Publications

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    ABSTRACT: Nanocomposite films were successfully grown by aerosol-assisted chemical vapour deposition (CVD) in a single deposition step using a mixture of Indium Tin neodecanoate and ligand stabilised silicon nanocrystals. Samples were analysed by HRTEM and silicon nanocrystals with a density of 1.2 × 10 12 cm-2 were observed. From the reconstructed 3D tomogram, the averaged distance between the nearest nanoparticles is 8.3 nm and the 3D density of nanoparticles is 1.6 × 10 18 cm-3. An animation of the 3D reconstruction is supplied in the supporting information. These data show the versatility of aerosol assisted CVD in achieving a nanocomposite with such a density of silicon nanocrystals, of carefully controlled size and shape, within a polycrystalline host matrix. Therefore, meeting the density and size distribution requirements of particle inclusion in active nanocomposites for photovoltaic structures
    Journal of Sol-Gel Science and Technology 01/2015; 73(3):1-7. DOI:10.1007/s10971-015-3618-3 · 1.55 Impact Factor
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    ABSTRACT: The authors report on the structural and electrical properties of TiN/Al2O3/TiN metal–insulator–metal (MIM) capacitor structures in submicron three-dimensional (3D) trench geometries with an aspect ratio of ∼30. A simplified process route was employed where the three layers for the MIM stack were deposited using atomic layer deposition (ALD) in a single run at a process temperature of 250 °C. The TiN top and bottom electrodes were deposited via plasma-enhanced ALD using a tetrakis(dimethylamino)titanium precursor. 3D trench devices yielded capacitance densities of 36 fF/μm2 and quality factors >65 at low frequency (200 Hz), with low leakage current densities (<3 nA/cm2 at 1 V). These devices also show strong optical iridescence which, when combined with the covert embedded capacitance, show potential for system in package (SiP) anticounterfeiting applications.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2015; 33(1):01A103-01A103-5. DOI:10.1116/1.4891319 · 2.14 Impact Factor
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    ABSTRACT: The aerosol assisted chemical vapor deposition of monoclinic vanadium pentoxide coatings was performed on fluorine doped tin dioxide coated glass substrates using vanadyl(IV) acetylacetonate at 400 1C for a range of growth periods. It was observed that the sample grown for 1 h presented the best electrochemical response in terms of the highest charge storage (30 mC cm À 2) and the difference in transmittance in the visible and near-infrared spectral regions (27% at 650 nm and 17% at 900 nm) with a fast response time (12 s for coloration and 10 s for bleaching). The importance of achieving samples with (2 0 0) preferred orientation for the improvement of electrochromic performance is highlighted. &
    Solar Energy Materials and Solar Cells 12/2014; DOI:10.1016/j.solmat.2014.12.002 · 5.03 Impact Factor
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    ABSTRACT: Experimental observations for the In0.53Ga0.47As metal-oxide-semiconductor (MOS) system in inversion indicate that the measured capacitance (C) and conductance (G or Gm), are uniquely related through two functions of the alternating current angular frequency (ω). The peak value of the first function (G/ω) is equal to the peak value of the second function (-dC/dloge(ω) ≡ -ωdC/dω). Moreover, these peak values occur at the same angular frequency (ωm), that is, the transition frequency. The experimental observations are confirmed by physics-based simulations, and applying the equivalent circuit model for the MOS system in inversion, the functional relationship is also demonstrated mathematically and shown to be generally true for any MOS system in inversion. The functional relationship permits the discrimination between high interface state densities and genuine surface inversion. The two function peak values are found to be equal to Cox2/(2(Cox + CD)) where Cox is the oxide capacitance per unit area and CD is the semiconductor depletion capacitance in inversion. The equal peak values of the functions, and their observed symmetry relation about ωm on a logarithmic ω plot, opens a new route to experimentally determining Cox. Finally, knowing ωm permits the extraction of the minority carrier generation lifetime in the bulk of the In0.53Ga0.47As layer.
    IEEE Transactions on Electron Devices 12/2014; 61(12):4176-4185. DOI:10.1109/TED.2014.2362524 · 2.36 Impact Factor
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    ABSTRACT: The metal-organic Cu(I) complex 1,3-diisopropyl-imidazolin-2-ylidene copper hexamethyl disilazide has been tested as a novel oxygen-free precursor for atomic layer deposition of Cu with molecular hydrogen. Being a strong Lewis base, the carbene stabilizes the metal centre to form a monomeric compound that can be vaporised and transported without visible degradation. A significant substrate dependence of the growth process not only with respect to the film material but also to the structure of the films was observed. On Pd surfaces continuous films are grown and no phase boundary can be observed between the Cu film and the Pd, while island growth is observed on Ru substrates, which as a consequence requires thicker films in order to achieve a fully coalesced layer. Island growth is also observed for ultra-thin (<10 nm) Pd layers on Si substrates. Possible explanations for the different growth modes observed are discussed.
    09/2014; 2(43). DOI:10.1039/C4TC01418A
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    ABSTRACT: Capacitance-Voltage (C-V) characterization and hard x-ray photoelectron spectroscopy (HAXPES) measurements have been used to study metal/Al2O3/In0.53Ga0.47As capacitor structures with high (Ni) and low (Al) work function metals. The HAXPES measurements observe a band bending occurring prior to metal deposition, which is attributed to a combination of fixed oxide charges and interface states of donor-type. Following metal deposition, the Fermi level positions at the Al2O3/In0.53Ga0.47As interface move towards the expected direction as observed from HAXPES measurements. The In0.53Ga0.47As surface Fermi level positions determined from both the C-V analysis at zero gate bias and HAXPES measurements are in reasonable agreement. The results are consistent with the presence of electrically active interface states at the Al2O3/In0.53Ga0.47As interface and suggest an interface state density increasing towards the In0.53Ga0.47As valence band edge.
    Journal of Applied Physics 07/2014; 116(2):024104. DOI:10.1063/1.4887517 · 2.19 Impact Factor
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    ABSTRACT: A design of experiments methodology was used to optimize the sheet resistance of titanium nitride (TiN) films produced by plasma-enhanced atomic layer deposition (PE-ALD) using a tetrakis(dimethylamino)titanium precursor in a N2/H2 plasma at low temperature (250 °C). At fixed chamber pressure (300 mTorr) and plasma power (300 W), the plasma duration and N2 flow rate were the most significant factors. The lowest sheet resistance values (163 Ω/sq. for a 20 nm TiN film) were obtained using plasma durations ∼40 s, N2 flow rates >60 standard cubic centimeters per minute, and purge times ∼60 s. Time of flight secondary ion mass spectroscopy data revealed reduced levels of carbon contaminants in the TiN films with lowest sheet resistance (163 Ω/sq.), compared to films with higher sheet resistance (400–600 Ω/sq.) while transmission electron microscopy data showed a higher density of nanocrystallites in the low-resistance films. Further significant reductions in sheet resistance, from 163 Ω/sq. to 70 Ω/sq. for a 20 nm TiN film (corresponding resistivity ∼145 μΩ·cm), were achieved by addition of a postcycle Ar/N2 plasma step in the PE-ALD process.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 05/2014; 32(3):031506-031506-6. DOI:10.1116/1.4868215 · 2.14 Impact Factor
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    ABSTRACT: Combined in situ IR measurements and first-principles calculations of InP(100) surfaces reveal that mild annealing (300 °C), typically needed for atomic layer deposition, leads to the formation of InP-derived surface hydrophosphate species (both P═O and P–OH sites). The initial interaction of trimethylaluminum at 300 °C results in the formation of P–O–Al linkages through covalent and dative bonding by reaction with surface hydroxyls. During subsequent ALD cycles to deposit Al2O3, an interfacial layer composed of P–O–Al bonds (1140 cm–1) is formed, requiring approximately seven cycles for completion. Similar chemical transformations are observed on hydrofluoric acid and ammonium-sulfide treated [HF/(NH4)2S] surfaces but to a lesser degree since the oxide thickness is reduced, requiring only approximately three cycles to fully complete the interfacial layer. Initially, the ALD growth of Al2O3 is slower on the HF/(NH4)2S-treated InP(100) surface than on the native oxide surface due to a lower density of hydroxyl groups. However, this slow growth leads to a denser film, highlighting the importance of the chemical composition of the initial InP(100) substrate.
    The Journal of Physical Chemistry C 03/2014; 118(11):5862–5871. DOI:10.1021/jp412455y · 4.84 Impact Factor
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    ABSTRACT: A method which combines polymer particle assembly, chemical infiltration and etching with an aerosol assisted deposition process is described for the fabrication of 3D inverse opal (IO) structures with sub-micron periodicity and precision. This procedure not only overcomes limitations associated with slow, expensive micro-fabrication methods but also permits the tuning of refractive index contrast via the direct incorporation of photonically-active, preformed, tailored silicon nanostructures. It is demonstrated that this approach can be used to modify the photonic band gap (PBG) by effectively depositing/patterning optically active silicon nanocrystals (ncSi) onto the pore walls of a 3D inverse opal structure. This simple, yet effective method for preparing functional complex 3D structures has the potential to be used generically to fabricate a variety of functional porous 3D structures that could find application not only in new or improved photonic crystal (PC) devices but also in areas such as catalysis, separation, fuel cells technology, microelectronics and optoelectronics.
    02/2014; 2(9). DOI:10.1039/C3TC31994F
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    ABSTRACT: The junctionless nanowire metal–oxide–semiconductor field‐effect transistor (JNT) has recently been proposed as an alternative device for sub‐20‐nm nodes. The JNT architecture eliminates the need for forming PN junctions, resulting in simple processing and competitive electrical characteristics. In order to further boost the drive current, alternative channel materials such as III–V and Ge, have been proposed. In this Letter, JNTs with Ge channels have been fabricated by a CMOS‐compatible top–down process. The transistors exhibit the lowest subthreshold slope to date for JNT with Ge channels. The devices with a gate length of 3 μm exhibit a subthreshold slope (SS) of 216 mV/dec with an I ON/I OFF current ratio of 1.2 × 103 at V D = –1 V and drain‐induced‐barrier lowering (DIBL) of 87 mV. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) This Letter describes the fabrication of junctionless nanowire transistors (JNT) with Ge channel. The simplified process without forming PN juntions is very suitable for Ge, which is a promising channel material to boost the drain current. The fabricated transistors exhibit the lowest subthreshold slope to date for JNT with Ge channels. The devices with a gate length of 3 μm exhibit a subthreshold slope (SS) of 216 mV/dec with an I ON/I OFF current ratio of 1.2×103 at V D = –1 V and drain‐induced‐barrier‐lowing (DIBL) of 87 mV.
    physica status solidi (RRL) - Rapid Research Letters 01/2014; 8(1). DOI:10.1002/pssr.201300119 · 2.34 Impact Factor
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    ABSTRACT: Diffusion of indium through HfO2 after post deposition annealing in N2 or forming gas environments is observed in HfO2/In0.53Ga0.47As stacks by low energy ion scattering and X-ray photo electron spectroscopy and found to be consistent with changes in interface layer thickness observed by transmission electron microscopy. Prior to post processing, arsenic oxide is detected at the surface of atomic layer deposition-grown HfO2 and is desorbed upon annealing at 350 °C. Reduction of the interfacial layer thickness and potential densification of HfO2, resulting from indium diffusion upon annealing, is confirmed by an increase in capacitance.
    Applied Physics Letters 12/2013; 104(1). DOI:10.1063/1.4860960 · 3.52 Impact Factor
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  • 224th ECS Meeting; 10/2013
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    ABSTRACT: The growth of Cu films by atomic layer deposition using hydrogen plasma has been investigated. To obtain continuous films at sub 5 nm thicknesses the two dimensional coalescence of Cu nucleation sites formed at the start of the deposition process must be enhanced in preference to three dimensional island growth. Thermal energy reduction in the growth process is a key parameter. In this work hydrogen plasma is used to allow the reduction of the adsorbed precursor to metallic Cu at a range of low temperatures. Therefore, precursors can be compared at their low temperature limit, which is mainly determined by transport issues due to their relatively low vapor pressures. The structure of the deposited Cu films varies strongly with the substrate material used highlighting the importance of the nucleation mechanisms. On metallic substrates such as Ru and Pd continuous conductive thin films could be obtained, island formation and slow coalescence were observed on Si, TaN and CDO substrates even at temperatures low as 30 °C; therefore conductive films could only be obtained for relatively thick deposits.
    Surface and Coatings Technology 09/2013; 230:3 - 12. DOI:10.1016/j.surfcoat.2013.06.066 · 2.20 Impact Factor
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    ABSTRACT: In this work we present experimental results examining the energy distribution of the relatively high (>1 × 1012 cm−2 eV−1) density of electrically active defects which are commonly reported at the interface between high dielectric constant (high-k) thin films and In0.53Ga0.47As. The interface state distribution is examined for the Al2O3/In0.53Ga0.47As metal-oxide-semiconductor (MOS) system based on analysis of the full gate capacitance (Cg–Vg) of the surface n-channel In0.53Ga0.47As MOS transistors. The experimental capacitance, recorded at −50 °C and 1 MHz to approximate a high frequency response, is compared to the theoretical Cg–Vg response to evaluate the interface state distribution across the In0.53Ga0.47As energy gap and extending into the In0.53Ga0.47As conduction band. To improve the accuracy of the fitting process, the Maserjian Y-function was used in the modeling of the interface defects and fixed oxide charge densities. The analysis reveals a peak of donor-like interface traps with a density of 1.5 × 1013 cm−2 eV−1 located at ∼0.36 eV above the In0.53Ga0.47As valence band edge, a high density of donor-like states increasing towards the In0.53Ga0.47As valence band. The analysis also indicates acceptor-like interface traps located in the In0.53Ga0.47As conduction band, with a density of ∼2.5 × 1013 cm−2 eV−1 at 0.3 eV above the In0.53Ga0.47As conduction band minima. The reported interface state density is similar to reports for others oxides, suggesting that the recorded interface states originate from the In0.53Ga0.47As surface.
    Microelectronic Engineering 09/2013; 109:182–188. DOI:10.1016/j.mee.2013.03.026 · 1.34 Impact Factor
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    ABSTRACT: Future high energy astrophysics missions will require high performance novel X-ray optics to explore the Universe beyond the limits of the currently operating Chandra and Newton observatories. Innovative optics technologies are therefore being developed and matured by the European Space Agency (ESA) in collaboration with research institutions and industry, enabling leading-edge future science missions. Silicon Pore Optics (SPO) [1 to 21] and Slumped Glass Optics (SGO) [22 to 29] are lightweight high performance X-ray optics technologies being developed in Europe, driven by applications in observatory class high energy astrophysics missions, aiming at angular resolutions of 5” and providing effective areas of one or more square meters at a few keV. This paper reports on the development activities led by ESA, and the status of the SPO and SGO technologies, including progress on high performance multilayer reflective coatings [30 to 35]. In addition, the progress with the X-ray test facilities and associated beam-lines is discussed [36].
    Optics for EUV, X-Ray, and Gamma-Ray Astronomy VI, San Diego; 08/2013
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    ABSTRACT: The junctionless device concept for silicon-on-insulator MOSFETs was introduced by Colinge et al. in 2010 [1], demonstrating considerable gains in terms of process simplicity when compared to conventional inversion-mode MOSFETs. The objective of this work is to implement the junctionless device concept in an In0.53Ga0.47As channel, where the SiO2 insulator in [1] is replaced by a wide bandgap In0.52Al0.48As barrier layer. The junctionless device architecture is particularly well suited to III-V channel materials. Firstly, the high doping concentration (Nd) present in the channel of a junctionless MOSFET is less problematic for In0.53Ga0.47As than it is for Si. Indeed, the bulk electron mobility in Si is ~100 cm2/V.s at Nd = 1 × 1019 /cm3 [2], while that in In0.53Ga0.47As is ~4,000 cm2/V.s at a similar Nd level [3]. Moreover, the junctionless architecture circumvents the difficulties associated with the implantation [4] or regrowth [5] techniques generally used to form the source/drain (S/D) regions of III-V inversion-mode MOSFETs.
    2013 71st Annual Device Research Conference (DRC); 06/2013
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    Microelectronic Engineering 01/2013; · 1.34 Impact Factor

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