCNT, (2) unprecedented uniformity of ALD thin film coatings, and (3) high surface area and porosity of the MWCNT sponge material for ion transport. The core/shell MWCNT/V(2)O(5) sponge delivers a stable high areal capacity of 816 μAh/cm(2) for 2 Li/V(2)O(5) (voltage range 4.0-2.1 V) at 1C rate (1.1 mA/cm(2)), 450 times that of a planar V(2)O(5) thin film cathode. At much higher current (50×), the areal capacity of 155 μAh/cm(2) provides a high power density of 21.7 mW/cm(2). The compressed sponge nanoarchitecture thus demonstrates exceptional robustness and energy-power characteristics for thin film cathode structures for electrochemical energy storage.

Nanolayer deposition process

Abstract: A hybrid deposition process of CVD and ALD, called NanoLayer Deposition (NLD) is provided. The NLD process is a cyclic sequential deposition process, including introducing a first plurality of precursors to deposit a thin film and introducing a second plurality of precursors to modify the deposited thin film. The deposition using the first set of precursors is not self limiting and is a function of substrate temperature and process time. The second set of precursors modifies the already deposited film characteristics. The second set of precursors can treat the deposited film, including treatments such as modification of film composition and doping or removal of impurities from the deposited film. The second set of precursors can also deposit another layer on the deposited film. The additional layer can react with the existing layer to form a compound layer, or can have minimum reaction to form a nanolaminate film.

Effective Passivation of AlGaN/GaN HEMTs by ALD-Grown AlN Thin Film

Abstract: An effective passivation technique for AlGaN/GaN high-electron-mobility transistors (HEMTs) is presented. This technique features an AlN thin film grown by plasma-enhanced atomic layer deposition (PEALD). With in situ remote plasma pretreatments prior to the AlN deposition, an atomically sharp interface between ALD-AlN and III-nitride has been obtained. Significant current collapse suppression and dynamic ON-resistance reduction are demonstrated in the ALD-AlN-passivated AlGaN/GaN HEMTs under high-drain-bias switching conditions.

Atomic Layer Deposition of TiO2 on Graphene for Supercapacitors

Abstract: A nano-scaled coating of titanium oxide (TiO2) on graphene (G) has been achieved via a novel atomic layer deposition (ALD) method. As a potential supercapacitor material, the TiO2-G composites exhibited a capacity of 75 F/g and 84 F/g at a scan rate of 10 mV/s for composites grown using 50 and 100 ALD cycles, respectively. The nearly identical Nyquist plots of the TiO2-G composites compared with those of pure graphene demonstrated that the composites possess excellent conductivity for charge transfer and open structures for ion diffusion. In addition, even with 3-4 times additional mass loading (maximum 3.22 mg/cm2), the composites exhibit no obvious degradation with respect to the electrochemical performance. This ALD approach presents a promising route to synthesize advanced graphene-based nanocomposites for supercapacitor applications. © 2012 The Electrochemical Society. [DOI: 10.1149/2.025204jes] All rights reserved.

Conformal doping via plasma activated atomic layer deposition and conformal film deposition

Abstract: Disclosed herein are methods of doping a patterned substrate in a reaction chamber. The methods may include forming a first conformal film layer which has a dopant source including a dopant, and driving some of the dopant into the substrate to form a conformal doping profile. In some embodiments, forming the first film layer may include introducing a dopant precursor into the reaction chamber, adsorbing the dopant precursor under conditions whereby it forms an adsorption-limited layer, and reacting the adsorbed dopant precursor to form the dopant source. Also disclosed herein are apparatuses for doping a substrate which may include a reaction chamber, a gas inlet, and a controller having machine readable code including instructions for operating the gas inlet to introduce dopant precursor into the reaction chamber so that it is adsorbed, and instructions for reacting the adsorbed dopant precursor to form a film layer containing a dopant source.

Improved Functionality of Lithium‐Ion Batteries Enabled by Atomic Layer Deposition on the Porous Microstructure of Polymer Separators and Coating Electrodes

Abstract: Atomic layer deposition (ALD) of Al2O3 is applied on a polypropylene separator for lithium-ion batteries. A thin Al2O3 layer (<10 nm) is coated on every surface of the porous polymer microframework without significantly increasing the total separator thickness. The thin Al2O3 ALD coating results in significantly suppressed thermal shrinkage, which may lead to improved safety of the batteries. More importantly, the wettability of Al2O3 ALD-coated separators in an extremely polar electrolyte based on pure propylene carbonate (PC) solvent is demonstrated, without any decrease in electrochemical performances such as capacity, rate capability, and cycle life. Finally, a LiCoO2/natural graphite full cell is demonstrated under extremely severe conditions (pure PC-based electrolyte and high (4.5 V) upper cut-off potential), which is enabled by the Al2O3 ALD coating on all three components (cathode, anode, and separator).

Atomic layer deposition for photovoltaics: applications and prospects for solar cell manufacturing

Abstract: Atomic layer deposition (ALD) is a vapour-phase deposition technique capable of depositing high quality, uniform and conformal thin films at relatively low temperatures. These outstanding properties can be employed to face processing challenges for various types of next-generation solar cells; hence, ALD for photovoltaics (PV) has attracted great interest in academic and industrial research in recent years. In this review, the recent progress of ALD layers applied to various solar cell concepts and their future prospects are discussed. Crystalline silicon (c-Si), copper indium gallium selenide (CIGS) and dye-sensitized solar cells (DSSCs) benefit from the application of ALD surface passivation layers, buffer layers and barrier layers, respectively. ALD films are also excellent moisture permeation barriers that have been successfully used to encapsulate flexible CIGS and organic photovoltaic (OPV) cells. Furthermore, some emerging applications of the ALD method in solar cell research are reviewed. The potential of ALD for solar cells manufacturing is discussed, and the current status of high-throughput ALD equipment development is presented. ALD is on the verge of being introduced in the PV industry and it is expected that it will be part of the standard solar cell manufacturing equipment in the near future.

Subnanometer Ga2O3 tunnelling layer by atomic layer deposition to achieve 1.1 V open-circuit potential in dye-sensitized solar cells.

Abstract: Herein, we present the first use of a gallium oxide tunnelling layer to significantly reduce electron recombination in dye-sensitized solar cells (DSC). The subnanometer coating is achieved using atomic layer deposition (ALD) and leading to a new DSC record open-circuit potential of 1.1 V with state-of-the-art organic D-π-A sensitizer and cobalt redox mediator. After ALD of only a few angstroms of Ga(2)O(3), the electron back reaction is reduced by more than an order of magnitude, while charge collection efficiency and fill factor are increased by 30% and 15%, respectively. The photogenerated exciton separation processes of electron injection into the TiO(2) conduction band and the hole injection into the electrolyte are characterized in detail.

Hollow core–shell nanostructure supercapacitor electrodes: gap matters

Abstract: Hollow core–shell nanorods with a nanogap are designed and constructed with the assistance of atomic layer deposition (ALD) for energy storage applications. As a demonstration, CoO nanorods and NiO nanowalls are enclosed by a TiO2 nanotube shell, forming the “wire in tube” and “wall in box” structures, respectively. A thin sacrificial layer of Al2O3 is deposited by ALD and removed eventually, forming a nanogap between the CoO core (or the NiO nanowall) and the TiO2 shell. When they are tested as supercapacitor electrodes, an evident difference between the solid core–shell nanostructure and hollow ones can be found; for example, the hollow structure shows ∼2 to 4 times the capacitance compared to the solid wires. The electrochemical properties are also superior compared to the bare nanorods without the nanotube shell. The enhancement is ascribed to the conformal hollow design which provides enlarged specific surface areas and a shorter ion transport path. It is prospected that such a positive nanogap effect may also exist in other electrochemical cell electrodes such as lithium ion batteries and fuel cells.

Nanoscale Interface Modification of LiCoO2 by Al2O3 Atomic Layer Deposition for Solid-State Li Batteries

Abstract: Cycle stability of solid-state lithium batteries (SSLBs) using a LiCoO2 cathode is improved by atomic layer deposition (ALD) on active material powder with Al2O3. SSLBs with LiCoO2/Li3.15Ge0.15P0.85S4/77.5Li2S-22.5P2S5/Li structure were constructed and tested by charge-discharge cycling at a current density of 45 μA cm−2 with a voltage window of 3.3 ~ 4.3 V (vs. Li/Li+). Capacity degradation during cycling is suppressed dramatically by employing Al2O3 ALD-coated LiCoO2 in the composite cathode. Whereas only 70% of capacity retention is achieved for uncoated LiCoO2 after 25 cycles, 90% of capacity retention is observed for LiCoO2 with ALD Al2O3 layers. Electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) studies show that the presence of ALD Al2O3 layers on the surface of LiCoO2 reduces interfacial resistance development between LiCoO2 and solid state electrolyte (SSE) during cycling.

Creation and Control of Two-Dimensional Electron Gas Using Al-Based Amorphous Oxides/SrTiO3 Heterostructures Grown by Atomic Layer Deposition

Abstract: The formation of a two-dimensional electron gas (2-DEG) using SrTiO3 (STO)-based heterostructures provides promising opportunities in oxide electronics. We realized the formation of 2-DEG using several amorphous layers grown by the atomic layer deposition (ALD) technique at 300 °C which is a process compatible with mass production and thereby can provide the realization of potential applications. We found that the amorphous LaAlO3 (LAO) layer grown by the ALD process can generate 2-DEG (∼1 × 1013/cm2) with an electron mobility of 4–5 cm2/V·s. A much higher electron mobility was observed at lower temperatures. More remarkably, amorphous YAlO3 (YAO) and Al2O3 layers, which are not polar-perovskite-structured oxides, can create 2-DEG as well. 2-DEG was created by means of the important role of trimethylaluminum, Me3Al, as a reducing agent for STO during LAO and YAO ALD as well as the Al2O3 ALD process at 300 °C. The deposited oxide layer also plays an essential role as a catalyst that enables Me3Al to reduce...

Extremely low surface recombination velocities in black silicon passivated by atomic layer deposition

Abstract: We investigate the optical and opto-electronic properties of black silicon (b-Si) nanostructures passivated with Al2O3. The b-Si nanostructures significantly improve the absorption of silicon due to superior anti-reflection and light trapping properties. By coating the b-Si nanostructures with a conformal layer of Al2O3 by atomic layer deposition, the surface recombination velocity can be effectively reduced. We show that control of plasma-induced subsurface damage is equally important to achieve low interface recombination. Surface recombination velocities of Seff<13 cm/s have been measured for an optimized structure which, like the polished reference, exhibits lifetimes in the millisecond range.

Method for Forming Dielectric Film Containing Si-C bonds by Atomic Layer Deposition Using Precursor Containing Si-C-Si bond

Abstract: A method of forming a dielectric film having Si—C bonds on a semiconductor substrate by atomic layer deposition (ALD), includes: (i) adsorbing a precursor on a surface of a substrate; (ii) reacting the adsorbed precursor and a reactant gas on the surface; and (iii) repeating steps (i) and (ii) to form a dielectric film having at least Si—C bonds on the substrate. The precursor has a Si—C—Si bond in its molecule, and the reactant gas is oxygen-free and halogen-free and is constituted by at least a rare gas.

Method for Forming Insulation Film Using Non-Halide Precursor Having Four or More Silicons

Abstract: A method of forming an insulation film on a semiconductor substrate by plasma enhanced atomic layer deposition (PEALD), includes: (i) adsorbing a non-excited non-halide precursor having four or more silicon atoms in its molecule onto a substrate placed in a reaction space; (ii) supplying an oxygen-free reactant to the reaction space without applying RF power so as to expose the precursor-adsorbed substrate to the reactant; and (iii) after step (ii), applying RF power to the reaction space while the oxygen-free reactant is supplied in the reaction space; and (iv) repeating steps (i) to (iii) as a cycle, thereby depositing an insulation film on the substrate