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High-quality dielectric films could enable GaN normally off high-electron-mobility transistors (HEMTs). Plasma atomic layer deposition (ALD) is known to allow for controlled high-quality thin-film deposition, and in order to not exceed energy and flux levels leading to device damage, the plasma used should preferably be remote for many applications. This article outlines ion energy flux distribution functions and flux levels for a new remote plasma ALD system, Oxford Instruments Atomfab™, which includes an innovative, RF-driven, remote plasma source. The source design is optimized for ALD for GaN HEMTs for substrates up to 200 mm in diameter and allows for Al2O3 ALD cycles of less than 1 s. Modest ion energies of

The deposition of dielectric materials on graphene is one of the bottlenecks for unlocking the potential of graphene in electronic applications. In this paper we demonstrate the plasma enhanced atomic layer deposition of 10 nm thin high quality Al$_2$O$_3$ on graphene using a monolayer of hBN as protection layer. Raman spectroscopy was performed to analyze possible structural changes of the graphene lattice caused by the plasma deposition. The results show that a monolayer of hBN in combination with an optimized deposition process can effectively protect graphene from damage, while significant damage was observed without an hBN layer. Electrical characterization of double gated graphene field effect devices confirms that the graphene did not degrade during the plasma deposition of Al$_2$O$_3$. The leakage current densities were consistently below 1 nA/mm for electric fields across the insulators of up to 8 MV/cm, with irreversible breakdown happening above. Such breakdown electric fields are typical for Al$_2$O$_3$ and can be seen as an indicator for high quality dielectric films.

Microchannel plates (MCPs) have been used for many years in space flight instrumentation as fast, lightweight electron multipliers. A new MCP fabrication method combines a glass substrate composed of hollow glass capillary arrays (GCAs) with thin film coatings to provide the resistive and secondary electron emissive properties. Using this technique, the gain, resistance and glass properties may be chosen independently. Large area MCPs are available at moderate cost. Secondary emission films of Al2O3 and MgO provide sustained high gain as charge is extracted from the MCP. Long lifetimes are possible, and a total extracted charge of 7 C/cm2 has been demonstrated. Background rates are low because the glass substrate has little radioactive potassium 40. Curved MCPs are easily fabricated with this technique to suit instrument symmetries, simplifying secondary electron steering and smoothing azimuthal efficiency.

Spectral analysis of optically excited currents in single-crystal (100)InAs/amorphous (a-)Al2O3/ metal structures allows one to separate contributions stemming from the internal photoemission (IPE) of electrons into alumina and from the trapping-related displacement currents. IPE spectra suggest that the out-diffusion of In and, possibly, its incorporation in a-Al2O3 lead to the development of 0.4 eV wide conduction band (CB) tail states. The top of the InAs valence band is found at 3.4560.10 eV below the alumina CB bottom, i.e., at the same energy as at the GaAs/a-Al2O3 interface. This corresponds to the CB and the valence band offsets at the InAs/a-Al2O3 interface of 3.160.1 eV and 2.560.1 eV, respectively. However, atomic-layer deposition of alumina on InAs results in additional low-energy electron transitions with spectral thresholds in the range of 2.0–2.2 eV, which is close to the bandgap of AlAs. The latter suggests the interaction of As with Al, leading to an interlayer containing Al-As bonds providing a lower barrier for electron injection. received: 2016-09-05 accepted: 2016-11-17 published: 2016-12-15 ispartof: Journal of Applied Physics vol:120 issue:23 pages:235701-1 status: published

Bundles of hollow glass capillaries can be tapered to produce quasi-focusing x-ray optics. These optics are known as Kumakhov lenses. These optics are interesting for lab-based sources because they can be used to collimate and concentrate x-rays originating from a point, such as a laser focus or an electron-beam focus in a microtube.

We describe the synthesis, characterization, and application of nanocomposite, tunable resistance coatings consisting of conducting, metallic nanoparticles embedded in an amorphous dielectric matrix. These films are comprised of M:Al2O3 with M=Mo or W, and are prepared by atomic layer deposition (ALD) using alternating exposures to trimethyl aluminum and H2O for the Al2O3 ALD and alternating MF6/Si2H6 exposures for the metal ALD. By varying the ratio of ALD cycles for the metal and the Al2O3 components in the film, we can tune precisely the resistance of these coatings over a very broad range from 105-1012 Ohm.cm. These films exhibit ohmic behavior and resist breakdown even at high electric fields of 107 V/m. Moreover, the self-limiting nature of ALD allows us to grow these films inside of porous substrates and on complex 3D surfaces. As a result of these qualities, our nanocomposite films have proved exceptional as resistive coatings in microchannel plate electron multipliers and as charge drain coatings in electron-optical devices.

The increasing availability of small satellites such as CubeSats have improved low cost access to space. New scientific measurements may be made, and new concepts may be tested for larger scale missions in the future. Particle detection instruments in conventional size spacecraft have to meet significant constraints on mass, power and volume. These constraints are more substantial in the CubeSat platform. Microchannel plate (MCP) electron multipliers are frequently used in particle detection instruments because of their high gain, low mass, and thin planar configuration. However, non-planar MCPs can be used to improve instrument performance and make better use of available volume by adopting a shape that is compatible with the natural instrument geometry. Non-planar MCPs have been made in this work using a novel method, in which a glass microchannel substrate is coated with thin films that provide the necessary resistive and secondary electron emissive properties. The glass substrates were first slumped at a high temperature to a mandrel of the desired shape, after which the thin films were applied. The MCPs were cylindrically curved, with radii of curvature of 75 mm and 20 mm, and with angular spans of 90 degrees and 180 degrees respectively. The azimuthal gain and resistance uniformity was measured and will be presented.

Very large (20 cm × 20 cm) flat panel phototubes are being developed which employ novel microchannel plates (MCPs). The MCPs are manufactured using borosilicate microcapillary arrays which are functionalized by the application of resistive and secondary emissive layers using atomic layer deposition (ALD). This allows the operational parameters to be set by tailoring sequential ALD deposition processes. The borosilicate substrates are robust, including the ability to be produced in large formats (20 cm square). ALD MCPs have performance characteristics (gain, pulse amplitude distributions, and imaging) that are equivalent or better than conventional MCPs. They have low intrinsic background (0.045 events cm-2 sec-1)., high open area ratios (74% for the latest generation of borosilicate substrates), and stable gain during >7 C cm-2 charge extraction after preconditioning (vacuum bake and burn-in). The tube assemblies use a pair of 20 cm × 20 cm ALD MCPs comprised of a borosilicate entrance window, a proximity focused bialkali photocathode, and a strip-line readout anode. The second generation design employs an all glass body with a hot indium seal and a transfer photocathode. We have achieved >20% quantum efficiency and good gain uniformity over the 400 cm2 field of view, spatial resolution of

This work focuses on the development of novel nano-engineered microchannel plates (MCPs) to enhance a new generation of NUV-visible light photon counting detectors that have a wide range of applications in LIDAR, 3D topographic imaging, high-speed photography, bio-medial fluorescence microscopy and astronomical imaging. The MCPs are borosilicate glass micro-capillary arrays functionalized using atomic layer deposition (ALD). MCP's manufactured in this way have many advantageous properties, including the ability to withstand high processing temperatures, high secondary electron yield, and low outgassing. This scheme has the ability to support higher global photon count rates while greatly reducing the deterioration of photocathode efficiency and detector gain. Opaque photocathodes have been deposited onto these nano-engineered borosilicate MCPs and several sealed tube devices have been constructed. Here we report on the progress of this effort, including performance and lifetime characteristics from the sealed tubes and MCPs, and results from the deposition of opaque photocathodes onto nano-engineered MCPs.

Novel borosilicate microcapillary array MCPs have been employed build large area (20 cm × 20 cm) flat panel phototube detectors. Design of the 20 cm sealed tube assembly comprises of a borosilicate entrance window, a proximity focused bialkali photocathode, a pair of MCPs, and a strip-line readout anode. Micro-capillary arrays have been processed to function as microchannel plates (MCPs) using atomic layer deposition (ALD) to produce the conductive and secondary emissive layers. Using borosilicate micro-capillary substrates has advantages over traditional MCPs, including the ability to be produced in large robust formats (20cm), low intrinsic background ( 7 C cm−2 charge extraction after preconditioning (vacuum bake and burn-in). The gain, pulse height distribution, imaging performance are equivalent, or better than conventional MCPs. The flat panel design employs a brazed ceramic walled enclosure with a hot indium seal and a transfer photocathode. We have achieved >20% quantum efficiency and good gain uniformity over the 20cm field of view, spatial resolution of

International audience; We describe the formation of RuO 2 thin films grown using atomic layer deposition (ALD) on (100) Si substrates from Ru(EtCp) 2 and O 2 , and the subsequent influence of annealing temperature and atmosphere on the surface morphology and structure of the deposited layers. The films are characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction (ED). The as-deposited films consist of RuO 2 islands. No significant changes in composition or morphology are observed following annealing in N 2 for 4 h at either 500 or 7008C. Higher temperature annealing in N 2 (8208C, 4 h) results in some modifications to the morphology and structure where ED data indicate the formation of some Ru metal. However, complete transformation from as-deposited RuO 2 to Ru metal is, obtained after annealing in forming gas (95% N 2 /5% H 2) at 4208C for 5 min.

In this work we present the results of a combined experimental and theoretical investigation into the capacitance-voltage characteristics of the high-k/In0.53Ga0.47As/InP system. The emphasis of the work is placed on the maximum measured and theoretical capacitance for n and p doped In0.53Ga0.47As epitaxial layers. Theoretical calculations based on ideal systems indicate a highly asymmetric CV response, with an equivalent oxide thickness correction ~ 1.4nm (Γ valley only) and ~ 0.23nm for the high-k/n-In0.53Ga0.47As/InP and high-k/p-In0.53Ga0.47As/InP systems respectively. The theoretical calculations are compared to experimental results for Al2O3 /In0.53Ga0.47As/InP MOS structures, and discrepancies are discussed.

Control of the high-k/III-V interface by deposition of thin (~1-2 nm) interface control layers (ICLs) of Al2O3 or MgO, as part of an overall bi-layer structure with a high-k metal oxide MO2 (M = Hf|Zr), is explored. An Al2O3 or MgO ICL is deposited on unpassivated InxGa1-xAs (x = 0|0.53) substrates prior to MO2 gate oxide deposition, forming a Pd/high-k/ICL/III-V gate stack. The aim of a bi-layer structure is to enable continued device scaling using a high-k MO2 oxide while improving the high-k/III-V interface quality and interfacial band structure, with an Al2O3 or MgO ICL. Metal-oxide-semiconductor capacitor (MOSCAP) devices with an Al2O3 ICL on p-GaAs display significantly reduced leakage current density, and reduced frequency dispersion of accumulation capacitance when compared to a no-ICL device, indicating an improved high-k/III-V band structure and interface quality, respectively. Further studies on ZrO2/Al2O3/In0.53Ga0.47As devices find a reduced defect response with a post-metal forming gas anneal.

The focus of this paper is the application of Fourier transform infrared spectroscopy (FTIR) and near infrared-tuneable diode laser spectroscopy (NIR-TDLAS) as in situ tools to monitor the formation of gas phase products during atomic layer deposition (ALD). Two studies are chosen to highlight the importance of monitoring the gas phase, in this surface driven process, for both mechanistic and reactor dynamics considerations. The first study is the FTIR monitoring of the ALD of HfO2, from Hf[N(CH3)2]4 and H2O where it was found that, in addition to the expected HN(CH3)2, gas phase species were generated including CO, CH4 and HCN. The second ALD system investigated was the growth of Al2O3 from Al(CH3)3 and H2O employing NIR-TDLAS as a real time in situ probe to monitor the evolution of CH4.

The quality of the high-k/InxGa1-xAs interface is a crucial factor in achieving high electron mobility compound semiconductor field effect transistors. Capacitance and conductance characterisation methods were employed to evaluate different high-k/InGaAs interfaces. This paper will first discuss the specificity of capacitance voltage characteristics of compound semiconductor MOS structures, and then the recent progress in the study of high k/InxGa1 xAs interfaces will be presented. The capacitance and conductance measurements are combined to provide a picture of the interface state density. We have also investigated the merit of using intermediate k value dielectrics such as Al2O3 and MgO as interface control layers between the semiconductor and the main high k layer.

The electron energy band alignment at interfaces of In x Ga 1− x As (0 ⩽ x ⩽ 0.53) with atomic-layer deposited insulators Al 2 O 3 and HfO 2 is characterized using combined measurements of internal photoemission of electrons and photoconductivity. The measured energy of the In x Ga 1− x As valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the observed bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. Electron states originating from the interfacial oxidation of In x Ga 1− x As lead to reduction of the electron barrier at the semiconductor/oxide interface.

The monitoring of chemical vapour deposition, and its variant atomic layer deposition, by in-situ spectroscopic methods is well established and has been used to elucidate many important details of the dynamics, kinetics and mechanisms of these complex processes. Here we examine two in-situ gas phase probes that we have been employing, firstly, Fourier transform mid and near-infrared spectroscopy to elucidate the nature of the gas phase products, and secondly, the use of near infrared tunable diode laser spectroscopy to spatially and temporally resolve the spectral features due to either reactants or products. Data is presented for the i) Al2O3 from Al(CH3)3 and H2O and; ii) HfO2 from Hf(N(CH3)2)4 and H2O growth systems.

We demonstrate that mesoporous silica particles capable of acting as receptacles for functional nanoparticles may be readily synthesized and then assembled into photonic crystal thin films displaying well-defined Bragg diffraction features in the visible region. We show that it is possible to tailor not only the particle diameter, but also the pore diameters within the particles. As an example of the possible application of such particles in photonic crystal fabrication we show that it is possible to deposit Fe 2 O 3 nanoparticles on the exterior of and inside the pores of hexagonal phase mesoporous silica spheres.

A new spectrometer design that will result in a highly efficient, easy to handle, low-cost, high-resolution spectroscopy system with excellent background suppression is being developed for the NSLS-II Inner-Shell Spectroscopy beamline. This system utilizes non-diffractive optics comprised of fused and directed glass capillary tubes that will be used to collect and pre-collimate fluorescence photons. There are several advantages enabled by this design; a large energy range is accessible without modifying the s-stem, a large collection angle is achieved per detection unit: 4-5% of the full solid angle, easy integration in complex and harsh environments is enabled due to the use of a pre-collimation system as a secondary source for the spectrometer, and background from a complex sample environment can be easily and efficiently suppressed. The polycapillary X-ray focusing optics segment of this application has been under development. This includes improvement in manufacturing methods of polycapillary structure for x-ray optics, forming the polycapillary structure to produce X-ray optics to achieve the required solid angle collection and transmission efficiency, and measurement of X-ray focusing properties of the optics using an X-ray source. Two promising advances are large open area ratios of 80% or more, and the possibility of adding coatings in the capillaries using Atomic Layer Deposition techniques to improve reflection efficiency.

Borosilicate microcapillary arrays have been functionalized by Atomic Layer Deposition (ALD) of resistive and secondary emissive layers to produce robust microchannel plates (MCPs) with improved performance characteristics over traditional MCPs. These techniques produce MCP’s with enhanced stability and lifetime, low background rates, and low levels of adsorbed gas. Using ALD to functionalize the substrate decouples the two and provides the opportunity to explore many new materials. The borosilicate substrates have many advantages over traditional lead glass MCPs, including the ability to be fabricated in large areas (currently at 400 cm2).

Manufacturing plans for “next generation” microchannel plates (MCPs) and the technical advantages enabled by this evolving technology are presented. The Large Area Picosecond Photodetector (LAPPD) is an MCP based photodetector, capable of imaging, with high spatial and temporal resolution in a hermetic package with an active area of 400 square centimeters. A key component of LAPPD is a chevron pair of large area (20 x 20 cm) MCPs. The manufacture of these large-area high performance MCPs has been enabled by the convergence of two technological breakthroughs. The first is the ability to produce large blocks of hollow, micronsized glass capillary arrays (GCAs) developed by Incom Inc. The Incom process is based on the use of an etchless “hollow-core” approach in the glass drawing process, eliminating the need to remove core material by chemical etching. The arrays are fabricated as large blocks that can be sliced to form large area wafers, without regard to the conventional limits of L/d (capillary length / pore diameter). Moreover, the glass used in these GCAs is physically more robust, does not have a tendency to warp, and has low levels of radioactive isotopes resulting in low dark noise. The second breakthrough is the advent of atomic layer deposition (ALD) coating methods and materials to functionalize GCAs to impart the necessary resistive and secondary emission properties suitable for large area detector applications. Recent results demonstrating the high performance, uniformity, and long term stability of the current MCP product are presented.

The technique of atomic layer deposition (ALD) has enabled the development of alternative glass microchannel plates (MCPs) with independently tunable resistive and emissive layers, resulting in excellent thickness uniformity across the large area (20 × 20 cm), high aspect ratio (60:1 L/d) glass substrates. Furthermore, the use of ALD to deposit functional layers allows the optimal substrate material to be selected, such as borosilicate glass, which has many benefits compared to the lead-oxide glass used in conventional MCPs, including increased stability and lifetime, low background noise, mechanical robustness, and larger area (at present up to 400 cm2). Resistively stable, high gain MCPs are demonstrated due to the deposition of uniform ALD resistive and emissive layers on alternative glass microcapillary substrates. The MCP performance characteristics reported include increased stability and lifetime, low background noise (0.04 events cm−2 s−1), and low gain variation (±5%).

High mobility III-V substrates with high-k oxides are required for device scaling without loss of channel mobility. Interest has focused on the self-cleaning effect on selected III-V substrates during atomic layer deposition of Al2O3. A thin (similar to 1 nm) Al2O3 interface control layer is deposited on In0.53Ga0.47As prior to HfO2 growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by similar to 50% while maintaining scaling trends. Significant reductions in leakage current density and increased breakdown voltage are found, indicative of a band structure improvement due to the reduction/removal of the In0.53Ga0.47As native oxides. (C) 2010 American Institute of Physics. (doi: 10.1063/1.3473773)

7th International Symposium on High Dielectric Constant Materials and Gate Stacks - 216th Meeting of the Electrochemical Society; Vienna; Austria; 5 October 2009 through 7 October 2009; Code 79118 In this work results are presented of an investigation into the structural and electrical properties of HfO2 films on GaAs and InxGa1-xAs substrates for x: 0.15, 0.30, and 0.53. The capacitancevoltage responses of the GaAs and InxGa1-xAs (x: 0.15 and 0.30) are dominated by an interface defect response. Analysis of these samples at 77K indicates that the defect density is > 2.5x1013 cm-2. For the HfO2/In0.53Ga0.47As system, 77K capacitance-voltage responses indicate surface accumulation is achieved. The results are consistent with a high defect density, with an energy level {greater than or equal to}0.75 eV above the valence band in the HfO2/InxGa1-xAs system, where the defect energy with respect to the valence band, does not change with the composition of the InxGa1-xAs. The HfO2/In0.53Ga0.47As interface exhibits two defects at 0.3eV (1.7x1013cm-2eV) and 0.61eV (1.5x1013cm-2eV) above the valance band edge. The defect at 0.61eV is removed by forming gas annealing at 325oC.

Band alignment at the interfaces of (100)GaAs with Al2O3 and HfO2 grown using atomic layer deposition is determined using internal photoemission and photoconductivity measurements. Though the inferred conduction and valence band offsets for both insulators were found to be close to or larger than 2 eV, the interlayer grown by concomitant oxidation of GaAs reduces the barrier for electrons by approximately 1 eV. The latter may pose significant problems associated with electron injection from GaAs into the oxide. (C) 2008 American Institute of Physics. (DOI: 10.1063/1.3021374)

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The atomic layer deposition of high dielectric constant oxides like HfO2 on III-V substrates such as In0.53Ga0.47As leads to a poor interface, with the growth of In0.53Ga0.47As native oxides regardless of the surface pretreatment and passivation method. The presence of the native oxides leads to poor gate leakage current characteristics due to the low band gap of the native oxides and the presence of potential wells at the interface. In addition, the poor quality of this interface leads to very large interface state defect densities, which are detrimental to metal-oxide-semiconductor-based device performance. A wide band gap interlayer replacing the native oxide layer would remove the potential wells and provide a larger barrier to conduction. It may also assist in the improvement of the interface quality, but the problem remains as to how this native oxide interlayer cannot only be removed but prevented from regrowing. In this regard, the authors present electrical results showing that the atomic layer d...

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The electron energy band alignment at interfaces of InxGa1-xAs (0

Electrical properties of metal-oxide-semiconductor capacitors using atomic layer deposited HfO2 on n-type GaAs or InxGa1-xAs (x=0.53, 0.30, 0.15) epitaxial layers were investigated. Capacitance-voltage (CV) measurements indicated large temperature and frequency dispersion at positive gate bias in devices using n-type GaAs and low In content (x=0.30, 0.15) InxGa1-xAs layers, which is significantly reduced for devices using In0.53Ga0.47As. For In0.53Ga0.47As devices, the CV response at negative gate bias is most likely characteristic of an interface state response and may not be indicative of true inversion. The conductance technique on Pd/HfO2/In0.53Ga0.47As/InP shows reductions in interface state densities by In0.53Ga0.47As surface passivation and forming gas annealing (325 degrees C). (C) 2009 American Institute of Physics. (DOI: 10.1063/1.3089688)

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