Joshua M. O. Zide

University of Delaware, Ньюарк, Delaware, United States

Are you Joshua M. O. Zide?

Claim your profile

Publications (102)236.81 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We propose and systematically justify a band structure for TbAs nanoparticles in GaAs and In0.53Ga0.47As host matrices. Fluence-dependent optical-pump terahertz-probe measurements suggest the TbAs nanoparticles have a band gap and provide information on the carrier dynamics, which are determined by the band alignment. Spectrophotometry measurements provide the energy of optical transitions in the nanocomposite systems and reveal a large blue shift in the absorption energy when the host matrix is changed from In0.53Ga0.47As to GaAs. Finally, Hall data provides the approximate Fermi level in each system. From this data, we deduce that the TbAs:GaAs system forms a type I (straddling) heterojunction and the TbAs:In0.53Ga0.47As system forms a type II (staggered) heterojunction.
    Applied Physics Letters 09/2015; 107(10). DOI:10.1063/1.4930816 · 3.30 Impact Factor
  • Eoin P O'Reilly · Stephen J Sweeney · Shumin Wang · Joshua M O Zide ·

    Semiconductor Science and Technology 09/2015; 30(9). DOI:10.1088/0268-1242/30/9/090301 · 2.19 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Temperature dependent photo-modulated reflectance is used to measure the band gap E g and spin–orbit splitting energy Δ so in dilute-Bi In0.53Ga0.47As1-x Bix /InP for 1.2% ≤ x ≤ 5.8%. At room temperature, E g decreases with increasing Bi from 0.65 to 0.47 eV (∼2.6 μm), while Δ so increases from 0.42 to 0.62 eV, leading to a crossover between E g and Δ so around 3.8% Bi. The 5.8% Bi sample is the first example of this alloy where Δ so > E g has been confirmed at all temperatures. The condition Δ so > E g is important for suppressing hot-hole-producing non-radiative Auger recombination and inter-valence band absorption losses and so holds promise for the development of mid-infra-red devices based on this material system. The measured variations of E g and Δ so as a function of Bi content at 300 K are compared to those calculated using a 12-band k.p Hamiltonian which includes valence band anti-crossing effects. The E g results as a function of temperature are fitted with the Bose–Einstein model. We also look for evidence to support the prediction that E g in dilute bismides may show a reduced temperature sensitivity, but find no clear indication of that.
    Semiconductor Science and Technology 09/2015; 30(9). DOI:10.1088/0268-1242/30/9/094015 · 2.19 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The thermal stability of Si dopants incorporated during growth and via ion implantation was investigated as a function of annealing time and temperature. Ion implanted samples show a maximum achievable doping concentration of 1.4×1019 cm-3. Growth doped samples exhibit higher post growth electrical activations than achievable in ion implanted samples but subsequent thermal processing at 750°C for 10 minutes is shown to deactivate heavily doped (3×1019 cm-3) MBE doped substrates to the same active doping concentration of 1.4×1019 cm-3 suggesting a common thermodynamic limit to Si activation in InGaAs.
    ECS Transactions 05/2015; 66(7):23-27. DOI:10.1149/06607.0023ecst
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effect of thermal annealing on the net donor concentration and diffusion of Si in In0.53Ga0.47As is compared for electrically active layers formed by ion implantation versus molecular beam epitaxy (MBE). Upon thermal treatment at temperatures of 700 °C or higher for 10 min, both ion implanted and growth-doped substrates converge to a common net donor solubility. These results indicate that while MBE doped substrates typically exhibit higher active concentrations relative to implanted substrates, the higher active Si concentrations from MBE growth are metastable and susceptible to deactivation upon subsequent thermal treatments after growth. Active Si doping concentrations in MBE doped material and ion-implanted materials are shown to converge toward a fixed net donor solubility limit of 1.4 × 1019 cm−3. Secondary ion mass spectroscopy of annealed samples indicates that the diffusivity of Si in MBE doped substrates is higher than those of ion implanted substrates presumably due to concentration-dependent diffusion effects.
    03/2015; 33(2):021206. DOI:10.1116/1.4914319
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Although methods for harvesting subbandgap solar photons have been demonstrated, present approaches still face substantial challenges. We evaluate carrier escape mechanisms in an InAs/GaAs quantum dot (QD) intermediate band photovoltaic (PV) device using photocurrent measurements under subbandgap illumination. We show that subbandgap photons can generate photocurrent through a two-photon absorption process, but that carrier trapping and retrapping limit the overall photocurrent regardless of whether the dominant carrier escape mechanism is optical, tunneling, or thermal. We introduce a new design for an InAs QD-based nanostructured material that can efficiently upconvert two low-energy photons into one high-energy photon. Efficiency is enhanced by intentionally sacrificing a small amount of photon energy to minimize radiative and nonradiative loss. Upconversion PV devices based on this approach separate the absorption of subbandgap photons from the current-harvesting junction, circumventing the carrier-trapping problems.
    IEEE Journal of Photovoltaics 01/2015; 5(1):224-228. DOI:10.1109/JPHOTOV.2014.2367865 · 3.17 Impact Factor
  • [Show abstract] [Hide abstract]
    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 12/2014; 10(23). DOI:10.1002/smll.201400891 · 8.37 Impact Factor
  • [Show abstract] [Hide abstract]
    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(10-10):103108. DOI:10.1063/1.4895519 · 3.30 Impact Factor
  • Source

  • [Show abstract] [Hide abstract]
    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). DOI:10.1103/PhysRevB.89.045418 · 3.74 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We show that thermoelectrics can generate power from environments experiencing temporal temperature fluctuations; this source of power is useful for low-power devices in remote locations. We design and characterize devices that employ a thermoelectric module sandwiched between two heat exchangers with significantly different thermal masses and examine the effects of heat exchanger size and material selection, period of oscillation of the environmental temperature fluctuations, and radiative heat transfer on the thermoelectric power output. We report maximum experimental power generation on the order of milliwatts using standard bismuth telluride thermoelectric modules in devices with a size of about 10 cm(3).
    Energy 10/2013; 60:453. DOI:10.1016/ · 4.84 Impact Factor
  • Source
    Y. Zhong · P. B. Dongmo · L. Gong · S. Law · B. Chase · D. Wasserman · J. M. O. Zide ·
    [Show abstract] [Hide abstract]
    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). DOI:10.1364/OME.3.001197 · 2.84 Impact Factor
  • Cory C. Bomberger · Peter M. Attia · Ajay K. Prasad · Joshua M.O. Zide ·
    [Show abstract] [Hide abstract]
    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. DOI:10.1016/j.applthermaleng.2013.02.039 · 2.74 Impact Factor
  • [Show abstract] [Hide abstract]
    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). DOI:10.1063/1.4804937 · 2.18 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    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 05/2013; 102(18):182108. DOI:10.1063/1.4802841 · 3.30 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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). DOI:10.1063/1.4768262 · 2.18 Impact Factor
  • [Show abstract] [Hide abstract]
    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). DOI:10.1063/1.4761996 · 2.18 Impact Factor
  • [Show abstract] [Hide abstract]
    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). DOI:10.1063/1.4754514 · 2.18 Impact Factor

Publication Stats

2k Citations
236.81 Total Impact Points


  • 2008-2015
    • University of Delaware
      • • Department of Materials Science and Engineering
      • • Department of Mechanical Engineering
      • • Department of Electrical and Computer Engineering
      Ньюарк, Delaware, United States
  • 2004-2011
    • University of California, Santa Barbara
      • Department of Electrical and Computer Engineering
      Santa Barbara, California, United States
  • 2006
    • Los Alamos National Laboratory
      • Center for Integrated Nanotechnologies
      Лос-Аламос, California, United States