J. F. Klem

Sandia National Laboratories, Albuquerque, New Mexico, United States

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Publications (227)367.78 Total impact

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    ABSTRACT: Measurements of carrier recombination rates using a time-resolved pump-probe technique are reported for mid-wave infrared InAs/InAs1−xSbx type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions, a 16 K band-gap of ≃235 ± 10 meV was achieved for all five unintentionally doped T2SLs. Carrier lifetimes were determined by fitting a rate equation model to the density dependent data. Minority carrier lifetimes as long as 10 μs were measured. On the other hand, the Auger rates for all the InAs/InAsSb T2SLs were significantly larger than those previously measured for InAs/GaSb T2SLs. The minority carrier and Auger lifetimes were observed to generally increase with increasing antimony content and decreasing layer thickness.
    Applied Physics Letters 01/2014; 105(2):022107-022107-4. · 3.79 Impact Factor
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    ABSTRACT: We present the design, realization and characterization of strong coupling between an intersubband transition and a monolithic metamaterial nanocavity in the mid-infrared spectral range. We use a ground plane in conjunction with a planar metamaterial resonator for full three-dimensional confinement of the optical mode. This reduces the mode volume by a factor of 1.9 compared to a conventional metamaterial resonator while maintaining the same Rabi frequency. The conductive ground plane is implemented using a highly doped n<sup>+</sup> layer which allows us to integrate it monolithically into the device and simplify fabrication.
    Optics Express 12/2013; 21(26):32572-81. · 3.55 Impact Factor
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    ABSTRACT: The interaction between cavity modes and optical transitions leads to new coupled light-matter states in which the energy is periodically exchanged between the matter states and the optical mode. Here we present experimental evidence of optical strong coupling between modes of individual sub-wavelength metamaterial nanocavities and engineered optical transitions in semiconductor heterostructures. We show that this behaviour is generic by extending the results from the mid-infrared (~10 μm) to the near-infrared (~1.5 μm). Using mid-infrared structures, we demonstrate that the light-matter coupling occurs at the single resonator level and with extremely small interaction volumes. We calculate a mode volume of 4.9 × 10(-4) (λ/n)(3) from which we infer that only ~2,400 electrons per resonator participate in this energy exchange process.
    Nature Communications 11/2013; 4:2882. · 10.02 Impact Factor
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    ABSTRACT: Minority carrier lifetimes in doped and undoped mid-wave infrared InAs/InAsSb type-II superlattices (T2SLs) and InAsSb alloys were measured from 77-300 K. The temperature-dependent lifetimes were analyzed using Shockley-Read-Hall (SRH), ra- diative, and Auger recombination, allowing the contributions of the various recom- bination mechanisms to be distinguished and the dominant mechanisms identified. For the T2SLs, SRH recombination is the dominant mechanism below 200 K and Auger recombination above 200 K. The alloy lifetimes are limited by radiative and Auger recombination through the entire temperature range, with SRH not making a significant contribution. The data allowed the extraction of SRH defect level energies.
    Applied Physics Letters 07/2013; 103(5):052106. · 3.79 Impact Factor
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    ABSTRACT: We present ultra-strong light-matter interaction of a metamaterial mode and an intersubband transition for normal incidence radiation in the mid-infrared spectral region. The anti-crossed lines show a splitting of 15% of the central frequency.
    CLEO: QELS_Fundamental Science; 06/2013
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    ABSTRACT: We present here our recent quantum transport results around the charge neutrality point (CNP) in a type-II InAs/GaSb field-effect transistor. At zero magnetic field, a conductance minimum close to 4e^2/h develops at the CNP and it follows semi-logarithmic temperature dependence. In quantized magnetic (B) fields and at low temperatures, well developed integer quantum Hall states are observed in the electron as well as hole regimes. Quantum transport shows noisy-like behavior around the CNP at extremely high B fields. Surprisingly, when the diagonal conductivity \sigma_{xx} is plotted against the Hall conductivity \sigma_{xy}, a circular conductivity law is discovered, suggesting a chaotic quantum transport behavior.
    Applied Physics Letters 04/2012; 102(3). · 3.79 Impact Factor
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    ABSTRACT: Measurements of carrier recombination rates using time-resolved differential transmission are reported for an unintentionally doped mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice. Measurements at 77 K yield minority carrier lifetimes of 3 μs and 9 μs for the InAsSb alloy and InAs/InAsSb superlattice, respectively. The un-optimized InAsSb-based materials also exhibit long lifetimes (>850 ns) at temperatures up to 250 K, indicating the potential use for these materials as mid-wave infrared photodetectors with improved performance over current type-II superlattice photodetectors at both cryogenic and near-ambient operating temperatures.
    Applied Physics Letters 01/2012; 101:092109. · 3.79 Impact Factor
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    ABSTRACT: A series of type-II GaAs/AlAs superlattices epitaxially grown with different interrupts have been investigated using the techniques of grazing incidence X-ray scattering and diffraction. The interrupts are specifically designed to alter the interfacial roughness in the superlattices for the present study. Various structural parameters including the layer thickness, interfacial roughness, and intra-layer correlation lengths of fluctuations in the quantum-well widths have been determined. These results are compared with measurements made on the same set of samples using photoluminescence and optical imaging techniques.
    Modern Physics Letters B 11/2011; 11(24). · 0.48 Impact Factor
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    ABSTRACT: We have fabricated mid-wave infrared photodetectors containing InAsSb absorber regions and AlAsSb barriers in n-barrier-n (nBn) and n-barrier-p (nBp) configurations, and characterized them by current-voltage, photocurrent, and capacitance-voltage measurements in the 100-200 K temperature range. Efficient collection of photocurrent in the nBn structure requires application of a small reverse bias resulting in a minimum dark current, while the nBp devices have high responsivity at zero bias. When biasing both types of devices for equal dark currents, the nBn structure exhibits a differential resistance significantly higher than the nBp, although the nBp device may be biased for arbitrarily low dark current at the expense of much lower dynamic resistance. Capacitance-voltage measurements allow determination of the electron concentration in the unintentionally-doped absorber material, and demonstrate the existence of an electron accumulation layer at the absorber/barrier interface in the nBn device. Numerical simulations of idealized nBn devices demonstrate that photocurrent collection is possible under conditions of minimal absorber region depletion, thereby strongly suppressing depletion region Shockley-Read-Hall generation.
    Proc SPIE 01/2010;
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    ABSTRACT: We demonstrate InGaAs photodiodes with an epitaxial heterostructure that allows simple mesa isolation of individual devices with low dark current and high responsivity. An undoped InAlAs barrier and passivation layer enables isolation of detectors without exposing the InGaAs active region, while simultaneously reducing electron diffusion current. Photodetectors with mesa sizes as small as 25×25 μm2 exhibit dark current densities of 10 nA/cm2 at 295 K and responsivities of 0.62 A/W at 1550 nm.
    Applied Physics Letters 07/2009; 95(3):031112-031112-3. · 3.79 Impact Factor
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    ABSTRACT: The experimental characterization of single barrier heterostructure thermionic cooling devices at cryogenic temperatures is reported. The device studied was a cylindrical InGaAs microrefrigerator, in which the active layer was a 1μm thick In0.527Al0.218Ga0.255As heterostructure barrier with n-type doping concentration of 6.68×1016cm−3 and an In0.53Ga0.47As emitter/collector of 5×1018cm−3 n-doping. A full field thermoreflectance imaging technique was used to measure the distribution of temperature change on the device’s top surface when different current excitation values were applied. By reversing the current direction, we studied the device’s behavior in both cooling and heating regimes. At an ambient temperature of 100K, a maximum cooling of 0.6K was measured. This value was approximately one-third of the measured maximum cooling value at room temperature (1.8K). The paper describes the device’s structure and the first reported thermal imaging at cryogenic temperatures using the thermoreflectance technique.
    Journal of Electronic Materials 01/2009; 38(7):1309-1314. · 1.64 Impact Factor
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    ABSTRACT: We demonstrate a compact, all-optical XOR gate at 1550 nm by integrating three symmetric self-electrooptic effect devices (S-SEEDs) with micro-optics. Each S-SEED operates as a NAND or NOR gate and can switch faster than 10 ps.
    Photonics in Switching, 2008. PS 2008. International Conference on; 09/2008
  • 01/2008;
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    ABSTRACT: We present experimental results on the development of bottom-emitting GaInNAs vertical-cavity surface-emitting lasers (VCSELs) operating at wavelengths near 1300 nm. This development effort is based on the modification of oxide-apertured top-emitting structures to allow emission through the GaAs substrate. Similar device performance was seen in both the top- and bottom-emitting structures. Single-mode output powers (adjusted for substrate absorption) of ∼0.75 mW, with threshold currents of 1.3 mA, were achieved with ∼3.5-μm aperture diameters. Larger multimode devices exhibited a maximum adjusted output power of 2.2 mW. To the best of our knowledge, these are the first bottom-emitting flip-chip compatible 1300-nm VCSELs fabricated with GaInNAs-GaAs active regions.
    IEEE Photonics Technology Letters 05/2004; · 2.04 Impact Factor
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    ABSTRACT: The molecular beam epitaxial growth of GaPSb and Ga-rich AlGaPSb nearly lattice matched to InP has been investigated. The effect of growth temperature, P flux, Ga flux, and Sb flux on the alloy P/Sb ratio was examined. The 300 K band gap of lattice-matched GaPSb was estimated to be 0.84 eV based on photoluminescence measurements, and the shift of band gap energy with Al content in AlGaPSb alloys with Al fractions of 0.03–0.04 was investigated. A conduction band offset of approximately 0.15 eV in a type-II configuration was estimated between lattice-matched Al0.04Ga0.96P0.35Sb0.65 and InP based on photoluminescence characterization of multiple quantum well structures. AlGaPSb/InP distributed Bragg reflectors (DBRs) with a stopband centered on 1550 nm were grown with excellent lattice matching and good surface morphology. A refractive index difference of 0.41 between these materials was estimated based on a fit to the DBR reflectance spectrum. © 2004 American Vacuum Society.
    Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2004; 22(3). · 1.36 Impact Factor
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    ABSTRACT: We report a measurement of the variation of the diamagnetic shift of a heavy-hole exciton in a single coherently strained GaAs0.685Sb0.3N0.015/GaAs quantum well as a function of magnetic field up to 32 T at 1.3 K using photoluminescence spectroscopy. The excitons are known to be localized in this alloy system. This localization is simulated by assuming that the hole is completely immobilized, i.e., its mass is infinite. Using this model we have calculated the variation of the diamagnetic shift with magnetic field in this quantum well structure following a variational approach. We find that the observed variation of the diamagnetic shift with magnetic field agrees quite well with that calculated when the mass of the conduction electron in the well is assumed to be 0.09 m0, about 50% larger than in GaAs0.7Sb0.3, an increase similar to that found in GaAsN for the same nitrogen composition. © 2003 American Institute of Physics.
    Applied Physics Letters 12/2003; 83(26):5425-5427. · 3.79 Impact Factor
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    ABSTRACT: We have measured the diamagnetic shift of a heavy-hole exciton in a single 60 Å wide GaAs0.7Sb0.3/GaAs quantum well as a function of magnetic field up to 32 T at 1.3 K using photoluminescence spectroscopy. The sample was grown on (001)-oriented GaAs substrate using solid-source molecular beam epitaxy. We have calculated the variation of the diamagnetic shift as a function of magnetic field using a variational approach and a free exciton model. We assumed a weak type-I conduction-band lineup in our calculations. We found that the values thus obtained are more than twice as large as the observed values. A similar calculation assuming a complete localization of the heavy hole leads to the values of the diamagnetic shift which agree very well with the experimental data. Our study suggests that the excitons are strongly localized in GaAs0.7Sb0.3/GaAs quantum well structures at low temperatures, and that this heterostructure has a weak type-I conduction-band lineup. © 2003 American Institute of Physics.
    Applied Physics Letters 09/2003; 83(13):2614-2616. · 3.79 Impact Factor
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    ABSTRACT: We present low-temperature (T=4K) photoluminescence (PL) studies of the effects of adding 1 to 2single GaAsSb quantum wells (QW) on GaAs (GaSb content 30grown by both MBE and MOCVD techniques. The observed band gap energy for the as-grown GaAsSb/GaAs QWs was 1.021eV. The full-width-half-maximum linewidths were about 18meV. The addition of nitrogen reduced the band gap energies from 1eV to 0.75eV. A rapid thermal anneal increased both the PL intensities by about 10x and the band gap energies by 50-100meV, and decreased the PL linewidths from 34 to 22meV. Annealing non-nitrogen containing quantum well samples did not affect PL line intensity, position, or width, indicating that the observed variations for the N-containing samples are probably not a result of As, Sb, or Ga loss and/or diffusion. The results of a first-principles band structure calculation for the GaAsSbN system will be discussed. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
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    ABSTRACT: Distributed Bragg reflectors (DBRs) not only serve as high-reflectance mirrors to define the laser cavity of a vertical-cavity surface-emitting laser (VCSEL), but they also must conduct electricity, confine currents, and provide a single-crystal template for the gain region of the laser. Basic optical and electrical properties of DBRs are presented in this article. Three examples of DBR structures used in VCSEL applications from the ultraviolet to the infrared are given to illustrate the complexity and range of materials science issues that are encountered in DBR growth. Fabrication issues are also discussed.
    MRS Bulletin. 07/2002; 27(07).
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    ABSTRACT: Deep-level transient spectroscopy (DLTS) studies on both p-type unintentionally doped and n-type (Si-doped), 1.05 eV band gap InGaAsN grown by molecular-beam epitaxy are reported. Two majority-carrier hole traps were observed in p-type material, H3′ (0.38 eV) and H4′ (0.51 eV), and no evidence was found for the presence of minority-carrier electron traps. In n-type material, we observed a shallow distribution of electron levels, E1′, as well as a deep electron trap E4′ (0.56 eV) and a deep hole trap H5′ (0.71 eV). All DLTS peaks observed were broad and are thus consistent with continuous defect distributions and/or groups of closely spaced discrete energy levels in the band gap. Comparison of the spectra to previously reported spectra of metalorganic chemical vapor deposition-grown InGaAsN of the same composition revealed some similarities and some differences, suggesting that some of the observed deep levels are due to intrinsic physical sources, whereas others are specific to the growth technique used. © 2002 American Institute of Physics.
    Applied Physics Letters 06/2002; 80(25):4777-4779. · 3.79 Impact Factor

Publication Stats

1k Citations
367.78 Total Impact Points


  • 1990–2013
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States
  • 1998
    • Oklahoma State University - Stillwater
      • Department of Physics
      Stillwater, Oklahoma, United States
  • 1991–1996
    • University of New Mexico
      • Center for High Technology Materials
      Albuquerque, NM, United States
  • 1995
    • University of California, Berkeley
      • Department of Materials Science and Engineering
      Berkeley, MO, United States
  • 1993
    • University of Cambridge
      Cambridge, England, United Kingdom
    • Lawrence Berkeley National Laboratory
      • Materials Sciences Division
      Berkeley, CA, United States
  • 1992
    • Princeton University
      • Department of Electrical Engineering
      Princeton, NJ, United States
    • The University of Arizona
      • Department of Electrical and Computer Engineering
      Tucson, Arizona, United States