Joshua M. O. Zide

University of Delaware, Delaware, United States

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Publications (94)224.14 Total impact

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    ABSTRACT: Erbium arsenide (ErAs) is a semi-metallic material that self-assembles into nanoparticles when grown in GaAs via molecular beam epitaxy. We use steady-state and time-resolved photoluminescence to examine the mechanism of carrier transfer between indium arsenide (InAs) quantum dots and ErAs nanoparticles in a GaAs host. We probe the electronic structure of the ErAs metal nanoparticles (MNPs) and the optoelectronic properties of the nanocomposite and show that the carrier transfer rates are independent of pump intensity. This result suggests that the ErAs MNPs have a continuous density of states and effectively act as traps. The absence of a temperature dependence tells us that carrier transfer from the InAs quantum dots to ErAs MNPs is not phonon assisted. We show that the measured photoluminescence decay rates are consistent with a carrier tunneling model.
    Applied Physics Letters 09/2014; 105(10):103108. · 3.52 Impact Factor
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    ABSTRACT: Self-assembled core–shell structured rare-earth nanoparticles (TbErAs) are observed in a III–V semiconductor host matrix (In0.53Ga0.47As) nominally lattice-matched to InP, grown via molecular beam epitaxy. Atom probe tomography demonstrates that the TbErAs nanoparticles have a core–shell structure, as seen both in the tomographic atom-by-atom reconstruction and concentration profiles. A simple thermodynamic model is created to determine when it is energetically favorable to have core–shell structures; the results strongly agree with the observations.
    Small 08/2014; · 7.51 Impact Factor
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    Physical Review B. 01/2014; 89(4):045418.
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    ABSTRACT: Rare-earth materials epitaxially codeposited with III-V semiconductors form small, spherical rare-earth-monopnictide nanoparticles embedded within the III-V host. The small size of these particles (approximately 1.5 nm diameter) suggests that interesting electronic properties might emerge as a result of both confinement and surface states. However, ErAs nanoparticles do not exhibit any signs of quantum confinement or an emergent band gap, and these experimental observations are understood theoretically. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of TbAs nanoparticles embedded in a GaAs host, which were expected to be similar to ErAs. We study the dynamics of carrier relaxation into the TbAs states, which essentially act as traps, using optical-pump terahertz-probe transient absorption spectroscopy. By analyzing how the carrier relaxation rates depend on pump fluence and sample temperature, we conclude that the TbAs states are saturable. Saturable traps suggest the existence of a band gap for TbAs nanoparticles, in sharp contrast with the results for ErAs.
    Physical Review B 12/2013; 89(4). · 3.66 Impact Factor
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    ABSTRACT: We demonstrate molecular beam epitaxy (MBE) grown degenerately doped InGaBiAs:Si as a new transparent contact material usable from the near-infrared (near-IR) to the mid-infrared (mid-IR). This material system can exhibit high transparency over large portions of the 1.3-12.5 μm wavelength range, with the exact transparency windows determined by the material carrier concentration. As a comparison, the transmittance of the more conventional IR contact material, Indium Tin Oxide (ITO), drops rapidly for wavelengths longer than 1.5 μm. The conductivity of InGaBiAs:Si is also much higher than ITO due to its high doping concentration and good mobility. Our transmission spectra are modeled using a transfer matrix formalism, and the resulting modeled IR transmission spectra closely match our experimental results with proper choice of two fitting parameters, the material plasma frequency and the scattering rate.
    Optical Materials Express 08/2013; 3(8). · 2.92 Impact Factor
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    ABSTRACT: This paper presents a model to predict the power generation of a thermoelectric generator in a temporally-varying temperature environment. The model employs a thermoelectric plate sandwiched between two different heat exchangers to convert a temporal temperature gradient in the environment to a spatial temperature gradient within the device suitable for thermoelectric power generation. The two heat exchangers are designed such that their temperatures respond to a change in the environment's temperature at different rates which sets up a temperature differential across the thermoelectric and results in power generation. In this model, radiative and convective heat transfer between the device and its surroundings, and heat flow between the two heat exchangers across the thermoelectric plate are considered. The model is simulated for power generation in Death Valley, CA during the summer using the diurnal variation of air temperature and radiative exchange with the sun and night sky as heat sources and sinks. The optimization of power generation via scaling the device size is discussed. Additional applications of this device are considered.
    Applied Thermal Engineering 07/2013; 56(s 1–2):152–158. · 2.62 Impact Factor
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    ABSTRACT: The cross-plane thermoelectric transport properties of La0.67Sr0.33MnO3 (LSMO)/LaMnO3 (LMO) oxide metal/semiconductor superlattices were investigated. The LSMO and LMO thin-film depositions were performed using pulsed laser deposition to achieve low resistivity constituent materials for LSMO/LMO superlattice heterostructures on (100)-strontium titanate substrates. X-ray diffraction and high-resolution reciprocal space mapping indicate that the superlattices are epitaxial and pseudomorphic. Cross-plane devices were fabricated by etching cylindrical pillar structures in superlattices using inductively, this coupled-plasma reactive-ion etching. The cross-plane electrical conductivity data for LSMO/LMO superlattices reveal a lowering of the effective barrier height to 223 meV as well as an increase in cross-plane conductivity by an order of magnitude compared to high resistivity superlattices. These results suggest that controlling the oxygen deficiency in the constituent materials enables modification of the effective barrier height and increases the cross-plane conductivity in oxide superlattices. The cross-plane LSMO/LMO superlattices showed a giant Seebeck coefficient of 2560 μV/K at 300 K that increases to 16 640 μV/K at 360 K. The giant increase in the Seebeck coefficient with temperature may include a collective contribution from the interplay of charge, spin current, and phonon drag. The low resistance oxide superlattices exhibited a room temperature cross-plane thermal conductivity of 0.92 W/m K, this indicating that the suppression of thermal conductivities due to the interfaces is preserved in both low and high resistivity superlattices. The high Seebeck coefficient, the order of magnitude improvement in cross-plane conductivity, and the low thermal conductivity in LSMO/LMO superlattices resulted in a two order of magnitude increase in cross-plane power factor and thermoelectric figure of merit (ZT), compared to the properties of superlattices with higher resistivity that were reported previously. The temperature dependence of the cross-plane power factor in low resistance superlattices suggests a direction for further investigations of the potential LSMO/LMO oxide superlattices for thermoelectric devices.
    Journal of Applied Physics 05/2013; 113(19). · 2.19 Impact Factor
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    ABSTRACT: Semiconductor growth rates are a critical factor for production costs and can have a significant impact on electrical properties. We use time resolved photoluminescence (TRPL) to characterize the effective lifetime of carriers in gallium arsenide - indium gallium phosphide (GaAs/InGaP) double heterostructures grown at varying rates. We measure the PL decay time as a function of laser fluence and extract an approximate trap state density by fitting this data with the Shockely-Read-Hall model of carrier recombination. Using the approximate trap densities, we then calculate minority carrier lifetimes for a range of doping conditions. The results suggest that the increased density of trap states associated with a two-fold increase in growth rate are less limiting to carrier lifetime than doping at the levels required for devices. The techniques and analysis developed here can be applied for rapid, non-destructive quantification of trap state densities in materials grown under varying conditions.
    03/2013;
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    ABSTRACT: Rare-earth-monopnictide nanoparticles epitaxially deposited within III-V semiconductors have been shown to improve the performance of devices for applications ranging from thermoelectrics to THz pulse generation. However, the electronic structure of small (approximately 1.5 nm diameter) TbAs nanoparticles remains poorly understood. We use ultrafast pump-probe spectroscopy to investigate the electronic structure of the TbAs nanoparticles. The samples studied were grown by co-deposition of Tb, Ga, and As on a GaAs substrate, resulting in TbAs nanoparticles embedded within a GaAs host. We study the dynamics of carrier relaxation into the TbAs states, which essentially act as traps, using both optical-pump terahertz-probe and optical-pump optical-probe techniques. By analyzing how the carrier relaxation rates depend on both pump fluence and sample temperature we conclude that the TbAs states are saturable, which suggests the existence of a bandgap for TbAs nanoparticles.
    03/2013;
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    ABSTRACT: Time-resolved photoluminescence is an established technique for characterizing carrier lifetimes in semiconductors, but the dependence of lifetime on excitation fluence has been only qualitatively investigated. We develop a quantitative approach for fitting fluence-dependent PL decay data to a Shockely-Read-Hall model of carrier recombination in order to extract the trap state density. We demonstrate this approach by investigating growth rate-dependent trap densities in gallium arsenide-indium gallium phosphide double heterostructures. The techniques developed here can be applied for rapid, non-destructive quantification of trap state densities in a variety of materials.
    Applied Physics Letters 01/2013; 102:182108. · 3.52 Impact Factor
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    ABSTRACT: The temperature dependence of the energy gap (E0) and the spin-orbit split (E0+ΔSO) transitions has been studied by photoreflectance for In0.53Ga0.47BixAs1-x layers with 0 < x ≤ 0.044. It has been observed that at 15 K the E0 transition shifts to red and significantly broadens with increasing Bi concentration, while the E0 + ΔSO transition is almost unaffected. The temperature-induced shifts of the E0 and E0 + ΔSO transitions in the temperature range of 15–295 K have been found to be ∼50–60 meV and ∼80–90 meV, respectively, which is very similar to the energy shift in the In0.53Ga0.47As host material over the same temperature range. Obtained results (energies and broadenings of E0 and E0+ΔSO transitions) have been analyzed using the Varshni and Bose-Einstein formulas. The Varshni and Bose-Einstein parameters have been found to be close to the parameters of conventional narrow bandgap III-V semiconductors.
    Journal of Applied Physics 12/2012; 112(11). · 2.19 Impact Factor
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    ABSTRACT: We report room temperature electronic and thermoelectric properties of Si-doped In{sub 0.52}Ga{sub 0.48}Bi{sub y}As{sub 1-y} with varying Bi concentrations. These films were grown epitaxially on a semi-insulating InP substrate by molecular beam epitaxy. We show that low Bi concentrations are optimal in improving the conductivity, Seebeck coefficient, and thermoelectric power factor, possibly due to the surfactant effects of bismuth. We observed a reduction in thermal conductivity with increasing Bi concentration, which is expected because of alloy scattering. We report a peak ZT of 0.23 at 300 K.
    Journal of Applied Physics 11/2012; 112(9). · 2.19 Impact Factor
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    ABSTRACT: Lanthanum strontium manganate (La0.67Sr0.33MnO3, i.e., LSMO)/lanthanum manganate (LaMnO3, i.e., LMO) perovskite oxide metal/semiconductor superlattices were investigated as a potential p-type thermoelectric material. Growth was performed using pulsed laser deposition to achieve epitaxial LSMO (metal)/LMO (p-type semiconductor) superlattices on (100)-strontium titanate (STO) substrates. The magnitude of the in-plane Seebeck coefficient of LSMO thin films (<20 μV/K) is consistent with metallic behavior, while LMO thin films were p-type with a room temperature Seebeck coefficient of 140 μV/K. Thermal conductivity measurements via the photo-acoustic (PA) technique showed that LSMO/LMO superlattices exhibit a room temperature cross-plane thermal conductivity (0.89 W/m·K) that is significantly lower than the thermal conductivity of individual thin films of either LSMO (1.60 W/m·K) or LMO (1.29 W/m·K). The lower thermal conductivity of LSMO/LMO superlattices may help overcome one of the major limitations of oxides as thermoelectrics. In addition to a low cross-plane thermal conductivity, a high ZT requires a high power factor (S2σ). Cross-plane electrical transport measurements were carried out on cylindrical pillars etched in LSMO/LMO superlattices via inductively coupled plasma reactive ion etching. Cross-plane electrical resistivity data for LSMO/LMO superlattices showed a magnetic phase transition temperature (TP) or metal-semiconductor transition at ∼330 K, which is ∼80 K higher than the TP observed for in-plane resistivity of LSMO, LMO, or LSMO/LMO thin films. The room temperature cross-plane resistivity (ρc) was found to be greater than the in-plane resistivity by about three orders of magnitude. The magnitude and temperature dependence of the cross-plane conductivity of LSMO/LMO superlattices suggests the presence of a barrier with the effective barrier height of ∼300 meV. Although the magnitude of the cross-plane power factor is too low for thermoelectric applications by a factor of approximately 10−4—in part because the growth conditions chosen for this study yielded relatively high resistivity films—the temperature dependence of the resistivity and the potential for tuning the power factor by engineering strain, oxygen stoichiometry, and electronic band structure suggest that these epitaxial metal/semiconductor superlattices are deserving of further investigation.
    Journal of Applied Physics 09/2012; 112(6). · 2.19 Impact Factor
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    ABSTRACT: We describe the growth conditions of InxGa1−xBiyAs1−y (lattice-mismatched and matched) on InP substrates by molecular beam epitaxy and the resulting properties. Due to their anomalously narrow bandgaps and the presence of bismuth, these materials are promising for optoelectronics and thermoelectrics. Low growth temperature and moderate As/Bi beam equivalent pressure ratios are beneficial for Bi incorporation, in good qualitative agreement with GaBiyAs1−y on GaAs. Up to 6.75% bismuth is incorporated. High resolution x-ray diffraction and reciprocal space mapping show that InxGa1−xBiyAs1−y samples exhibit good crystalline quality and zero relaxation. The band gap is reduced in agreement with theoretical predictions. Lattice-matched samples have been produced with lattice mismatch ≤0.21%.
    Applied Physics Letters 03/2012; 100(11). · 3.52 Impact Factor
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    ABSTRACT: Replacing small amounts of As with Bi in InGaBiAs/InP induces large decreases and increases in the bandgap, Eg, and spin-orbit splitting, ΔSO, respectively. The possibility of achieving ΔSO>;Eg and a reduced temperature (T) dependence for Eg are significant for suppressing recombination losses and improving performance in mid-infrared photonic devices. We measure Eg(x, T) and ΔSO(x, T) in In0.53Ga0.47BixAs1-x/InP samples for 0≤x≤0.032 by optical spectroscopy. While we find no clear evidence of a decreased dEg/dT (≈0.33±0.07meV/K in all samples) we find ΔSO>;Eg for x>;3.3-4.3%. The predictions of a valence band anti-crossing model agree well with the measurements.
    Photonics (ICP), 2012 IEEE 3rd International Conference on; 01/2012
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    ABSTRACT: InGaAs lattice-matched to InP was grown by molecular beam epitaxy with randomly distributed TbAs nanoparticles for thermoelectric power generation applications. TbAs:InGaAs is expected to have a large thermoelectric figure of merit, ZT, particularly at high temperatures, owing to energy band alignment between the nanoparticles and their surrounding matrix. Here, the room temperature thermoelectric properties were measured as a function of TbAs concentration, revealing a maximum thermoelectric power factor of 2.38 W/mK{sup 2} and ZT of 0.19 with 0.2% TbAs. Trends in the thermoelectric properties closely resemble those found in comparable ErAs:InGaAs nanocomposite materials. However, nanoparticles were not observed by scanning transmission electron microscopy in the highest ZT TbAs:InGaAs sample, unlike the highest ZT ErAs:InGaAs sample (0.2% ErAs) and two higher concentration TbAs:InGaAs samples examined. Consistent with expectations concerning the positioning of the Fermi level in these materials, ZT was enhanced by TbAs incorporation largely due to a high Seebeck coefficient, whereas ErAs provided InGaAs with higher conductivity but a lower Seebeck coefficient than that of TbAs:InGaAs. Thermal conductivity was reduced significantly from that of intrinsic thin-film InGaAs only with TbAs concentrations greater than {approx}1.7%.
    Journal of Applied Physics 01/2012; 111:094312. · 2.19 Impact Factor
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    ABSTRACT: Terbium-doped InGaAs with a high terbium concentration shows promise as a high-efficiency thermoelectric material, with the thermal conductivity dropping to 1.27 W/m K at a TbAs concentration of 1.55% by number of atoms. However, large discrepancies are noted in Hall effect measurements on terbium-doped InGaAs grown by molecular beam epitaxy on InP substrate following standard III–V wet chemical processing techniques, when compared to samples with no processing beyond deposition of indium contacts. These discrepancies preclude systematic exposition of temperature- and composition-dependent thermoelectric figures of merit. The discrepancy is seen to be correlated with the terbium concentration and the thickness of the active material. The steps in the process sequence are examined under controlled conditions. Although the exact cause for the discrepancy has not been found, some of the obvious reasons have been ruled out. It is therefore surmised that (1) chemical reaction with photoresist, (2) ultraviolet irradiation during photolithography, or (3) reaction with photoresist developing solutions and HF are the factors responsible for the changes in Hall voltage. Evidence is presented for the creation of surface states that corrupt Hall effect measurements on the bulk semiconductor.
    Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 01/2012; 30(3):031508-031508-6. · 2.14 Impact Factor
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    ABSTRACT: Energies of E0 and E0 + ΔSO transitions in In0.53Ga0.47BixAs1−x alloys with 0 < x ≤ 0.036 have been studied by contactless electroreflectance spectroscopy at room temperature. It has been clearly observed that the E0 transition shifts to longer wavelengths (∼50 meV/% of Bi), while the E0 + ΔSO transition is approximately unchanged with changes in Bi concentration. These changes in the energies of optical transitions are discussed in the context of the valence band anticrossing model as well as the common anion rule applied to III-V semiconductors.
    Applied Physics Letters 12/2011; 99(25). · 3.52 Impact Factor
  • Dmitri O. Klenov, Joshua M. O. Zide
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    ABSTRACT: The structure of epitaxially grown InAlAs/InP interfaces was studied using atomically resolved x-ray energy dispersive spectroscopy in scanning transmission electron microscopy. As and P sublattices show sharp termination on the interface. The In sublattice is continuous across the interface. The study has shown the depletion of the Al concentration at the interface; at the last atomic columns of the InAlAs, In occupancy is close to 100%, while Al occupancy is almost zero. A monolayer of InAs at the interface is consistent with substitution of As for P at the surface preceding growth.
    Applied Physics Letters 10/2011; 99(14). · 3.52 Impact Factor
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    ABSTRACT: Rare-earth impurities in III–V semiconductors are known to self-assemble into semimetallic nanoparticles which have been shown to reduce lattice thermal conductivity without harming electronic properties. Here, we show that adjusting the band alignment between ErAs and In0.53Ga0.47−XAlXAs allows energy-dependent scattering of carriers that can be used to increase thermoelectric power factor. Films of various Al concentrations were grown by molecular beam epitaxy, and thermoelectric properties were characterized. We observe concurrent increases in electrical conductivity and Seebeck coefficient with increasing temperatures, demonstrating energy-dependent scattering. We report the first simultaneous power factor enhancement and thermal conductivity reduction in a nanoparticle-based system, resulting in a high figure of merit, ZT = 1.33 at 800 K.
    Journal of Applied Physics 09/2011; 110(5). · 2.19 Impact Factor

Publication Stats

2k Citations
224.14 Total Impact Points

Institutions

  • 2008–2014
    • University of Delaware
      • • Department of Materials Science and Engineering
      • • Department of Electrical and Computer Engineering
      Delaware, United States
    • Yonsei University
      • Department of Mechanical Engineering
      Seoul, Seoul, South Korea
  • 2004–2011
    • University of California, Santa Barbara
      • Department of Electrical and Computer Engineering
      Santa Barbara, CA, United States
  • 2009
    • University of Illinois, Urbana-Champaign
      • Department of Materials Science and Engineering
      Urbana, IL, United States
    • University of California, Santa Cruz
      • Department of Electrical Engineering
      Santa Cruz, CA, United States
  • 2007
    • Boston University
      • Department of Physics
      Boston, Massachusetts, United States
  • 2006–2007
    • Los Alamos National Laboratory
      • • Center for Integrated Nanotechnologies
      • • Materials Physics and Applications Division
      Los Alamos, California, United States