Erbium Arsenide Research Articles

Analysis of ErAs nanoparticle surface grown using a two-step modified diffusion length process

Erbium arsenide nanoparticles (ErAs NPs) grown using a two-step modified diffusion length growth process are studied. The process consists of a low diffusion length (LDL) deposition step for nucleation followed by a high diffusion length (HDL) deposition step for the growth of existing nuclei without forming new nuclei. With the LDL and HDL growth conditions properly coordinated, independent control over the NP size is demonstrated over a wide range of NP densities (14–309 NP/μm2). This control is attributed to the change of Péclet number between the LDL and HDL steps, which enables complete capture of the adatoms by the existing nuclei. The appropriate LDL and HDL growth conditions are identified for practical applications of the process. Given the uniqueness of the process, the ErAs nucleus critical size (∼7 Er atoms) is derived in the nucleation regime in the LDL step exhibiting consistency with the previous observation for ErAs NP growth.

Estimate of the plasmonic enhancement for the erbium arsenide (metallic nanoparticle): indium arsenide (quantum dot) system

The epitaxially grown system comprising semimetallic ErAs (erbium arsenide) nanoparticles (MNP) and InAs (indium arsenide) single quantum dots (QDs) hold great promise for plasmonic applications. The distinguishing feature of the ErAs-InAs hybrid is that the hybrid separation can be varied and accurately controlled in the molecular-beam epitaxial growth. In order to assess the potential of this system for plasmonic applications, this paper aims to estimate and optimize the expected magnitude of the plasmonic enhancement. We use the Sun–Khurghin theory to estimate the expected absorption and photoluminescence (PL) enhancement. Using a carefully selected set of materials’ parameters as input, we predict about 500-fold plasmonic PL enhancement for this system under resonant conditions.

Carrier transfer from InAs quantum dots to ErAs metal nanoparticles

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.

Role of Atomic Multiplets in the Electronic Structure of Rare-Earth Semiconductors and Semimetals

We present a study of the effects of strong correlations in rare-earth pnictides, in which localized 4f states simultaneously retain atomiclike character and strongly influence the free-electron-like valence electron states. Using erbium arsenide as our example, we use a modern implementation of dynamical mean-field theory to obtain the atomic multiplet structure of the Er3+ 4f shell, as well as its unusually strong coupling to the electronic Fermi surfaces; these types of behavior are not correctly described within conventional electronic-structure methods. We are then able to explain the long-standing theoretical question of the quasisaturation of magnetization in an applied magnetic field, and to obtain the first quantitative agreement with experimental Shubnikov-de Haas frequencies of the Fermi-surface sheets.

6 Watt Segmented Power Generator Modules using Bi2Te3 and (InGaAs)1-x(InAlAs)x Elements Embedded with ErAs Nanoparticles

AbstractWe report the fabrication and characterization of segmented element power generator modules of 16 x 16 thermoelectric elements consisting of 0.8 mm thick Bi2Te3 and 50 μm thick ErAs:(InGaAs)1-x(InAlAs)x with 0.6% ErAs by volume. Erbium Arsenide metallic nanoparticles are incorporated to create scattering centers for middle and long wavelength phonons, and to form local potential barriers for electron filtering. The thermoelectric properties of ErAs:(InGaAs)1-x(InAlAs)x were characterized in terms of electrical conductivity and Seebeck coefficient from 300 K up to 830 K. Generator modules of Bi2Te3 and ErAs:(InGaAs)1-x(InAlAs)x segmented elements were fabricated and an output power of 6.3 W was measured. 3D finite modeling shows that the performance of thermoelectric generator modules can further be enhanced by the improvement of the thermoelectric properties of the element materials, and reducing the electrical and thermal parasitic losses.

Segmented Power Generator Modules of Bi2Te3 and ErAs:InGaAlAs Embedded with ErAs Nanoparticles

AbstractWe report the fabrication and characterization of segmented element power generator modules of 254 thermoelectric elements. The element is 1 mm × 1 mm in area, which consists of 300 μm thickness Bi2Te3 and 50 μm thickness ErAs:(InGaAs)1-x(InAlAs)x, so that each segment can work at different temperature ranges. Erbium arsenide metallic nanoparticles are incorporated to create scattering centers for middle and long wavelength phonons, provide charge carriers, and form local Schottky barriers for electron filtering. The thermoelectric properties of ErAs:InGaAlAs were characterized by variable temperature measurements of thermal conductivity, electrical conductivity and Seebeck coefficient from 300 K to 600 K. Generator modules of Bi2Te3 and ErAs:InGaAlAs segmented elements were fabricated and an output power over 5.5 W was measured. The performance of the thermoelectric generator modules can further be improved by improving the thermoelectric properties of the element material, and reducing the electrical and thermal parasitic losses.

400 element ErAs:InGaAs/InGaAlAs superlattice power generator

ABSTRACTWe report the fabrication and characterization of thin film power generators composed 400 p- and n-type ErAs:InGaAs/InGaAlAs superlattice thermoelectric elements. The thermoelectric elements incorporate erbium arsenide metallic nanoparticles into the semiconductor superlattice structure to provide charge carriers and create scattering centers for phonons. 10 µm p- and n-type InGaAs/InGaAlAs superlattices with embedded ErAs nano-particles were grown on InP substrates using molecular beam epitaxy. Thermal conductivity values were measured using the 3ω method and cross-plane Seebeck coefficients were determined using Seebeck device test patterns. 400 element ErAs:InGaAs/InGaAlAs thin film power generators were fabricated from superlattice elements 10 µm thick and 200 µm × 200 µm in area. The output power was 4.7 milliwatts for an external electrical load resistor of 150 Ω at about 80 K temperature difference drop across the generator. We discuss the limitations to the generator's performance and provide suggestions for further improvement.

HYBRIDIZATION BETWEEN 4f-5d STATES IN ErAs(100)

Generally in both elemental and compound rare earth systems, the 4f levels are treated as core states with little interaction with the 5d hybrid conduction and valence band states. In the present study, the band dispersions of the rare-earth pnictide erbium arsenide ( ErAs ) are observed to be perturbed from this expectation. Both photoemission symmetry selection rules and ab initio calculations provide evidences of the 4f - 5d hybridization. This finding is also supported by the f–f resonant transition excitation energy shifts in characteristic electron-energy-loss spectroscopy (EELS).

Electronic structure of ErAs(100)

The experimental band structure of the rare-earth pnictide erbium arsenide (ErAs), grown epitaxially on GaAs(100), has been mapped out using photoelectron spectroscopy and inverse photoemission spectroscopy. The electronic structure is dominated by bulk bands qualitatively consistent with the calculated band structure. A number of additional nondispersing $4f$ multiplet levels can be identified in the valence-band structure as well as at least one surface resonance band. From symmetry selection rules, photoemission provides strong evidence that the ${\ensuremath{\Delta}}_{5}$ (or e) symmetry bands are a consequence of hybridization between Er and As, while the ${\ensuremath{\Delta}}_{1}$ (or ${a}_{1})$ symmetry bands have possible contributions from nonbonding or antibonding states from Er (and/or As).

Properties and Growth of MBE Grown Erbium Doped Gallium Arsenide Co-Doped with Selenium

AbstractThe growth of erbium doped GaAs by molecular beam epitaxy (MBE) can, depending on growth conditions, result in the precipitation of small spherical particles of erbium arsenide. It has been observed that by reducing the V:III (As:Ga) flux ratio to close to stoichiometry wirelike precipitates roughly aligned in the direction of growth are produced. The concentration of erbium incorporated into the GaAs lattice for a constant erbium flux is also affected by the As:Ga flux ratio with an increase in erbium doping being observed with decreasing As:Ga flux ratio.Electrical measurements have been performed on erbium doped GaAs samples co-doped with selenium, an n-type dopant. Measurements have revealed that when erbium is present, the electron concentration is reduced by an amount approximately equal to 70% of the erbium concentration. DLTS measurements have shown that although large concentrations of deep levels are present in erbium doped material, the measured concentration of these deep levels is not high enough to account for the observed reduction in electron concentration with erbium doping.

Self-organizing growth of erbium arsenide quantum dots and wires in gallium arsenide by molecular beam epitaxy

Gallium arsenide doped with erbium has been grown by molecular beam epitaxy. At growth temperatures in the range 540–605 °C, and with arsenic to gallium flux ratios of 2 and more, the erbium forms uniform crystalline microprecipitates of ErAs when the concentration exceeds 7×1017 cm−3. The diameter can be varied in the range 11–21 Å by altering the growth temperature. Reducing the arsenic to gallium flux ratio to close to stoichiometry changes the growth mode to one yielding quantum wires aligned in the growth direction. Subtle changes in growth conditions lead to bifurcated structures, which we refer to as quantum trees.

Erbium Doped Gallium Arsenide a Self-Organising Low Dimensional System

ABSTRACTThe growth of erbium doped gallium arsenide by MBE at normal substrate temperatures (∼580°C) is constrained by a solubility limit of 8×1017 cm−3. This is much less than is desirable for optical emitters using the forbidden 4f transitions of Er3+ to produce radiation at 1.54μm. We have developed an MBE technique where it is possible to produce spherical mesoscopic precipitates containing erbium as a matrix element within the gallium arsenide. Structural and analytical studies indicate that the precipitate is cubic (rock salt) erbium arsenide. The physical size of the precipitates is self limiting as a result of surface migration occurring during MBE growth. By adjusting the growth conditions it is possible to produce an array of uniform erbium arsenide quantum dots of a size chosen from the range 10-20Å. The dot density can be varied by changing the erbium flux.