Er Films Research Articles

Growth and morphology of Er-doped GaN on sapphire and hydride vapor phase epitaxy substrates

We report the morphological and compositional characteristics and their effect on optical properties of Er-doped GaN grown by solid source molecular beam epitaxy on sapphire and hydride vapor phase epitaxy GaN substrates. The GaN was grown by molecular beam epitaxy on sapphire substrates using solid sources (for Ga, Al, and Er) and a plasma gas source for N2. The emission spectrum of the GaN:Er films consists of two unique narrow green lines at 537 and 558 nm along with typical Er3+ emission in the infrared at 1.5 μm. The narrow lines have been identified as Er3+ transitions from the H11/22 and S3/24 levels to the I15/24 ground state. The morphology of the GaN:Er films showed that the growth resulted in either a columnar or more compact structure with no effect on green light emission intensity.

Photoluminescence properties of erbium-doped single-crystal and porous silicon films

The features of the photoluminescence spectra of single-crystal and porous Si:Er films grown by molecular beam epitaxy are discussed.

Synthesis of colloids and films of Pr, Er and Yb with nonaqueous solvents

Colloidal dispersions of Yb, Er and Pr have been prepared by chemical liquid deposition. The metals were cocondensed at 77 K with 2-methoxyethanol and ethanol to produce solvated metal atoms. The particle size of the dispersions was determined by transmission electron microscopy to range from 52 to 1080 A; the particles had spherical shapes. After solvent evaporation under vacuum, active solids and amorphous powder were deposited over Cu and Al metal. Dispersion stability, particle size, UV/Vis absorption and zeta potential were studied. The solids prepared by solvent evaporation were characterized by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The films prepared on Al were studied by scanning electron microscopy. The most stable colloid was obtained using 2-methoxyethanol: several concentrations were stable for several months and the zeta potential indicated that this colloid stability is mainly due to solvation effects. FTIR spectroscopy of the solids indicated solvent incorporation in the film. This observation was corroborated by thermal analysis. Information on the thermal stability of the films was obtained by TGA. The UV/Vis absorption spectrum was measured at several concentrations under different conditions.

Magnetic coupling in amorphous Co–Er films

Amorphous Co100−XErX thin films have been prepared by rf sputtering and their magnetic properties have been studied. The mean field theory has been used to explain the temperature dependence of the magnetization. High-field magnetization studies performed at 4.2 K in magnetic fields up to 5.5 T on amorphous Co100−XErX alloys have revealed, for samples with stoichiometry close to that of a compensated ferrimagnet, a magnetic behavior that is characteristic of a noncollinear magnetic structure of the Er and Co sublattices. From the noncollinear regime the exchange interactions between the Co and Er magnetic sublattices have been accurately evaluated.

Optical and Structural Properties of Er3+-Doped GaN Grown by MBE

We report the morphological and compositional characteristics of Er-doped GaN grown by MBE on Si(111) substrates and their effect on optical properties. The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. The films emit by photoexcitation in the visible and near infrared wavelengths from the Er atomic levels. The morphology of the GaN:Er films was examined by AFM. Composition was determined by SIMS depth profiling that revealed a large Er concentration at 4.5×1021 atoms/cm3 accompanied by a high oxygen impurity concentration.

Visible and Infrared Emission from GaN:Er Thin Films Grown by Sputtering

AbstractErbium-doped films were grown on sapphire and silicon substrates by reactive sputtering, with different Er concentrations in the film. GaN films deposited at 800 K were determined to be polycrystalline by x-ray diffraction analysis, and retained their polycrystalline structure after annealing in nitrogen at 1250 K. The Er-doped films showed optical transmission beginning at about 360 nm, and the Er dose and film purity were determined with Rutherford backscattering spectroscopy. Photoluminescence and cathodoluminescence spectroscopy showed sharp emission lines corresponding to Er 3+ intra 4fn shell transitions over the range from 9 – 300 K. At above-bandgap optical and electron excitation, the 4S3/2 and 4F9/2 transition dominate, and are superposed on the “yellow band” emission. The infrared emission line at 1543 nm, corresponding to the Er 4I⅓ to 4I3/2 transition is also observed.

Design and Synthesis of a 33-Layer Narrow Bandpass Filter with Graded Refractive Index Profiles

AbstractA novel bandp ass filter consisting of graded refractive index profiles and a three-cavity stack was designed. It exhibits good optical characteristics, i.e., high transmittance (>99%) at the designated wavelength of 1550±25 nm and high reflectance (>99%) in wavelength regions of 1400±50 nm and 1780±100 nm. This designed 33-layer TiO2-SiO2 film with graded refractive index profiles was prepared by helicon plasma sputtering. The measured transmittance spectrum exhibited good agreement with the designed spectrum. The microstructure of this multilay er film was investigated using electron microscopy.

1.54 μm Emission of pulsed-laser deposited Er-doped films on Si

We investigate the photoluminescence properties of Er-doped SiO 2 and glass films fabricated by pulsed-laser deposition (PLD) for different deposition parameters and erbium host materials. The luminescence yield of SiO 2 : Er films increases strongly with increasing oxygen background pressure during laser ablation. We compare SiO 2 and soda-lime glass as host materials for erbium ions. Under identical growth conditions and the same erbium concentrations in both targets, films deposited from the soda-lime glass show a much higher luminescence yield. This enhancement is attributed to a higher concentration of optically active erbium in the multicomponent glass environment.

Magnetic phase diagram of Ho/Er alloys

The magnetic structures of a series of Ho/Er alloys have been determined by neutron-diffraction techniques. The alloys were prepared as thin films (10 000 \AA{} thick) by molecular beam epitaxy, and are single crystals with a mosaic spread of about 0.2$\ifmmode^\circ\else\textdegree\fi{}$. A variety of magnetic structures are found, arising from the competition between the exchange and anisotropic crystal-field interactions, the latter of which are of opposite sign for Ho and Er. The magnetic phase diagram has five distinct phases with long-range magnetic order: basal-plane helical, tilted helical, cycloidal, $c$-axis longitudinally modulated, and conical. The cycloid and tilted helix have both incommensurate and commensurate $q$=$\frac{1}{4}$${c}^{*}$ forms, and all of the thin films have a conical structure at low temperatures, even though corresponding films of pure Ho and Er do not exhibit this phase. There is a pentacritical point, and probably a disordered phase which is completely surrounded in the phase diagram by magnetic phases with long-range order. A Landau theory is developed to describe these results.

Optical and Structural Properties of Er3+-Doped GaN Grown by MBE

AbstractWe report the morphological and compositional characteristics of Er-doped GaN grown by MBE on Si(111) substrates and their effect on optical properties. The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Er) and a plasma gas source for N2. The films emit by photoexcitation in the visible and near infrared wavelengths from the Er atomic levels. The morphology of the GaN:Er films was examined by AFM. Composition was determined by SIMS depth profiling that revealed a large Er concentration at 4.5 × 1021 atoms/cm3 accompanied by a high oxygen impurity concentration.

Incorporation Of Er Into GaN By in-situ Doping During Halide Vapor Phase Epitaxy

ABSTRACTThe incorporation of Er into GaN by in-situ doping during halide vapor phase epitaxy has been investigated. The NH3, HCl, metallic Ga and Er were used as source materials, while N2 was employed as a carrier gas. The GaN:Er films were obtained at different Ga/Er source temperatures. The SIMS analysis shows that the steady state Er doping concentration can be as high as 2×1018 cm−3. All in-situ Er-doped samples luminescence at 1.54 μm due to the 4I13/2 → 4I15/2 transition of Er3+ at both low (11K) and room temperature. The higher the Ga/Er boat temperature, the stronger the 1.54 μm luminescence, implying a higher incorporation rate of Er into the GaN. The 4I11/2 → 4I15/2 transition luminescence, centered around 980 nm, can also be detected at both low and room temperature. The broad-spectrum PL measurements exhibited sharp bandedge luminescence without the presence of the yellow luminescence band.

Growth kinetics of amorphous interlayers and formation of crystalline silicide phases in ultrahigh vacuum deposited polycrystalline Er and Tb thin films on (001)Si

The growth kinetics of amorphous interlayer (a-interlayer) and formation of crystalline silicide phases in ultrahigh vacuum deposited polycrystalline Er and Tb thin films on (001)Si have been investigated by cross-section transmission electron microscopy. The growth of the amorphous interlayer in both Er/Si and Tb/Si systems was observed to exhibit similar behaviors. The growth was found to follow a linear growth law initially in samples annealed at 190–240 °C. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 0.5 eV, 15.5 nm, and 0.35 eV, 16 nm in Er/Si and Tb/Si systems, respectively. Crystalline silicides (ErSi2−x or TbSi2−x) were found to form at the amorphous interlayer/Si interfaces in samples after prolonged and/or high-temperature annealing. Simultaneous growth of the a-interlayer and crystalline phase was observed and the growth rate of a-interlayer was faster than the growth of epitaxial ErSi2−x and TbSi2−x phases in samples annealed at 270–300 °C in Er/Si and Tb/Si systems, respectively. The competitive growth can be understood from energetic consideration. A high density of recessed amorphous regions were found to form between isolated epitaxial silicide regions which led to uneven silicide/Si interfaces and eventually pinholes in the silicide films at high temperatures. The formation mechanism of rough silicide/Si interface is discussed.

Photoluminescence study of Er-doped AlN

We present a photoluminescence (PL) study of Er-doped AlN epilayer on sapphire substrate. The AlN : Er film was grown by metalorganic molecular beam epitaxy and an Er concentration of 2–5 × 10 19Er/cm 3 was obtained. Following the excitation of an argon ion laser at 488 nm, we observed a strong 1.54 μm Er 3+ luminescence, which is quenched by only a factor of two between 15 K and room temperature. The photoluminescence excitation (PLE) spectrum, as well as PL lifetime measurement suggest that at 488 nm, Er 3+ is excited through a photo-carrier mediated process. In contrast, exciting AlN : Er at ~525 nm seems to result in the direct excitation of an intra-4f transition of Er 3+.

Photo-, cathodo-, and electroluminescence from erbium and oxygen co-implanted GaN

Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implanted n-type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range (0.01–5)×1015 ions/cm2 and O doses (0.1–1)×1016 ions/cm2. GaN films implanted with 2×1015 Er2+/cm2 at 350 keV and co-implanted with 1016 O+/cm2 at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800 °C (45 min) or at 900 °C (30 min) in flowing NH3. The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly (20%) less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95±0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35±0.12, 2.15±0.11, and 1.74±0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation (reverse biased light emitting diode), respectively. The cross sections for Er in GaN were estimated to be 4.8×10−21 cm2 for direct optical excitation at 983 nm and 4.8×10−16 cm2 for impact excitation. The cross-section values are believed to be within a factor of 2–4.

Er doping of AlN during growth by metalorganic molecular beam epitaxy

The doping of AlN during growth by metalorganic molecular beam epitaxy with an Er effusion source has resulted in AlN:Er films exhibiting strong room-temperature 1.54 μm photoluminescence (PL). The luminescence detected in the AlN:Er grown during this study was orders of magnitude greater in intensity than that from ion-implanted samples and represents the first demonstration of strong emission from rare-earth doped, epitaxial group III nitrides. Secondary ion mass spectroscopy was used to verify a dynamic range for this doping technique of 3×1017–2×1021 Er cm−3 with varying effusion cell temperature. The effects of growth temperature on Er incorporation and segregation behavior were also determined. PL studies, including room-temperature and thermal quenching experiments, were conducted.

Optoelectronic properties of transition metal and rare earth doped epitaxial layers on InP for magneto-optics

Rare earth-and transition metal-doped thin films of InP, In0.53Ga0.47As, and In0.71Ga0.29As0.58P0.42 were grown by liquid phase epitaxy and evaluated for use in integrated electro-optical and magneto-optical applications, such as waveguides and Faraday rotators. The films were lattice matched to (100) InP substrates, and the transition metal (Mn) and rare earth (Gd, Eu, and Er) doping concentra-tions were between 2.6 × 1018 and 1.5 × 1020 cm-3. The chemical profiles were generally found to be homogeneous by SIMS, although in more highly doped films the rare earths were observed to segregate toward the interfaces. The undoped films were n-type, and the net carrier concentrations in the rare earth-doped (Gd, Eu, Er) films were decreased by an order of magnitude. The Mn-doped films were p-type. Optically, the rare earth dopants were observed to raise the refractive index of the layers at 632.8 nm, and subsequent waveguiding in doped InP layers was observed at 1.3 μm. Although the Faraday rotations of our materials were much less than that of well known oxides, such as yttrium iron garnet, they were sufficient for device applications, and our materials can be much more easily integrated with InP OEIC devices. For example, a 1 cm waveguide would provide the large rotation (45°) required in isolator applica-tions.

20S human proteasomes bind with a specific orientation to lipid monolayers in vitro

20S Proteasomes are non-lysosomal, high molecular weight proteinases implicated in the degradation of misfolded proteins and several short-lived regulatory proteins. They have a well established role, as the core of the 26S proteasome complex, in the ubiquitin-dependent proteolytic pathway and in antigen processing. While correctly folded proteins are not degraded by the 20S proteasome, unfolding, for example by oxidation, may render them degradable. The 20S proteasome is a 700-kDa cylindrical particle, composed of 14 subunits of molecular masses 20–35 kDa. There is evidence that 20S proteasomes are in close proximity to or associate with the endoplasmic reticulum and nuclear and plasma membranes in vivo. To better understand the lipid association of 20S proteasomes in vitro, we used a lipid monolayer system as a simple model system for biological membranes. The structure and orientation of the monolayer lipid bound 20S proteasomes has been determined by electron microscopy. 20S proteasomes associated in an ‘end-on’ configuration specifically on PI lipid monolayers forming large arrays, with their channels opposite the lipid headgroups. On ER and Golgi lipid films 20S proteasones were oriented in the same way as on the PI lipid film but were monodisperse. Protein molecules were randomly oriented in the presence of PA, PG, PS, PC and mitochondrial lipid monolayers. We show that 20S proteasomes bind to phospholipids in vitro in a preferred orientation which places the proteasome channel perpendicular to the membrane.

Characteristics and device applications of erbium doped III-V semiconductors grown by molecular beam epitaxy

We have studied the properties of molecular beam epitaxially (MBE)-grown Erdoped III-V semiconductors for optoelectronic applications. Optically excited Er3+ in insulating materials exhibits optical emission chiefly around 1.54 μm, in the range of minimum loss in silica fiber. It was thought, therefore, that an electrically pumped Er-doped semiconductor laser would find great applicability in fiber-optic communication systems. Exhaustive photoluminescence (PL) characterization was conducted on several of As-based III-V semiconductors doped with Er, on bulk as well as quantum-well structures. We did not observe any Errelated PL emission at 1.54 μm for any of the materials/structures studied, a phenomenon which renders impractical the realization of an Er-doped III-V semiconductor laser. Deep level transient spectroscopy studies were performed on GaAs and AlGaAs co-doped with Er and Si to investigate the presence of any Er-related deep levels. The lack of band-edge luminescence in the GaAs:Er films led us to perform carrier-lifetime measurements by electro-optic sampling of photoconductive transients generated in these films. We discovered lifetimes in the picosecond regime, tunable by varying the Er concentration in the films. We also found the films to be highly resistive, the resistivity increasing with increasing Er-concentration. Intensive structural characterization (double-crys-tal x-ray and transmission electron microscopy) performed by us on GaAs:Er epilayers indicates the presence of high-density nanometer-sized ErAs precipitates in MBE-grown GaAs:Er. These metallic nanoprecipitates probably form internal Schottky barriers within the GaAs matrix, which give rise to Shockley-Read-Hall recombination centers, thus accounting for both the high resistivities and the ultrashort carrier lifetimes. Optoelectronic devices fabricated included novel tunable (in terms of speed and responsivity) high-speed metal-semiconductor-metal (MSM) photodiodes made with GaAs:Er. Pseudomorphic AlGaAs/ InGaAs modulation doped field effect transistors (MODFETs) (for high-speed MSM-FET monolithically integrated optical photoreceivers) were also fabricated using a GaAs:Er buffer layer which substantially reduced backgating effects in these devices.

Properties of Ion Implanted and UHV-CVD Grown Si:Er

AbstractWe have fabricated Si:Er films by ion implantation and ultra-high vacuum chemical vapor deposition (UHV-CVD). The energy of the ion implantation was varied from 200 keV to 4.5 MeV. Oxygen was co-implanted to overlap the erbium profile. At implant energies of 400 keV, we found that the luminescence was optimized at a lower annealing temperature (800° C, 30 minutes) than that needed for the 4.5 MeV implant (900°C, 30 minutes). The light intensity per erbium atom is critically dependent on the implantation energy. However, spreading resistance measurements show that the donor activity of the implanted erbium is independent of energy. We have correlated the donor activity with quantum efficiency by varying the donor spatial distribution and concentration through post implantation heat treatments.For the UHV-CVD grown Si:Er films, two erbium metallorganic precursors, Er(TMHD)3 and Er(FOD)3. have been used for growths from 550–620°C. The thickness of the erbium layers are similar to that of implanted devices but the Er concentration of 4 × 1021/cm3 exceeded the implanted material by two orders of magnitude.

Electroluminescence of Erbium in Oxygen Doped Silicon

AbstractIt is demonstrated room-temperature electroluminescence at 1.54 μm in erbiumimplanted oxygen doped silicon (27 at. 0), due to intra-4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal-(Si:O,Er)-p+ silicon diodes. The 30 nm thick Si:O,Er films are amorphous layers deposited onto silicon substrates by chemical vapour deposition of SiH4 and N20, doped by ion implantation with Er to a concentration up to ≈ 1.5 at.%, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400°C in reverse bias under breakdown condition and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O,Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross-section of ≈6×10−16 cm2 is obtained.