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13 Apr 1998

Volume 72, Issue 15, pp. 1799-1928

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Improved reliability of red GaInP vertical-cavity surface-emitting lasers using bias-induced annealing

Robert W. Herrick and Pierre M. Petroff

Appl. Phys. Lett. 72, 1799 (1998); http://dx.doi.org/10.1063/1.121320 (3 pages) | Cited 8 times

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We have used a bias-induced annealing process to improve the initial performance and the reliability of red (680 nm) Ga.46In.54P vertical-cavity surface-emitting lasers. Measurements showed improved cathodoluminescence efficiency and increased current collection efficiency after the anneal. Trap concentration is believed to be reduced by the bias-induced annealing process. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
61.72.Cc Kinetics of defect formation and annealing
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Plastic microring lasers on fibers and wires

S. V. Frolov, Z. V. Vardeny, and K. Yoshino

Appl. Phys. Lett. 72, 1802 (1998); http://dx.doi.org/10.1063/1.121189 (3 pages) | Cited 37 times

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Photopumped, pulsed, narrow line laser emission is demonstrated using cylindrical microcavities formed by π-conjugated polymer thin films wrapped around thin glass optical fibers and metal wires with various diameters D. A variety of cavity-dependent resonant laser mode structures were observed, which for D<10 μm contain a single resonant spectral line of less than 1 Å in width. The microring lasers are also characterized by a well-defined, very low threshold excitation intensity, at which beam directionality and polarization degree dramatically increase. These findings open up the fields of lasers and fiber optics to organic materials. © 1998 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Wc Optical coatings
42.55.Rz Doped-insulator lasers and other solid state lasers

Radiation-enhanced network formation in copolymer galvanoforms for diffractive nickel x-ray optics with high aspect ratios

D. Weiss, M. Peuker, and G. Schneider

Appl. Phys. Lett. 72, 1805 (1998); http://dx.doi.org/10.1063/1.121190 (3 pages) | Cited 21 times

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High-resolution x-ray microscopy makes use of nanostructured diffractive optics such as Fresnel zone plates made of nickel. These micro zone plates are manufactured using microscopic galvanoforms and electrodeposition techniques. Copolymer galvanoforms for nickel micro zone plates were irradiated with high doses of x-ray radiation to increase the degree of cross-linking of the copolymer network; in this way, exact pattern replication in the galvanoform was obtained for zone aspect ratios of up to 8:1. Using these galvanoforms, nickel micro zone plates were produced for the soft x-ray wavelength λ=2.4 nm, with smallest zone widths of 30 nm and 40 nm, achieving first-order diffraction efficiencies of up to 13% and 20%, respectively. © 1998 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
81.15.Pq Electrodeposition, electroplating
81.05.Bx Metals, semimetals, and alloys
82.45.-h Electrochemistry and electrophoresis

Visible dual-wavelength light generation in optical superlattice Er:LiNbO3 through upconversion and quasi-phase-matched frequency doubling

Jian-jun Zheng, Yan-qing Lu, Gui-peng Luo, Jing Ma, Ya-lin Lu, Nai-ben Ming, Jing-liang He, and Zu-yan Xu

Appl. Phys. Lett. 72, 1808 (1998); http://dx.doi.org/10.1063/1.121191 (3 pages) | Cited 20 times

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Optical superlattice Er:LiNbO3 was fabricated by inducing a periodic ferroelectric domain structure into the crystal during the growing process. Because of the combination of the nonlinear optical properties of LiNbO3 and the spectral properties of Er3+, the crystal can simultaneously emit the second harmonic light through quasi-phase matching and the green light through upconversion at room temperature. Pumped by infrared diode lasers, violet-and-green and blue-and-green light generation was demonstrated in two samples. The detailed absorption spectrum and emission spectrum of upconversion were measured. The possible physical mechanism was discussed. © 1998 American Institute of Physics.
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78.66.Nk Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
77.80.Dj Domain structure; hysteresis
42.79.Nv Optical frequency converters

Pump intensity profiling of vertical-cavity surface-emitting lasers using near-field scanning optical microscopy

G. H. Vander Rhodes, J. M. Pomeroy, M. S. Ünlü, B. B. Goldberg, K. J. Knopp, and D. H. Christensen

Appl. Phys. Lett. 72, 1811 (1998); http://dx.doi.org/10.1063/1.121192 (3 pages) | Cited 3 times

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We have mapped the internal pump intensity distribution of an optically pumped vertical-cavity surface-emitting laser. Spontaneous emission from quantum wells placed throughout the distributed Bragg reflectors is correlated to the pump intensity. The emission is monitored along the cleaved edge using the high spatial resolution and shallow depth of field provided by near-field scanning optical microscopy. Our results show a distinct buildup of optical intensity between the mirror stacks. Simulations performed using the transfer matrix method match well with the experimental data. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Minimum temperature sensitivity of 1.55 μm vertical-cavity lasers at −30 nm gain offset

J. Piprek, Y. A. Akulova, D. I. Babic, L. A. Coldren, and J. E. Bowers

Appl. Phys. Lett. 72, 1814 (1998); http://dx.doi.org/10.1063/1.121318 (3 pages) | Cited 41 times

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Double-fused vertical-cavity surface-emitting lasers (VCSELs) have demonstrated the highest temperature performance of any 1.5 μm VCSEL, but further optimization is needed to reduce their temperature sensitivity. We present and analyze threshold current measurements of these devices between −90 °C and 30 °C stage temperature. Despite a zero gain peak offset from the emission wavelength at room temperature, the pulsed threshold current has its minimum near −50 °C corresponding to about −30 nm gain offset. This is in contrast to a common VCSEL design rule. Temperature effects on the optical gain of the strain-compensated InGaAsP/InP active region are found to be the main cause for the disagreement. A design rule modification is proposed. Numerical simulation of an optimized 1.55 μm VCSEL shows that gain offset improvements are counteracted by loss mechanisms. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Large third-order optical nonlinearity in Au:TiO2 composite films measured on a femtosecond time scale

H. B. Liao, R. F. Xiao, H. Wang, K. S. Wong, and G. K. L. Wong

Appl. Phys. Lett. 72, 1817 (1998); http://dx.doi.org/10.1063/1.121193 (3 pages) | Cited 92 times

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The wavelength dependence of the third-order nonlinear optical susceptibilities, χ(3), of the Au:TiO2 composite films with Au concentration varying from 15% to 60% (volume fraction), was measured by a degenerate four-wave mixing (DFWM) technique using a probe laser with a pulse width of 200 fs. It was found that, with the wavelength of the probe laser close to the surface plasmon resonance ( ∼ 680 nm), both the χ(3) and the figure of merit, χ(3)/α (α is optical absorption coefficient) were significantly enhanced. The maximum value of the χ(3) was 6×10−7 esu and occurred at an Au concentration of about 38%. Femtosecond time-resolved DFWM measurements revealed that the response time of the optical nonlinearity in the Au:TiO2 films is extremely fast. The time-resolved DFWM results suggest that the main physical mechanism involved in the optical nonlinearity in Au:TiO2 films on the femtoseconds time scale is the interband electric–dipole transition, and the hot electron excitation only partially contributes to the χ(3) on the femtosecond time scale and it becomes dominant only in the picosecond region. © 1998 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.47.-p Spectroscopy of solid state dynamics
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Optical data storage in semi-insulating GaAs

V. Alex and J. Weber

Appl. Phys. Lett. 72, 1820 (1998); http://dx.doi.org/10.1063/1.121194 (3 pages) | Cited 4 times

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We observe a light-induced on–off switching of the selective donor–acceptor pair excitation in bulk-grown semi-insulating GaAs. The spectral dependence of the switching process is related to the metastability of the EL2 defect. In the ground state, this As-antisite related midgap donor compensates the shallow acceptors and is responsible for the semi-insulating properties of the material. The loss of the shallow acceptor compensation, that accompanies the transfer of the EL2 to its metastable state leads to the observed absorption and luminescence quench of the shallow donor–acceptor pairs. We exploit these effects in demonstrating optical data storage in semi-insulating GaAs. © 1998 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
78.55.Cr III-V semiconductors
42.70.Gi Light-sensitive materials

Red shift of plasmon resonance frequency due to the interacting Ag nanoparticles embedded in single crystal SiO2 by implantation

Zhengxin Liu, Honghong Wang, Hao Li, and Xuemei Wang

Appl. Phys. Lett. 72, 1823 (1998); http://dx.doi.org/10.1063/1.121196 (3 pages) | Cited 72 times

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A metal nanoparticle system has been prepared by 200 Kev Ag+ ion implantation into perfect single crystal SiO2 at room temperature to dose: 6.7×1016/cm2. The system presents quasidual-layer structure: the shallower implanted layer containing noninteracting small Ag nanoparticles and the deeper layer containing interacting large nanoparticles, in which great red shift, about 1 eV, comparing with the plasmon resonance frequency of the noninteracting nanoparticle, can be clearly observed. The red shift is attributed to the multipoles interaction among the high density nanoparticles at external electric field. Moreover, the magnitude of red shift increases with implanted dose. © 1998 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.72.up Other materials
78.40.Ha Other nonmetallic inorganics
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
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Kinetic model for plasma-based ion implantation of a short, cylindrical tube with auxiliary electrode

T. E. Sheridan, T. K. Kwok, and P. K. Chu

Appl. Phys. Lett. 72, 1826 (1998); http://dx.doi.org/10.1063/1.121188 (3 pages) | Cited 23 times

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Plasma-based ion implantation of the inner surface of a short, cylindrical tube is modeled using a two-dimensional particle-in-cell simulation. An auxiliary electrode, here a coaxial anode, is used to increase the ion impact energy. Initially, ions inside the tube impact the inner surface at approximately normal angles. At later times, ions enter the tube from the exterior plasma and impact predominantly near its center at glancing angles. Ions are found to cross the midplane of the tube and in some cases to pass completely through the tube, in contrast to the predictions of the “collisionless” fluid model. The total incident dose is greatest around the center of the tube, and least at its ends. © 1998 American Institute of Physics.
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61.72.up Other materials
52.40.Hf Plasma-material interactions; boundary layer effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition

Angle-resolved energy distributions of laser ablated silver ions in vacuum

Tue N. Hansen, Jørgen Schou, and James G. Lunney

Appl. Phys. Lett. 72, 1829 (1998); http://dx.doi.org/10.1063/1.121197 (3 pages) | Cited 23 times

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The energy distributions of ions ablated from silver in vacuum have been measured in situ for pulsed laser irradiation at 355 nm. We have determined the energy spectra for directions ranging from 5° to 75° with respect to the normal in the intensity range from 100 to 400 MW/cm2. At the highest intensity and for angles close to the normal, the highest ion energy measured exceeds 500 eV. However, the energy distributions are shifted strongly towards low energies with increasing angle. © 1998 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
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Surface anisotropy of polyimide film irradiated with linearly polarized ultraviolet light

K. Sakamoto, K. Usami, M. Watanabe, R. Arafune, and S. Ushioda

Appl. Phys. Lett. 72, 1832 (1998); http://dx.doi.org/10.1063/1.121198 (3 pages) | Cited 18 times

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Using polarized infrared (IR) absorption, we have investigated the surface anisotropy of a poly [4, 4′-oxydiphenylene-pyromellitimide] (PMDA-ODA) film that arises from anisotropic decomposition of the polyimide chain during irradiation with linearly polarized ultraviolet (LPUV) light. To monitor the surface anisotropy, we designed the sample structure so that the polyimide films decomposed uniformly over the entire film thickness. The surface anisotropy has a maximum at an irradiation energy of 105 J/cm2. For PMDA-ODA, the maximum surface anisotropy is significantly smaller than the surface anisotropy generated by rubbing. By analyzing the irradiation energy dependence of an IR absorption band, we found that the decomposition rate of the polyimide chain oriented parallel to the polarization direction of the LPUV light is greater only by ∼23% than that oriented perpendicular to it. This is the reason for the small surface anisotropy induced by the LPUV light irradiation. © 1998 American Institute of Physics.
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61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.50.-m Photochemistry

Silicon nanowires prepared by laser ablation at high temperature

Y. F. Zhang, Y. H. Tang, N. Wang, D. P. Yu, C. S. Lee, I. Bello, and S. T. Lee

Appl. Phys. Lett. 72, 1835 (1998); http://dx.doi.org/10.1063/1.121199 (3 pages) | Cited 228 times

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Silicon nanowires have been synthesized in high yield and high purity by using a high-temperature laser-ablation method with growth rates ranging from 10 to 80 μm/h. Transmission electron microscopic investigation shows that the nanowires are crystalline Si, and have diameters ranging from 3 to 43 nm and length up to a few hundreds microns. Twins and stacking faults have been observed in the Si core of the nanowires. The lattice structure and constant of the nanowires as determined from x-ray diffraction (XRD) are nearly identical to those of bulk Si, although the relative XRD peak intensities are different from those of randomly oriented Si crystallites. Raman scattering from the nanowires shows an asymmetric peak at the same position as that of bulk crystalline silicon. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
61.72.Nn Stacking faults and other planar or extended defects
78.30.Am Elemental semiconductors and insulators

Significant reduction of cathodoluminescent degradation in sulfide-based phosphors

J. M. Fitz-Gerald, T. A. Trottier, R. K. Singh, and P. H. Holloway

Appl. Phys. Lett. 72, 1838 (1998); http://dx.doi.org/10.1063/1.121195 (2 pages) | Cited 33 times

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The degradation of cathodoluminescent (CL) brightness under prolonged electron-beam excitation of phosphors has been identified as one of the outstanding critical issues for flat-panel field-emission displays. In this letter, we have demonstrated that a TaSi2 coating on Y2O2S:Eu3+ phosphors substantially inhibits the cathodoluminescent degradation characteristics without reducing its efficiency. The coating was deposited by pulsed laser deposition of TaSi2 targets onto a fluidized bed containing phosphor particles. Cathodoluminescent degradation experiments conducted at 2 keV and at 150 μA/cm2, showed that the CL brightness decreased by more than 50% after a Coulomb load of 15 C/cm2 on the uncoated material. In contrast, the TaSi2-coated phosphor powders showed much less degradation, with CL brightness only decreasing by approximately 12% after electron irradiation with the same dose. © 1998 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Fg Pulsed laser ablation deposition

Creation of nanometer-scale patterns with selected metal films

Jon T. Moore, Paul D. Beale, Thomas A. Winningham, and Kenneth Douglas

Appl. Phys. Lett. 72, 1840 (1998); http://dx.doi.org/10.1063/1.121200 (3 pages) | Cited 6 times

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We demonstrate the utilization of various transition metals in a biologically derived, nanometer-scale patterning process. This process created large arrays of nanometer-scale dots (nanodot arrays) with several of these metals. The correlation between nanodot array formation and the interaction energies between metal atoms, other metals atoms, and the surface of the sample was explored. The behavior of the metal films was then investigated with the aid of a Monte Carlo solid-on-solid simulation. © 1998 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
07.79.Lh Atomic force microscopes
87.64.Dz Scanning tunneling and atomic force microscopy

Direct transformation of graphite to cubic diamond observed in a laser-heated diamond anvil cell

H. Yusa, K. Takemura, Y. Matsui, H. Morishima, K. Watanabe, H. Yamawaki, and K. Aoki

Appl. Phys. Lett. 72, 1843 (1998); http://dx.doi.org/10.1063/1.121201 (3 pages) | Cited 13 times

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Graphite samples are heated in a diamond anvil cell with a CO2 laser above 11 GPa. A light transparent phase has appeared after heating, which is quenchable at ambient conditions. The Raman spectrum shows that the phase is a fine-grained cubic diamond. Images by a high resolution transmission electron microscope indicate that the diamond has twins and stacking faults of nanometer size. The electron diffraction pattern shows that the stacking fault cannot be explained by a diamond polytype such as a hexagonal diamond. The cathodoluminescence pattern exhibits the “band-A” emission, which is derived from the defects of the cubic diamond. © 1998 American Institute of Physics.  
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81.05.ub Fullerenes and related materials
81.40.Vw Pressure treatment
64.70.K- Solid-solid transitions
61.72.Nn Stacking faults and other planar or extended defects
78.30.Am Elemental semiconductors and insulators
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Chemical interactions at Ta/fluorinated polymer buried interfaces

G.-R. Yang, Y.-P. Zhao, B. Wang, E. Barnat, J. McDonald, and T.-M. Lu

Appl. Phys. Lett. 72, 1846 (1998); http://dx.doi.org/10.1063/1.121202 (2 pages) | Cited 17 times

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In this letter, we study Ta/parylene-F (PA–F) buried interfaces using x-ray photoelectron spectroscopy. We found that the Ta–F bond was formed at the Ta/PA–F interface after depositing a layer of thin Ta film (<50 Å). For the Ar+ or O2 plasma pretreated PA–F surface, in addition to the Ta–F bond, a Ta–C bond was observed at the buried interface after Ta metallization. The Ta–C bond may be responsible for the enhancement of Ta/PA–F adhesion. © 1998 American Institute of Physics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Gy Mechanical properties; surface strains
85.40.Ls Metallization, contacts, interconnects; device isolation
79.60.Jv Interfaces; heterostructures; nanostructures
61.41.+e Polymers, elastomers, and plastics

Influence of potential fluctuation on optical and electrical properties in GaN

Eunsoon Oh, Hyeongsoo Park, and Yongjo Park

Appl. Phys. Lett. 72, 1848 (1998); http://dx.doi.org/10.1063/1.121203 (3 pages) | Cited 22 times

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We observed strong correlation between optical properties and transport properties in GaN. Both the intensity and the energy of near-band edge photoluminescence (PL) peak in GaN:Si vary with its mobility. Such behavior has been explained by the potential fluctuation associated with the inhomogeneous impurities or local defects, leading to the space-charge scattering of carriers and the redshift of the PL line. We also discuss the strain relaxation in GaN:Si. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance

Conduction in nonstoichiometric molecular-beam epitaxial GaAs grown above the critical thickness

P. Kordoš, M. Marso, and M. Luysberg

Appl. Phys. Lett. 72, 1851 (1998); http://dx.doi.org/10.1063/1.121204 (3 pages) | Cited 3 times

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Different conduction behavior is observed in nonstoichiometric (NS) molecular-beam epitaxial GaAs grown at 200 °C below and above the critical thickness. In the low-field Ohmic region only the monocrystalline part of the layer contributes to the room-temperature resistivity, but at higher temperatures the resistivity scales with the total layer thickness. In NS GaAs grown above the critical thickness, a superlinear J–Vn (n = 2–3) dependence is found at intermediate fields. The prebreakdown voltage is proportional to the total thickness. This indicates that different defects control the electrical properties of the polycrystalline and monocrystalline parts of the NS GaAs. These results can be useful in the design of NS GaAs based devices, which operate at higher temperature and/or higher electric fields. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys

Temperature-independent transport in high-mobility pentacene transistors

S. F. Nelson, Y.-Y. Lin, D. J. Gundlach, and T. N. Jackson

Appl. Phys. Lett. 72, 1854 (1998); http://dx.doi.org/10.1063/1.121205 (3 pages) | Cited 390 times

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The charge-carrier transport mechanism in the organic semiconductor pentacene is explored using thin-film transistor structures. The variation of the field-effect mobility with temperature differs from sample to sample, ranging from thermally activated to temperature-independent behavior. This result excludes thermally activated hopping as the fundamental transport mechanism in pentacene thin films, and suggests that traps and/or contact effects may strongly influence the observed characteristics. These results also indicate that field-effect transistors may not be appropriate vehicles for illuminating basic transport mechanisms in organic materials. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds

Luminescence of as-grown and thermally annealed GaAsN/GaAs

S. Francoeur, G. Sivaraman, Y. Qiu, S. Nikishin, and H. Temkin

Appl. Phys. Lett. 72, 1857 (1998); http://dx.doi.org/10.1063/1.121206 (3 pages) | Cited 95 times

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We report a study of the luminescence properties of coherently strained GaAs1−xNx grown on GaAs by metalorganic molecular beam epitaxy. Well-defined photoluminescence was observed in samples with a nitrogen concentration up to 3%. Samples subjected to thermal anneals, investigated by x-ray diffraction and photoluminescence, show increased nitrogen incorporation and significant improvements in the luminescence efficiency. A band-gap reduction of more than 400 meV, compared to GaAs, is observed for a nitrogen concentration of ∼ 3%. For the range of nitrogen concentrations investigated here, the band gap follows predictions of the dielectric model of Van Vechten [J. A. Van Vechten and T. K. Bergstresser, Phys. Rev. B 1, 3351 (1970), and references therein]. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
61.72.Cc Kinetics of defect formation and annealing

1.3 μm photoresponsivity in Si-based Ge1−xCx photodiodes

Xiaoping Shao, S. L. Rommel, B. A. Orner, H. Feng, M. W. Dashiell, R. T. Troeger, J. Kolodzey, Paul R. Berger, and Thomas Laursen

Appl. Phys. Lett. 72, 1860 (1998); http://dx.doi.org/10.1063/1.121207 (3 pages) | Cited 2 times

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Ge1−xCx/Si heterostructure photodiodes with nominal carbon percentages (0 ⩽ x ⩽ 0.02), which exceed the solubility limit, were grown by solid source molecular beam epitaxy on n-type (100) Si substrates. The p-Ge1−xCx/n-Si photodiodes were fabricated and tested. The p-Ge1−xCx/n-Si junction exhibits diode rectification with a reverse saturation current of about 10 pA/μm2 at −1 V and high reverse breakdown voltage, up to −80 V. A significant reduction in diode reverse leakage current was observed by adding C to Ge, but these effects saturated with more C. Photoresponsivity was observed from these Si-based p-Ge1−xCx/n-Si photodiodes at a wavelength of ⩾1.3 μm, compatible with fiber optic wavelengths. External quantum efficiency of these thin surface-normal photodetectors was measured up to 2.2%, which decreased as the carbon percentage was increased. © 1998 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

The Schottky energy barrier dependence of charge injection in organic light-emitting diodes

I. H. Campbell, P. S. Davids, D. L. Smith, N. N. Barashkov, and J. P. Ferraris

Appl. Phys. Lett. 72, 1863 (1998); http://dx.doi.org/10.1063/1.121208 (3 pages) | Cited 57 times

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We present device model calculations of the current–voltage (I–V) characteristics of organic diodes and compare them with measurements of structures fabricated using MEH-PPV. The structures are designed so that all of the current is injected from one contact. The I–V characteristics are considered as a function of the Schottky energy barrier to charge injection from the contact. Experimentally, the Schottky barrier is varied from essentially zero to more than 1 eV by using different metal contacts. A consistent description of the device I–V characteristics is obtained as the Schottky barrier is varied from small values, less than about 0.4 eV, where the current flow is space-charge limited to larger values where it is contact limited. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.Kk Junction diodes
79.40.+z Thermionic emission

Temperature dependence of the Fermi level in low-temperature-grown GaAs

Y. H. Chen, Z. Yang, Z. G. Wang, and R. G. Li

Appl. Phys. Lett. 72, 1866 (1998); http://dx.doi.org/10.1063/1.121209 (3 pages) | Cited 9 times

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A variable-temperature reflectance difference spectroscopy study of GaAs grown by molecular beam epitaxy at low-temperature GaAs (LT-GaAs) shows that the Fermi level is mostly determined by the point defects in samples annealed at below 600 °C and can be shifted by photoquenching the defects. The Fermi level is otherwise almost temperature independent, leading to an estimated width of the defect band of 150 meV in the as-grown sample. For LT-GaAs annealed at 850 °C, the Fermi level is firmly pinned, most likely by the As precipitates. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.20.Nr Semiconductor compounds
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Electronic structures at the interfaces between copper phthalocyanine and layered materials

T. Shimada, K. Hamaguchi, A. Koma, and F. S. Ohuchi

Appl. Phys. Lett. 72, 1869 (1998); http://dx.doi.org/10.1063/1.121210 (3 pages) | Cited 27 times

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Copper phtalocyanine (CuPc) films with the thickness controlled in molecular scales have been grown epitaxially on (0001) surfaces of layered materials, and electronic interaction at the interfaces have been studied by photoelectron spectroscopy. Materials with different electronic properties having different work functions (Evac) were chosen as the substrates; semiconducting MoTe2 (Evac=4.0 eV), semi-metallic highly oriented pyrolytic graphite (Evac=4.5 eV) and metallic TaSe2 (Evac=5.5 eV). Formation of interface dipole layers was found at CuPc/TaSe2 interfaces and molecular orbitals involved were identified. © 1998 American Institute of Physics.
Show PACS
73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions
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