[Show abstract][Hide abstract] ABSTRACT: We report on a method to enhance the light-emission efficiency of printable thin films of a polymer doped with luminescent (CdSe)ZnS nanocrystals via metallic nanoparticles and nanoimprinted photonic crystals. We experimentally show a strong fluorescence enhancement of nanocrystals by coupling exciton-plasmon with the localized surface plasmon of metallic nanoparticles. The emitted light is efficiently diffracted by photonic crystals structures directly imprinted in the nanocomposite polymer. By combining the field susceptibility technique with optical Bloch equations, we examine the interaction of the quantum and plasmonic entities at small distances.
[Show abstract][Hide abstract] ABSTRACT: We present a systematic study of Si dopant implantation and activation in p-type In0.53Ga0.47As in an attempt to optimize the source and drain regions of an n-channel III-V metal–oxide–semiconductor field-effect transistor. Test structures based on the transfer length method were fabricated on Si-implanted p-In0.53Ga0.47As/p-InP buffer/semi-insulting InP. A Doehlert design of experiment (DOE) was used to investigate the effect of annealing temperature and time on the electrical properties of the samples. The DOE covered an experimental domain of 625–725 °C and 15–45 s. The current–voltage characteristics of all tested structures exhibited excellent ohmic behavior. The DOE revealed a minimum sheet resistance of (195.6 ± 3.4) Ω/□ for an optimum anneal condition of 715 °C for 32 s. Nonalloyed Au/Ge/Au/Ni/Au contacts, on the sample annealed at 675 °C for 30 s (center point of the experimental domain), exhibited a low specific contact resistance of (7.4 ± 4.5) × 10−7 Ω cm2. The sample annealed at 675 °C for 30 s was further investigated using secondary ion mass spectrometry (SIMS) and cross-sectional transmission electron microscopy (XTEM) analyses. SIMS revealed that Si ions did not diffuse with annealing, while XTEM showed the formation of characteristic loop defects potentially responsible for the sheet resistance and specific contact resistance degradation.
No preview · Article · Aug 2012 · Semiconductor Science and Technology
[Show abstract][Hide abstract] ABSTRACT: We report on experimental observations of room temperature low frequency capacitance-voltage (CV) behaviour in metal oxide semiconductor (MOS) capacitors incorporating high dielectric constant (high-k) gate oxides, measured at ac signal frequencies (2 kHz to 1 MHz), where a low frequency response is not typically expected for Si or GaAs MOS devices. An analysis of the inversion regions of the CV characteristics as a function of area and ac signal frequency for both n and p doped Si and GaAs substrates indicates that the source of the low frequency CV response is an inversion of the semiconductor/high-k interface in the peripheral regions outside the area defined by the metal gate electrode, which is caused by charge in the high-k oxide and/or residual charge on the high-k oxide surface. This effect is reported for MOS capacitors incorporating either MgO or GdSiOx as the high-k layers on Si and also for Al2O3 layers on GaAs(111B). In the case of NiSi/MgO/Si structures, a low frequency CV response is observed on the p-type devices, but is absent in the n-type devices, consistent with positive charge (>8 x 10(10) cm(-2)) on the MgO oxide surface. In the case of the TiN/GdSiOx/Si structures, the peripheral inversion effect is observed for n-type devices, in this case confirmed by the absence of such effects on the p-type devices. Finally, for the case of Au/Ni/Al2O3/GaAs(111B) structures, a low-frequency CV response is observed for n-type devices only, indicating that negative charge (> 3 x 10(12) cm(-2)) on the surface or in the bulk of the oxide is responsible for the peripheral inversion effect. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4729331]
Full-text · Article · Jun 2012 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Hafnium erbium oxide (HfErOx) thin films were formed using atomic layer deposition. The effect of using different Hf:Er pulse ratios on the electrical and structural properties of the HfErOx thin films (∼9 nm) in metal–insulator–metal (MIM) capacitor structures have been investigated and comparisons made between as-deposited and annealed samples. We report the stabilisation of the higher dielectric constant (k) tetragonal/cubic phase by optimising the Hf:Er pulse ratio. The dielectric properties post thermal anneal at 500 °C were studied. A leakage current in the order of ∼1 × 10−8 (A/cm2) at a voltage of 1 V and a capacitance equivalent thickness of ∼1.4 nm have been achieved post thermal annealing at 500 °C.
No preview · Article · Jun 2012 · Microelectronic Engineering
[Show abstract][Hide abstract] ABSTRACT: Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces.
[Show abstract][Hide abstract] ABSTRACT: Electron energy-loss spectroscopy (EELS) is used to study the B distribution in a p-i-n layered solar cell structure. The boron concentration in the p-doped Si layer is expected to be ∼1021 cm−3 and should not exceed 1017 cm−3 in the neighbouring intrinsic layer. We show that B concentrations as low as 3×l020 cm−3 (0.6 at. %) can be measured using EELS. Our measurements are in close agreement with real space ab-initio multiple scattering calculations and secondary ion mass spectrometry measurements.
Full-text · Article · Nov 2011 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: Bright-field (BF) and annular dark-field (ADF) electron tomography in
the transmission electron microscope (TEM) are used to characterize
elongated porous regions or cracks (simply referred to as cracks
thereafter) in micro-crystalline silicon (μc-Si:H) solar cell. The
limitations of inferring the 3D geometry of a crack from a tilt series
of images acquired from 100-nm-thick focused ion beam (FTB) milled TEM
specimen are discussed. In an attempt to maximize the specimen tilt
range and to reduce the effects of diffraction and phase contrast on the
reconstruction, both BF and ADF electron tomography are used to acquire
360° tilt series of images from a FIB-prepared needle-shaped
Full-text · Article · Nov 2011 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: The oxidation behaviour of 10Cr and 20Cr iron alloys, with nickel contents from 0 to 34 wt% both in air and in CO/CO2, is summarized with particular emphasis on the form and chemistry of the different scales as they were observed using transmission electron microscopy. The various modes of inward oxidation are for example characterized with ‘internal’ and ‘inner’ oxidation taking place under different circumstances. The role of carbon during oxidation in a CO/CO2 atmosphere is also discussed as is the way in which a given alloy can show either chemical or mechanical passivation failure in different environments.
No preview · Article · Aug 2011 · Journal of Microscopy
[Show abstract][Hide abstract] ABSTRACT: We describe the formation of RuO2 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 RuO2 islands. No significant changes in composition or morphology are observed following annealing in N-2 for 4 h at either 500 or 700 degrees C. Higher temperature annealing in N-2 (820 degrees C, 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 RuO2 to Ru metal is, obtained after annealing in forming gas (95% N-2/5% H-2) at 420 degrees C for 5 min.
No preview · Article · Jun 2011 · Chemical Vapor Deposition
[Show abstract][Hide abstract] ABSTRACT: The atomic layer deposition of high dielectric constant oxides like HfO <sub>2</sub> on III-V substrates such as In <sub>0.53</sub> Ga <sub>0.47</sub> As leads to a poor interface, with the growth of In <sub>0.53</sub> Ga <sub>0.47</sub> As 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 deposition (ALD) growth of a thin (∼1 nm ) Al <sub>2</sub> O <sub>3</sub> layer before the ALD growth of HfO <sub>2</sub> causes a removal/reduction of the native oxides on the surface by a self-cleaning process without subsequent regrowth of the native oxides. As a result, there are significant improvements in gate leakage current densities, and significant improvements in the frequency dispersion of capacitance versus gate voltage, even when a defective In <sub>0.53</sub> Ga <sub>0.47</sub> As epitaxial layer on an InP substrate is employed. Measurements at different -
temperatures confirm that the frequency dispersion is mainly due to interface state defect responses and another weakly temperature dependent mechanism such as border traps, after accounting for the effects of nonideal In <sub>0.53</sub> Ga <sub>0.47</sub> As epitaxial layer growth defects where applicable.
Full-text · Article · Feb 2011 · Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society
[Show abstract][Hide abstract] ABSTRACT: The oxidation behaviour of austenitic and ferritic alloys containing 4% Al and rare-earth element addition of (La + Ce) has been investigated, and comparisons made to an austenitic alloy with no such addition. The alloys were all found to exhibit good oxidation resistance; although, such resistance was highest when the alloy contained rare-earth elements. The addition led to a reduction in the amount of scale spalling. The scales formed after 10 and 100 h at 1,000 °C were examined using transmission electron microscopy and found to have bi-layered microstructures. The dislocation density and an amount of distortion in the scale were found to differ, depending on the absence or presence of (La + Ce) in the metal. It was observed that the outer-to-inner layer thickness ratio changed with time and the rare-earth element addition promoted growth of the inner layer relative to the outer layer. Analysis of the scale compositions demonstrated an apparent synergistic relationship between the effects of the rare-earth element addition and the degree to which iron is incorporated within the scales. The results are discussed in relation to the relative oxidation performance of the austenitic and ferritic alloys.
No preview · Article · Feb 2011 · Oxidation of Metals
[Show abstract][Hide abstract] ABSTRACT: In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide ( NH <sub>4</sub>)<sub>2</sub> S concentrations in the passivation of n -type and p -type In <sub>0.53</sub> Ga <sub>0.47</sub> As . Samples were degreased and immersed in aqueous ( NH <sub>4</sub>)<sub>2</sub> S solutions of concentrations 22%, 10%, 5%, or 1% for 20 min at 295 K, immediately prior to atomic layer deposition of Al <sub>2</sub> O <sub>3</sub> . Multi-frequency capacitance-voltage (C-V) results on capacitor structures indicate that the lowest frequency dispersion over the bias range examined occurs for n -type and p -type devices treated with the 10 % ( NH <sub>4</sub>)<sub>2</sub> S solution. The deleterious effect on device behavior of increased ambient exposure time after removal from 10 % ( NH <sub>4</sub>)<sub>2</sub> S solution is also presented. Estimations of the interface state defect density ( D <sub> it </sub>) for the optimum 10 % ( NH <sub>4</sub>)<sub>2</sub> S passivated In <sub>0.53</sub> Ga <sub>0.47</sub> As devices extracted using an approximation to the conductance method, and also extracted using the temperature-modified high-low frequency C-V method, indicate that the same defect is present over n -type and p -type devices having an integrated D <sub> it </sub> of ∼2.5×10<sup>12</-
sup> cm <sup>-2</sup> (±1×10<sup>12</sup> cm <sup>-2</sup>) with the peak density positioned in the middle of the In <sub>0.53</sub> Ga <sub>0.47</sub> As band gap at approximately 0.37 eV (±0.03 eV) from the valence band edge. Both methods used for extracting D <sub> it </sub> show very good agreement, providing evidence to support that the conductance method can be applied to devices incorporating high- k oxides on In <sub>0.53</sub> Ga <sub>0.47</sub> As .
Full-text · Article · Feb 2011 · Journal of Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Energy barriers at interfaces of (100)InP with atomic-layer deposited Al2O3 are determined using internal photoemission of electrons. The barrier height between the top of the InP valence band and bottom of the alumina conduction band is found to be 4.05±0.10 eV corresponding to a conduction band offset of 2.7 eV. An interlayer associated with the oxidation of InP may result in a lower barrier for electron injection potentially leading to charge instability of the insulating stack. A wide-gap P-rich interlayer has a potential to reduce this degrading effect as compared to In-rich oxides.
[Show abstract][Hide abstract] ABSTRACT: 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 Al <sub>2</sub> O <sub>3</sub> . A thin (∼1 nm ) Al <sub>2</sub> O <sub>3</sub> interface control layer is deposited on In <sub>0.53</sub> Ga <sub>0.47</sub> As prior to HfO <sub>2</sub> growth, providing the benefit of self-cleaning and improving the interface quality by reducing interface state defect densities by ∼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 In <sub>0.53</sub> Ga <sub>0.47</sub> As native oxides.
[Show abstract][Hide abstract] ABSTRACT: The feasibility of Aerosol Assisted Chemical Vapour Deposition (AA-CVD) has been investigated for the growth of zinc oxide (ZnO) films containing preformed metal nanoparticles. The deposition parameters were first established for ZnO thin films, by varying the heating configuration, substrate temperature and deposition time. Films were characterised using Scanning Electron Microscopy and X-Ray Diffraction. As-deposited films, grown at 250 degrees C, were mostly amorphous and transformed to highly crystalline Wurtzite ZnO at higher substrate temperatures (400-450 degrees C). A change in the preferential orientation of the films was observed upon changing (i), the substrate temperature or (ii), the heating configuration. Following this, the applicability of the AA-CVD process for the incorporation of preformed nanoparticles (platinum and gold) in ZnO thin films was investigated. It was found that surface agglomeration occurred, such that the ZnO films were capped with an inhomogeneous coverage of the metal. These layers were characterised using Transmission Electron Microscopy and Electron Diffraction. A possible mechanism for the formation of these metal surface clusters is presented. (C) 2010 Elsevier B.V. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Photonic crystals made from noble metals such as silver are an interesting class of material for many applications such as chemical sensing, solar cells or photonics. Their fabrication suffers from a lack of reproducibility, and complicated and aggressive processes. In this paper we show a simple and reproducible method based on the black and white photography process, to get a self standing 3D silver photonic crystal. Their characterization by SEM and TEM allowed us to interpret the process, and optical analysis made in reflection and transmission were used to find out eventual coupling between surface plasmon polaritons and the photonics properties of the structure itself.
Full-text · Article · Aug 2010 · Journal of Materials Chemistry
[Show abstract][Hide abstract] ABSTRACT: In this paper we present our development of a SF6/Cl2-based plasma etch recipe for a LAM Research 4720 etch chamber. Our tungsten plasma etch recipe is used to pattern nanoscale resistor features integrated within a novel IR sensor process. We characterised the nanoscale etch in terms of five primary process parameters using a 16-run V fractional factorial experiment, to provide accurate estimates of all main effects and two-factor interactions. The experimental results determined the target levels for the etch process parameters. Our optimised nanoscale tungsten etch module was then integrated within a CMOS/MEMs-compatible nanobolometer infrared (IR) sensor fabrication flow. Our use of tungsten improves the reliability of the sensor pixels at elevated stress current levels, when compared with equivalent Ti-based pixel structures, and demonstrates the potential of tungsten as a CMOS-compatible nanobolometer material.
No preview · Article · May 2010 · Microelectronic Engineering
[Show abstract][Hide abstract] ABSTRACT: Off-axis electron holography has been used to characterize a linear array of transistors, which was prepared for examination in cross-sectional geometry in the transmission electron microscope using focused ion beam milling. In reconstructed phase images, regions of silicon oxide that are located between metal contacts show unexpected elliptical phase contours centered several hundreds of nm from the specimen edge. The experimental images are compared with simulations performed using three-dimensional calculations of the electrostatic potential inside and outside the specimen, which take into account the mean inner potential of the specimen and the perturbed vacuum reference wave. The simulations suggest that the oxide layers contain a uniform volume density of positive charge and that the elliptical contours result from the combined effect of the electrostatic potential in the specimen and the external electrostatic fringing field.
No preview · Article · Feb 2010 · Journal of Physics Conference Series
[Show abstract][Hide abstract] ABSTRACT: MgO has been suggested as a possible high- k dielectric for future complementary metal-oxide semiconductor processes. In this work, the time dependent dielectric breakdown (TDDB) characteristics of 20 nm MgO films are discussed. Stress induced leakage current measurements indicate that the low measured Weibull slopes of the TDDB distributions for both n -type and p -type devices cannot be attributed to a lower trap generation rate than for SiO <sub>2</sub> . This suggests that much fewer defects are required to trigger breakdown in MgO under voltage stress than is the case for SiO <sub>2</sub> or other metal-oxide dielectrics. This in turn explains the progressive nature of the breakdown in these films which is observed both in this work and elsewhere. The reason fewer defects are required is attributed to the morphology of the films.
Full-text · Article · Feb 2010 · Journal of Applied Physics