L. Faraone

University of Auckland, Окленд, Auckland, New Zealand

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Publications (341)364.29 Total impact

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    ABSTRACT: Photostriction-based all-optical actuation of silicon micro-cantilevers has been investigated through experimental characterization of structures fabricated on silicon-on-insulator substrates, and through numerical modeling and analysis of their semiconductor device and micromechanical characteristics. Since the pressure coefficient of the bandgap is negative in Si, photostriction-induced photoactuation in Si-based cantilevers was evident as upward mechanical defections (away from the substrate) in response to pulsed laser illumination on the cantilevers’ top surface; which is in contrast to the downward deflections typical of photothermal effects. For the numerical modeling of photostriction induced effects, carrier lifetime and excess-carrier concentrations were determined from transient photoconductance measurements. The experimentally determined parameters were then employed to simulate carrier-density profiles across the modeled structure. The modeled cantilever deflections were found to be in excellent agreement with experimentally determined deflections. It is also shown that 100-um-long Si cantilevers were deflected by up to 10 nm, and generated a force of 0.14 nN, when optically actuated by a 405-nm laser power density of 400 W/cm2.
    Journal of Microelectromechanical Systems 06/2014; · 2.13 Impact Factor
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    ABSTRACT: In this work, GaSb is proposed as a new alternative substrate for the growth of HgCdTe via molecular beam epitaxy (MBE). Due to the smaller mismatch in both lattice constant and coefficient of thermal expansion between GaSb and HgCdTe, GaSb presents a better alternative substrate for the epitaxial growth of HgCdTe, in comparison to alternative substrates such as Si, Ge, and GaAs. In our recent efforts, a CdTe buffer layer technology has been developed on GaSb substrates via MBE. By optimizing the growth conditions (mainly growth temperature and VI/II flux ratio), CdTe buffer layers have been grown on GaSb substrates with material quality comparable to, and slightly better than, CdTe buffer layers grown on GaAs substrates, which is one of the state-of-the-art alternative substrates used in growing HgCdTe for the fabrication of mid-wave infrared detectors. The results presented in this paper indicate the great potential of GaSb to become the next generation alternative substrate for HgCdTe infrared detectors, demonstrating MBE-grown CdTe buffer layers with rocking curve (double crystal x-ray diffraction) full width at half maximum of ̃60 arcsec and etch pit density of ̃106 cm-2.
    01/2014;
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    ABSTRACT: In this paper, we present the results of a numerical study on the influence of discrete dopant atom distribution and crystal orientation on the electrical characteristics of $p$-channel silicon nanowire-based transistors using 3-D quantum simulations. The valence band was modeled employing a three-band $k.p$ Hamiltonian with optimized Lüttinger parameters, while the device characteristics were obtained by modeling hole carrier transport through a self-consistent solution of Poisson's equation and the nonequilibrium Green's function formalism. Simulation of various discrete impurity configurations show that impurities located near the center of the channel region have the greatest impact on threshold voltage. It is shown that the effect of donor-like impurities on device threshold voltage is virtually independent of the nanowire's crystallographic orientation, whereas discrete acceptor-like impurities induce smaller threshold voltage shifts in nanowire transistors oriented along the [110] and [111] directions; thus suggesting that the devices oriented along these directions would be relatively less sensitive to the effects of unintentional impurities on threshold voltage.
    IEEE Transactions on Electron Devices 01/2014; 61(2):386-393. · 2.06 Impact Factor
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    ABSTRACT: Three-dimensional (3D) topological insulators (TI) are a new state of quantum matter in which surface states reside in the bulk insulating energy bandgap and are protected by time-reversal symmetry. It is possible to create an energy bandgap as a consequence of the interaction between the conduction band and valence band surface states from the opposite surfaces of a TI thin film, and the width of the bandgap can be controlled by the thin film thickness. The formation of an energy bandgap raises the possibility of thin-film TI-based metal-oxide-semiconductor field-effect-transistors (MOSFETs). In this paper, we explore the performance of MOSFETs based on thin film 3D-TI structures by employing quantum ballistic transport simulations using the effective continuous Hamiltonian with fitting parameters extracted from ab-initio calculations. We demonstrate that thin film transistors based on a 3D-TI structure provide similar electrical characteristics compared to a Si-MOSFET for gate lengths down to 10 nm. Thus, such a device can be a potential candidate to replace Si-based MOSFETs in the sub-10 nm regime.
    Journal of Applied Physics 01/2014; 116(8):084508-084508-8. · 2.21 Impact Factor
  • S. Safa, A. Asgari, L. Faraone
    Journal of Applied Physics 01/2014; 115(14):146102-146102-2. · 2.21 Impact Factor
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    ABSTRACT: A miniature Fabry-Perot etalon was designed and fabricated to provide spectral filtering capability at the resonance wavelength of 10 μm. A high transmission peak of 85% and a relatively broad bandwidth of 500 nm are expected based on optical modeling. Optimal deposition conditions for process durable thin film materials were developed and optical constants of these materials were characterized. Fabrication of devices was accomplished using standard surface micromachining technique. Released mirrors exhibited a deflection of 400 nm over a length of 150 μm.
    11/2013;
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    ABSTRACT: An electron transfer quantum well infrared photodetector (QWIP) consisting of repeating units of two coupled quantum wells (QWs) is capable of exhibiting a two color voltage dependent spectral response. However, significant electron transfer between the coupled QWs is required for spectral tuning, which may require the application of relatively high electric fields. Also, the band structure of coupled quantum wells is more complicated in comparison to a regular quantum well and, therefore, it is not always obvious if an electron transfer QWIP can be designed such that it meets specific performance characteristics. This paper presents a feasibility study of the electron transfer QWIP and its suitability for spectral tuning. Self consistent calculations have been performed of the bandstructure and the electric field that results from electron population within the quantum wells, from which the optical characteristics have been obtained. The band structure, spectral response, and the resonant final state energy locations have been compared with standard QWIPs. It is shown that spectral tuning in the long-wave infrared band can be achieved over a wide wavelength range of several microns while maintaining a relatively narrow spectral response FWHM. However, the total absorption strength is more limited in comparison to a standard QWIP, since the higher QW doping densities require much higher electric fields for electron transfer.
    Journal of Applied Physics 11/2013; 114:194501. · 2.21 Impact Factor
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    ABSTRACT: Spin-on dopants offer an expedient, straight forward, and low cost method for doping semiconductors. These sol-gel dopant films contain sufficient impurity content to obtain surface concentrations well above the solubility limit of most semiconductors (e.g., Si, Ge). While much has been published about spin-on dopants for degenerate doping of Si, there is to the authors' knowledge no report in the literature of such films being used to achieve degenerate p-type doping of Ge, as there are a number of technical challenges associated with this technique. In this work, we present a novel technique for degenerate p-type doping of Ge using Ga spin-on dopant films in a regular horizontal tube furnace. This technique gives both excellent uniformity, higher doping concentrations and better potential for ultra-shallow junctions than diffusion from solid sources, is much preferred to rapid melt/alloyed junctions (especially for optoelectronic applications), and is readily applicable to rapid thermal processing. In this preliminary investigation, we report doping concentrations exceeding 1020cm-3 which are shown to be fully electrically activated. We report on the use of a traditional "pre-dep"/"drive-in" approach, which could be used to give shallow dopant profiles, or tailored dopant concentrations, for a wide variety of electronic and optoelectronic applications, and to form back surface fields in photovoltaic and thermo-photovoltaic devices. Values of 3.4 ± 0.2 eV and 3.2 ± 0.4 eV are extracted for the activation enthalpies of the diffusion processes into p-type 1 0 0 and n-type 2 1 1 Ge substrates, respectively, which are shown to be in good agreement with previously published data [1,2]. We conclude that Ga is a more suitable dopant for reliable, low-cost, degenerate p-type doping of Ge, rather than B (also investigated in this work), which is known to be problematic.
    Solid-State Electronics 11/2013; 89:146. · 1.48 Impact Factor
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    ABSTRACT: We report the first planar waveguides made from mercury-cadmium-telluride (MCT) - a material to date exclusively used for mid-infrared (MIR) detector elements - serving as on-chip MIR evanescent field transducer in combination with tunable quantum cascade lasers (tQCLs) emitting in the spectral regime of 5.78-6.35 µm. This novel MIR sensing approach utilizes structured MCT chips fabricated via molecular beam epitaxy (MBE) as waveguide enabling sensing via evanescent field absorption spectroscopy, as demonstrated by the detection of 1 nL of acetone. Complementary finite difference time domain (FDTD) simulations fit well with the experimentally obtained data and predict an improvement of the limit of detection by at least 2 orders of magnitude upon implementation of thinner MCT waveguides. With the first demonstration of chemical sensing using on-chip MCT waveguides, monolithically fabricated IR sensing systems directly interfacing the waveguide with the MCT detector element may be envisaged.
    Analytical Chemistry 10/2013; · 5.70 Impact Factor
  • S. Safa, A. Asgari, L. Faraone
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    ABSTRACT: In this paper, we present a study of the effects of different superlattice structural parameters on the bandgap and on both the vertical and in-plane mobility of electrons in InAs/GaSb type-II superlattices using a fully numerical finite difference method. The analysis of our results clearly indicates the significance of interface roughness scattering and, in particular, that the influence of interface roughness correlation length and height is considerable. A comparison of our calculated results with published experimental data is shown to be in good agreement.
    Journal of Applied Physics 08/2013; 114(5). · 2.21 Impact Factor
  • A. Asgari, L. Faraone
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    ABSTRACT: In this paper we present a detailed study of the effects of temperature on the two-dimensional electron mobility distribution, using a fully numerical calculation in unintentionally doped AlxGa1−xN/AlN/GaN heterostructures. The analysis of our results clearly indicates that the effect of partial sub-band occupancy is considerable, especially at higher operating temperatures when more than one sub-band is occupied. By correlating with published experimental data, our results are consistent with the observed broadening of the mobility distribution with increasing temperature, which is shown to be a direct consequence of the temperature dependence of polar optical phonons. Although other scattering mechanisms also affect broadening of the mobility distribution, the contribution from these other individual scattering mechanisms is found to be independent of temperature. In particular, a comparison of our calculated results with published experimental data is shown to be in excellent agreement across the temperature range from 100 K to 300 K. By fitting our model to experimental results at low temperatures (95 K–125 K), we are able to extract detailed information related to surface roughness scattering, which is dominant in this temperature range. In particular, the average height of interface roughness is found to be 18 A.
    Journal of Applied Physics 08/2013; 114(5). · 2.21 Impact Factor
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    ABSTRACT: We report results of a detailed study of electronic transport in n-on-p junctions formed by 150-keV boron-ion implantation in vacancy-doped p-type Hg0.769Cd0.231Te without postimplantation thermal annealing. A mobility spectrum analysis methodology in conjunction with a wet chemical etching-based surface removal approach has been employed to depth profile the transport characteristics of the samples. In the as-implanted samples, three distinct electron species were detected which are shown to be associated with (a) low-mobility electrons in the top 220-nm surface-damaged layer (E1: μ80K = 2940 cm2/Vs), (b) the B-ion implantation region in the top 500-nm region (E2: μ80K = 7490 cm2/Vs), and (c) high-mobility electrons in the n-to-p transition region at a depth of 600 nm to 700 nm (E3: μ80K = 25,640 cm2/Vs). Due to the maximum magnetic field employed (2 T), hole carriers from the underlying vacancy-doped p-type region were detected only after the removal of the top 220 nm of the profiled sample (μ80K = 126 cm2/Vs), revealing fully p-type character 800 nm below the original sample surface. A comparison of the extracted E2 electron concentration and calculated B-impurity profile suggests that the n-type region is due primarily to near-surface implantation-induced lattice damage. © 2013 TMS.
    Journal of Electronic Materials 06/2013; · 1.64 Impact Factor
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    ABSTRACT: A bound-to-continuum quantum well solar cell structure is proposed, and the band structure and absorption spectra are analyzed by the use of an eight band k·p model. The structure is based on quantum wells that only support bound states for the valence band. The absence of bound conduction band states has a number of potential advantages, including a reduction of electron trapping and, therefore, a reduction of quantum well induced photocarrier recombination due to reduced spatial overlap of the electron and hole wavefunctions.
    Applied Physics Letters 05/2013; 102(21). · 3.79 Impact Factor
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    ABSTRACT: This paper presents a macromodel for the transient simulation of fixed-fixed beams (FFBs). Based on the energy method, the proposed macromodel enables system-level simulation of FFB beams with their associated read out circuitry. It is geared towards use in network simulators such as SPICE. In contrast to previously reported works, the proposed macromodel accounts for fringing field effects and relies on a novel and more accurate beam profile. As a result the proposed macromodel exhibits a capacitance error of only 3.2% and a 50% improvement in deflection accuracy compared to prior works.
    Circuits and Systems (ICCAS), 2013 IEEE International Conference on; 01/2013
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    ABSTRACT: This paper reports on the fabrication of cantilever silicon-on-insulator (SOI) optical waveguides and presents solutions to the challenges of using a very thin 260-nm active silicon layer in the SOI structure to enable single-transverse-mode operation of the waveguide with minimal optical transmission losses. In particular, to ameliorate the anchor effect caused by the mean stress difference between the active silicon layer and buried oxide layer, a cantilever flattening process based on Ar plasma treatment is developed and presented. Vertical deflections of 0.5 $muhbox{m}$ for 70-$ muhbox{m}$-long cantilevers are mitigated to within few nanometers. Experimental investigations of cantilever mechanical resonance characteristics confirm the absence of significant detrimental side effects. Optical and mechanical modeling is extensively used to supplement experimental observations. This approach can satisfy the requirements for on-chip simultaneous readout of many integrated cantilever sensors in which the displacement or resonant frequency changes induced by analyte absorption are measured using an optical-waveguide-based division multiplexed system.$hfill$[2012-0180]
    Journal of Microelectromechanical Systems 01/2013; 22(3):569-579. · 2.13 Impact Factor
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    ABSTRACT: Vertical minority carrier electron transport parameters in p-type InAs/GaSb type-II superlattices for long wavelength infrared (LWIR) detection have been extracted from magnetic field dependent geometrical magneto-resistance. The measurements, performed at low electric fields and at magnetic field intensities up to 12 T, exhibited multiple-carrier conduction characteristics that required mobility spectrum analysis for the extraction of individual carrier mobilities and concentrations. Within the common operating temperature range for LWIR photodiodes (80 to 150 K), the conductivity was found to be dominated by three distinct carriers, attributed to majority holes (µ=280±27 cm 2 /Vs), minority electrons (µ=2,460±75 cm 2 /Vs), and parasitic sidewall inversion layer electrons (µ=930±55 cm 2 /Vs). A miniband energy gap of 140±15 meV for the 14/7-monolayer InAs/GaSb superlattice was estimated from the thermal activation of the minority carrier electron density. Among the infrared (IR) detector technologies avail-able today, photon detectors are pre-eminent in terms of performance, with HgCdTe-based technology still domi-nating the high performance arena. InAs/GaSb type-II superlattices (T2SL) have been identified as suitable ma-terial for IR detectors 1 , and recent progress has enabled the demonstration of detectors with performance levels approaching those of HgCdTe-based devices, with the-oretical calculations predicting that InAs/GaSb T2SL-based IR detectors can significantly outperform present state-of-the-art HgCdTe devices 2,3 In spite of this significant progress there are still funda-mental properties of the InAs/GaSb T2SL material sys-tem that are not fully understood. For example, Auger recombination is the dominant source of noise in high performance HgCdTe photodiodes and it has been re-ported that the T2SL should have a lower Auger recom-bination rate than HgCdTe due to the absence of higher lying hole states to scatter into 4,5 . However, the minor-ity carrier lifetime in InAs/GaSb T2SL has been found to be limited to 50 ns due to Shockley-Read-Hall (SRH) processes 6 . The origin of the generation-recombination (GR) centre(s) associated with such SRH processes is not yet well understood. Similarly, the background car-rier concentration in the superlattices has been estimated by capacitance-voltage measurements 7 . However, since the system is not a bulk semiconductor, the actual num-ber of carriers contributing to carrier transport cannot be explicitly obtained. Moreover, there is currently no experimentally measured transport parameters for car-riers travelling in the direction perpendicular to the su-perlattice plane, which is the direction in which photo-generated carriers are collected in photovoltaic detectors. It is notable, nevertheless, that Burkle et al . estimated a minority electron mobility of 1,100∼1,300 cm 2 /Vs at 120K from the magnetic field dependence of the zero-bias dynamic resistance-area product (R o A) of long-wave in-frared photodiodes with a superlattice period of 8
    Applied Physics Letters 12/2012; 101(25):253515. · 3.79 Impact Factor
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    ABSTRACT: Rare earth cerium substituted europium iron garnets (CeEu) 3 (FeGa) 5 O 12 (Ce:EIG) as well as the elemental oxides were deposited on fused quartz sub-strates using Biased Target Deposition (BTD). The Ce:EIG films are prepared at low temperature (80-120ºC) by sputtering four metallic targets simultaneously using a low energy ion beam. This method pro-vides control over the material composi-tion in a predictable way by controlling the bias duty cycle on individual targets. 1 Introduction: Rare earth substituted iron garnets are well known for their magneto-optical properties that make them well suited for the applications such as optical isolators, high speed temporal modulators, lightwave polarisation con-trollers etc. The cerium substituted euro-pium iron garnets (Ce:EIG) have potential applications in the visible spectrum of be-tween 400 and 700nm and in the infrared spectrum around 1550nm for optical communications.
    Conference on Optoelectronic and Microelectronic Materials and Devices, Melbourne; 12/2012
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    ABSTRACT: Rare earth cerium substituted europium iron garnets (CeEu) 3 (FeGa) 5 O 12 (Ce:EIG) as well as the elemental oxides were deposited on fused quartz sub-strates using Biased Target Deposition (BTD). The Ce:EIG films are prepared at low temperature (80-120ºC) by sputtering four metallic targets simultaneously using a low energy ion beam. This method pro-vides control over the material composi-tion in a predictable way by controlling the bias duty cycle on individual targets.
    COMMAD; 12/2012

Publication Stats

1k Citations
364.29 Total Impact Points

Institutions

  • 2012
    • University of Auckland
      Окленд, Auckland, New Zealand
  • 1900–2012
    • University of Western Australia
      • School of Electrical, Electronic and Computer Engineering
      Perth, Western Australia, Australia
  • 2010
    • University of Southampton
      Southampton, England, United Kingdom
  • 2009
    • Military University of Technology
      • Division of Applied Physics
      Warsaw, Masovian Voivodeship, Poland
  • 2008
    • Università degli studi di Parma
      • Department of Information Engineering
      Parma, Emilia-Romagna, Italy
  • 2005
    • University of Tabriz
      • Research Institute for Applied Physics and Astronomy
      Tebriz, East Azarbaijan, Iran
  • 2004
    • University of California, Santa Barbara
      • Department of Electrical and Computer Engineering
      Santa Barbara, California, United States
  • 1999
    • Vigo System S.A.
      Ożarów-Franciszków, Masovian Voivodeship, Poland
    • Korea Advanced Institute of Science and Technology
      • Department of Electrical Engineering
      Seoul, Seoul, South Korea
  • 1984
    • University of Bradford
      Bradford, England, United Kingdom
  • 1981–1982
    • Lehigh University
      Bethlehem, Pennsylvania, United States
    • University of Toronto
      • Department of Electrical and Computer Engineering
      Toronto, Ontario, Canada