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26 Jul 2004

Volume 85, Issue 4, pp. 513-696

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 642 (2004); http://dx.doi.org/10.1063/1.1776327 (3 pages)

Zhijun Sun and Hong Koo Kim
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Effects of carbon nanosolids on the electro-optical properties of a twisted nematic liquid-crystal host

Wei Lee, Chun-Yu Wang, and Yu-Cheng Shih

Appl. Phys. Lett. 85, 513 (2004); http://dx.doi.org/10.1063/1.1771799 (3 pages) | Cited 87 times

Online Publication Date: 23 July 2004

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We present results of the electro-optical effect in 90° twisted nematic cells of pristine and doped liquid crystals under an applied dc voltage. The doped cells were fabricated with a minute addition of either buckminsterfullerene C60 or multiwalled carbon nanotubes (CNTs). Investigated were the switching behaviors as well as the hystereses and time evolutions of both the optical transmittance and electrical capacitance of the display samples. It is shown that doping with nanotubes can effectively reduce the dc driving voltage and improve the switching behavior.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals
78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices

Strong blue photoluminescence from as-fabricated amorphous-Si:H∕SiO2 multilayers

Zhongyuan Ma, Kunji Chen, Xinfan Huang, Jun Xu, Wei Li, Da Zhu, Jiaxin Mei, Feng Qiao, and Duan Feng

Appl. Phys. Lett. 85, 516 (2004); http://dx.doi.org/10.1063/1.1775878 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2004

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Amorphous-Si:H∕SiO2 multilayers were layer-by-layer deposited and in situ plasma oxidized by a plasma-enhanced chemical vapor deposition system. Blue photoluminescence at room temperature was observed from as-fabricated samples without annealing. By controlling the thickness of the amorphous-Si:H sublayer from 4 to 1.5 nm, the photoluminescence peak blueshifts from 466 to 437 nm. Strong and stable photoluminescence could be observed by the naked eye for all the samples. Based on the analysis of microstructure and absorption spectra, the mechanism of the blue photoluminescence was discussed.
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68.65.Ac Multilayers
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments

Millimeter-wave, terahertz, and mid-infrared transmission through common clothing

J. E. Bjarnason, T. L. J. Chan, A. W. M. Lee, M. A. Celis, and E. R. Brown

Appl. Phys. Lett. 85, 519 (2004); http://dx.doi.org/10.1063/1.1771814 (3 pages) | Cited 38 times

Online Publication Date: 23 July 2004

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This letter reports electromagnetic transmission measurements through cloth samples from eight types of fabrics common in garments and baggage. The transmission at millimeter-wave and terahertz frequencies was measured with a custom ErAs:GaAs tunable photomixing spectrometer. The IR transmission between 3 and 8 μm was measured with a Fourier-transform infrared spectrometer. All samples were usefully transparent at millimeter-wave frequencies (up to 300 GHz) based on a 3 dB criterion, but became progressively opaque at higher frequencies in a highly sample-dependent manner. This is explained by the samples becoming “optically dense” in the THz region, so that the transmission becomes exponentially dependent on sample thickness. The attenuation in the IR region is very high (⩾25 dB) except in two samples (rayon and nylon), whose exceptional transparency (e.g., −12 dB in nylon) is attributed to pores intrinsic to the material.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.25.Bs Wave propagation, transmission and absorption

InP photonic crystal membrane structures: Fabrication accuracy and optical performance

Aimin Xing, Marcelo Darvanco, Daniel J Blumenthal, and Evelyn L Hu

Appl. Phys. Lett. 85, 522 (2004); http://dx.doi.org/10.1063/1.1776336 (3 pages)

Online Publication Date: 23 July 2004

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Two-dimensional photonic crystal membranes with coupled ridge waveguides were fabricated in InP∕InGaAsP by using e-beam lithography and reactive ion etching. The optical transmission characteristics were measured and a photonic band gap with better than 20 dB extinction ratio was observed. The band-gap dependence on radius-to-lattice constant ratio (r∕a) was numerically and experimentally investigated. Predictable, accurate placement of the band edge by varying r∕a is demonstrated.
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81.05.Ea III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Qs Photonic bandgap materials

Broad-area laser diode with 0.02 nm bandwidth and diffraction limited output due to double external cavity feedback

Jun Chen, Xiaodong Wu, Jianhong Ge, Andreas Hermerschmidt, and Hans Joachim Eichler

Appl. Phys. Lett. 85, 525 (2004); http://dx.doi.org/10.1063/1.1774248 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2004

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External cavity feedback for a broad-area laser diode (BAL) with antireflection coating on the front facet is investigated experimentally. The feedback is created by a high-reflection mirror and a blazed grating, which reflect two parts of the laser emission back to the BAL, thereby forming an external resonator. When a Fabry–Perot etalon was inserted into the resonator an output beam with a bandwidth of 0.02 nm and power of 150 mW was obtained. The beam diffraction limited factor amounted to M2=1.16.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Dj Gratings
42.79.Wc Optical coatings
42.79.Bh Lenses, prisms and mirrors

Fullerenes surface gratings for liquid crystal alignment

Mara Talarico, Giovanni Carbone, Riccardo Barberi, and Attilio Golemme

Appl. Phys. Lett. 85, 528 (2004); http://dx.doi.org/10.1063/1.1774249 (3 pages) | Cited 9 times

Online Publication Date: 23 July 2004

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We report on the formation of surface structures by photopolymerization of C60 and C70 in isotropic solutions. The structures show the same periodicity of the interference patterns used for photopolymerization and behave as diffraction gratings. Mass spectrometry confirmed that the deposited material contains polymerized fullerenes, while the structure of the deposit was investigated by atomic force microscopy. We have also shown that these periodic structures are useful for inducing mesophase orientation.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
42.79.Dj Gratings
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.50.-m Photochemistry

AlGaN-based 280 nm light-emitting diodes with continuous wave powers in excess of 1.5 mW

W. H. Sun, J. P. Zhang, V. Adivarahan, A Chitnis, M. Shatalov, S. Wu, V. Mandavilli, J. W. Yang, and M. A. Khan

Appl. Phys. Lett. 85, 531 (2004); http://dx.doi.org/10.1063/1.1772864 (3 pages) | Cited 28 times

Online Publication Date: 23 July 2004

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We report on AlGaN-based light-emitting diodes over sapphire with peak emission at 280 nm. A modified active layer structure consisting of four multiple quantum wells, addition of an electron blocking magnesium doped p-AlGaN layer, improved contacts along with flip-chip packaging resulted in a cw power of 0.7 mW at 230 mA for a single 200 μm×200 μm device. Flip-chipping four 100 μm×100 μm devices in a parallel configuration improved the dc saturation current and enabled us to obtain a cw power of 1.53 mW (at 450 mA) and a pulse power as high as 24 mW (at 1.5 A). These powers translate to values of 0.36% and 0.12% for the external quantum efficiency and the wall plug efficiency.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

High-performance photorefractive polymers sensitized by cadmium selenide nanoparticles

Canek Fuentes-Hernandez, Duck Jong Suh, Bernard Kippelen, and Seth R. Marder

Appl. Phys. Lett. 85, 534 (2004); http://dx.doi.org/10.1063/1.1771451 (3 pages) | Cited 27 times

Online Publication Date: 23 July 2004

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We report on efficient and fast hybrid photorefractive polymer sensitized with cadmium selenide (CdSe) quantum dots. The surface of the quantum dots was treated with 4-methylbenzenethiol. This surfactant is responsible for efficient photoinduced charge generation in the composite, leading to fast grating build-up times of 100 ms and below. Overmodulation of the diffraction efficiency was observed at an applied field of 60 V∕μm.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Dj Gratings

Interband type-II miniband-to-bound state diode lasers for the midinfrared

C. Mermelstein, J. Schmitz, R. Kiefer, M. Walther, and J. Wagner

Appl. Phys. Lett. 85, 537 (2004); http://dx.doi.org/10.1063/1.1775287 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2004

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A design for midinfrared diode lasers based on interband type-II miniband-to-bound state transitions is proposed and has been demonstrated experimentally. Type-II miniband-to-bound state laser structures emitting at 3.25 μm with active regions consisting of 5 and 10 W periods were grown by solid-source molecular-beam epitaxy and processed into ridge waveguide lasers. Substrate-side down mounted devices with a 10 period active region and uncoated facets could be operated in continuous-wave (cw) mode up to 185 K and as high as 260 K in pulsed mode. A high characteristic temperature of 100 K has been achieved for heat-sink temperatures below 140 K, decreasing to 33 K for the 140 to 185 K interval. At 110 K, a 5 period laser structure exhibited a threshold current density of 177 A∕cm2 and a slope efficiency of 61 mW∕A. Single-ended output powers of 144 mW in cw mode and exceeding 330 mW in pulsed operation were obtained for a substrate-side down mounted 5 period diode laser with high-reflection∕antireflection coated mirror facets, operated at 110 K.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Ea III-V semiconductors
42.79.Wc Optical coatings
68.65.Cd Superlattices
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Ultrafast all-optical switching at 1.55 μm using an organic multilayer device

Satoshi Tatsuura, Takashi Matsubara, Minquan Tian, Hiroyuki Mitsu, Izumi Iwasa, Yasuhiro Sato, and Makoto Furuki

Appl. Phys. Lett. 85, 540 (2004); http://dx.doi.org/10.1063/1.1775290 (3 pages) | Cited 9 times

Online Publication Date: 23 July 2004

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We report ultrafast all-optical switching at optical communication wavelength using a device with a layered structure containing organic films. Spin-coated layers of di(benzofuranonyl)methanolate (BM) derivative are formed alternately with vacuum evaporated layers of germanium (II) oxide. An optical Kerr shutter is constructed using this BM multilayer with 1.55 μm signal and 1.63 μm gate pulses of 100 fs time durations. As a result, optical switching with signal-to-noise ratio over 20 dB is attained at gate-pulse intensity above 30 pJ∕μm2 and a response time comparable to pulse width is observed. The BM multilayer could be an efficient optical communication device for parallel data processing.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Wc Optical coatings
42.25.Gy Edge and boundary effects; reflection and refraction

Negative effective permeability in polaritonic photonic crystals

Kerwyn Casey Huang, M. L. Povinelli, and John D. Joannopoulos

Appl. Phys. Lett. 85, 543 (2004); http://dx.doi.org/10.1063/1.1775291 (3 pages) | Cited 52 times

Online Publication Date: 23 July 2004

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We find that a two-dimensional photonic crystal composed of polaritonic materials behaves as an effective medium with negative permeability in the micron wavelength range. The resonance in μeff is due to the large values of ϵ(ω) attained near the transverse phonon frequency ωT. The minimal wavelength for achieving an effective permeability less than −1 in a LiTaO3 crystal, obtained by optimizing the rod size and the lattice constant, is around 12 μm, a range previously inaccessible using dielectric metamaterials. For certain dissipation levels, we find that other polaritonic media also exhibit a resonant effect with μeff<−1 for wavelengths ranging from 2 to ∼100 μm.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
63.20.-e Phonons in crystal lattices
77.22.Ch Permittivity (dielectric function)
42.70.Qs Photonic bandgap materials

Multiplex nonresonant pump four-wave mixing

Eun Seong Lee, Dae Sik Choi, Jae Yong Lee, and Jae Won Hahn

Appl. Phys. Lett. 85, 546 (2004); http://dx.doi.org/10.1063/1.1775293 (3 pages) | Cited 4 times

Online Publication Date: 23 July 2004

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We propose a scheme of multiplex nonresonant pump four-wave mixing (NRP-FWM) process which is highly immune to saturation problems. The process is accomplished with two high-intensity pump beams detuned far from the resonance of the sample under investigation and a resonant probe beam as weak as possible not to give rise to nonlinear absorption. Only a single-broadband probe beam is used for the multiplex experiment to detect the electronic swan band spectrum of C2 molecules in a premixed acetylene–oxygen flame. Comparing the signal of the degenerate four-wave mixing (DFWM) experiment on the same sample, we found that the signal level at which the NRP-FWM starts to show saturation is about 250 times higher than in the case of the DFWM.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
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Ultrahigh-speed etching of SiO2 with ultrahigh selectivity over Si in microwave-excited non equilibrium atmospheric pressure plasma

Koji Yamakawa, Masaru Hori, Toshio Goto, Shoji Den, Toshirou Katagiri, and Hiroyuki Kano

Appl. Phys. Lett. 85, 549 (2004); http://dx.doi.org/10.1063/1.1775885 (3 pages) | Cited 20 times

Online Publication Date: 23 July 2004

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Etching of a SiO2 film [Boro-phospho silicate glass (BPSG)] has been performed in a continuous-wave microwave-excited nonequilibrium atmospheric pressure plasma using a microgap discharge. A NF3∕He gas mixture with added H2O was employed as the feed gas. An ultrahigh etch rate for SiO2 (BPSG) of 14 μm∕min and an ultrahigh selectivity over Si(SiO2∕Si) of 200 was obtained. A mechanism for the selective etching is proposed based on results obtained using Fourier transform infrared spectroscopy and spatially imaged optical emission spectroscopy with an intensified charge-coupled device camera. This process could offer a breakthrough for ultrahigh-speed, damage-free micromachining of SiO2 in microelectromechanical system devices.
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81.65.Cf Surface cleaning, etching, patterning
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses
78.66.-w Optical properties of specific thin films
52.25.-b Plasma properties
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Evidence for a vacancy and interstitial mediated diffusion of As in Si and Si0.9Ge0.1

Suresh Uppal, Arthur F. W. Willoughby, Janet M. Bonar, and Jing Zhang

Appl. Phys. Lett. 85, 552 (2004); http://dx.doi.org/10.1063/1.1775883 (3 pages) | Cited 9 times

Online Publication Date: 23 July 2004

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Arsenic diffusion has been studied at 1000°C in Si and relaxed Si0.9Ge0.1 structures grown using molecular beam epitaxy. Intrinsic diffusivity of As in Si0.9Ge0.1 is shown to be enhanced over Si by a factor of 2, in agreement with the literature. Using selective point defect injection, obtained by surface reactions achieved using rapid thermal annealing process under oxygen atmosphere, clear evidence of the participation of both vacancy and interstitial defects in the diffusion process of As in Si as well as Si0.9Ge0.1 is obtained. Qualitatively, a higher contribution of vacancies in Si0.9Ge0.1 than in Si is apparent.
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81.05.Cy Elemental semiconductors
61.72.J- Point defects and defect clusters
66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing

Role of microstructure in porous silicon gas sensors for NO2

Zeno Gaburro, Paolo Bettotti, Massimo Saiani, Lorenzo Pavesi, Lucio Pancheri, Claudio J. Oton, and Nestor Capuj

Appl. Phys. Lett. 85, 555 (2004); http://dx.doi.org/10.1063/1.1775887 (3 pages) | Cited 6 times

Online Publication Date: 23 July 2004

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Electrical conductivity of porous silicon fabricated from heavily doped p-type silicon is very sensitive to NO2, even at concentrations below 100 ppb. However, sensitivity depends strongly on the porous microstructure. The structural difference between sensitive and insensitive samples is independently confirmed by microscopy images and by light scattering behavior. A way to change the structure is by modifying the composition of the electrochemical solution. We have found that best results are achieved using ethanoic solutions with HF concentration levels between 12% and 13%.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Cw Elemental semiconductors
61.43.Gt Powders, porous materials

Specific heat and related thermodynamic properties of an undercooled germanium melt

Q. Li, Y. Y. Zhu, R. P. Liu, G. Li, M. Z. Ma, J. K. Yu, J. L. He, Y. J. Tian, and W. K. Wang

Appl. Phys. Lett. 85, 558 (2004); http://dx.doi.org/10.1063/1.1775888 (3 pages) | Cited 5 times

Online Publication Date: 23 July 2004

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Embedded in a flux of dehydrated B2O3, melts of pure germanium were undercooled by repeated melting and solidification of the specimens within a differential scanning calorimeter facility. The highest undercooling obtained in this way was 190 K. The specific heat of the undercooled melt was measured by calorimetric diagnostics within the facility, and showed a linear dependence on temperature. The thermodynamic properties of germanium, such as the difference of Gibbs free energy, the difference of entropy, and the difference of enthalpy between the undercooled melt and the solid state, were derived from the measured specific heat.
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65.40.G- Other thermodynamical quantities
65.40.Ba Heat capacity
64.70.D- Solid-liquid transitions
81.30.Fb Solidification
81.70.Pg Thermal analysis, differential thermal analysis (DTA), differential thermogravimetric analysis

Low-temperature study of nonlinear transport across oxide grain boundaries

Rui Shao, Juro Vavro, and Dawn A. Bonnell

Appl. Phys. Lett. 85, 561 (2004); http://dx.doi.org/10.1063/1.1776329 (3 pages) | Cited 6 times

Online Publication Date: 23 July 2004

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Reduced 36.8° (Σ5) and 24° SrTiO3 bicrystals with carrier concentrations on the order of 1×1017 to 1.0×1018 cm−3 were studied with dc transport measurement from room temperature to 1.4 K. For lightly reduced samples, nonlinearity in I–V curves was observed at very low temperatures indicating the existence of a small grain-boundary potential barrier and the transport mechanism can be rationalized in terms of tunneling through a disordered region associated with the boundary. Samples with further reduction showed no nonlinearity. This reduction-dependent phenomenon is proposed to be due to the oxygen vacancy segregation to the grain boundary.
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73.40.Gk Tunneling
72.80.Jc Other crystalline inorganic semiconductors
61.72.Mm Grain and twin boundaries
61.72.J- Point defects and defect clusters
81.30.Mh Solid-phase precipitation

Nanoscale photothermal and photoacoustic transients probed with extreme ultraviolet radiation

R. I. Tobey, E. H. Gershgoren, M. E. Siemens, M. M. Murnane, H. C. Kapteyn, T. Feurer, and K. A. Nelson

Appl. Phys. Lett. 85, 564 (2004); http://dx.doi.org/10.1063/1.1776332 (3 pages) | Cited 10 times

Online Publication Date: 23 July 2004

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We demonstrate the use of extreme ultraviolet (EUV) light for time-resolved measurements of the photothermal and photoacoustic response of materials. By using wavelengths that are 20× shorter than visible light, we demonstrate the potential for dramatically increased sensitivity and signal levels, in some cases by almost two orders of magnitude compared with visible light. This approach will enable probing of surface acoustic dynamics on nano-scale spatial dimensions of 50 nm and below, using a small scale coherent EUV sources employing high-harmonic generation.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.47.-p Spectroscopy of solid state dynamics

Enhanced photoluminescence of InAs self-assembled quantum dots grown by molecular-beam epitaxy using a “nucleation-augmented” method

C. K. Chia, S. J. Chua, Z. L. Miao, and Y. H. Chye

Appl. Phys. Lett. 85, 567 (2004); http://dx.doi.org/10.1063/1.1773914 (3 pages) | Cited 4 times

Online Publication Date: 23 July 2004

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A two-stage “nucleation-augmented” growth method for producing InAs self-assembled quantum dots (QDs) using molecular-beam epitaxy on GaAs (100) substrates has been investigated in detail. Photoluminescence (PL) measurements show that a 1.8-monolayer-(MLs) InAs QD “nucleation” layer grown at a fast rate, followed by a 2.6-MLs-InAs “augmented” layer grown under pulsed conditions at a slow rate, dramatically increases the dot density and improves the PL intensity for the InAs QDs. It was found that, when the effective growth rate of the InAs augmented layer was reduced, the PL peak emission shifts to a longer wavelength and the PL intensity is enhanced. These changes in characteristics were attributed to improved optical quality and greater dot density.
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78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Aging effects around the glass and melting transitions in poly(dimethylsiloxane) visualized by resistance measurements

H. B. Brom, I. G. Romijn, J. G. Magis, M. van der Vleuten, and M. A. J. Michels

Appl. Phys. Lett. 85, 570 (2004); http://dx.doi.org/10.1063/1.1776334 (3 pages) | Cited 2 times

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The process of aging in rubbers requires monitoring over long periods (days to years). To do so in nonconducting rubbers, small amounts of carbon-black particles were dispersed in a fractal network through the rubber matrix, to make the rubber conducting without modifying its properties. Continuous monitoring of the resistance reveals the structural changes around the glass and melting transitions and especially details about the hysteresis and aging processes. We illustrate the method for the semicrystalline polymer poly(dimethylsiloxane).
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.70.D- Solid-liquid transitions
72.80.Tm Composite materials

Electric current enhanced defect mobility in Ni3Ti intermetallics

Javier E. Garay, Stephen C. Glade, Umberto Anselmi-Tamburini, Palakkal Asoka-Kumar, and Zuhair A. Munir

Appl. Phys. Lett. 85, 573 (2004); http://dx.doi.org/10.1063/1.1774268 (3 pages) | Cited 61 times

Online Publication Date: 23 July 2004

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The effect of the application of a dc current on the annealing of point defects in Ni3Ti was investigated by positron annihilation spectroscopy. An increased defect annealing rate was observed under the influence of the current and was attributed to a 24% decrease in the activation energy of mobility. The results are interpreted in terms of the electron wind effect and the complex nature of diffusion in ordered intermetallic phases. They provide direct evidence for an increase in defect mobility in ordered intermetallics under the influence of a current.
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61.72.J- Point defects and defect clusters
66.30.Lw Diffusion of other defects
81.40.Gh Other heat and thermomechanical treatments
78.70.Bj Positron annihilation

Effect of Cu deficiency on the optical properties and electronic structure of CuInSe2 and CuIn0.8Ga0.2Se2 determined by spectroscopic ellipsometry

Sung-Ho Han, Allen M. Hermann, F. S. Hasoon, H. A. Al-Thani, and D. H. Levi

Appl. Phys. Lett. 85, 576 (2004); http://dx.doi.org/10.1063/1.1776616 (3 pages) | Cited 16 times

Online Publication Date: 23 July 2004

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Spectroscopic ellipsometry measurements of CuInSe2 (CIS) and CuIn0.8Ga0.2Se2 (CIGS) reveal that there are important differences in electronic properties between stoichiometric CIS (CIGS) and Cu-poor CIS (CIGS). We find a reduction in the absorption strength in the spectral region of 1–3 eV. This reduction can be explained in terms of the Cu 3d density of states. Cu-poor CIS (CIGS) materials show an increase in band gap due to the reduction in repulsion between Cu 3d and Se 4p states. The experimental results have important implications for the function of polycrystalline optoelectronic devices.
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71.20.Nr Semiconductor compounds
78.66.Li Other semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology

Diffusion barrier properties of carboxyl- and amine-terminated molecular nanolayers

P. G. Ganesan, A. P. Singh, and G. Ramanath

Appl. Phys. Lett. 85, 579 (2004); http://dx.doi.org/10.1063/1.1775035 (3 pages) | Cited 23 times

Online Publication Date: 23 July 2004

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Molecular nanolayers are attractive for preserving the integrity of Cu-dielectric interface in sub-50 nm interconnect structures. Here, we demonstrate the use of carboxyl- and amine-terminated self-assembled molecular layers (SAMs) to immobilize Cu at the Cu∕SiO2 interface. Amine-terminated SAMs at the Cu∕SiO2 interface increase the Cu diffusion-induced device failure time by a factor of 3 compared to interfaces without a barrier. Carboxyl-terminated SAMs obtained by grafting succinyl chloride onto the amine-terminated SAM show more than an additional factor of 4 increase in failure time. Coordination complex formation though strong interactions between COOH and Cu+ at the Cu∕SAM interface is the likely reason for the effective immobilization of Cu.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Nitrogen self-diffusion in silicon nitride thin films probed with isotope heterostructures

H. Schmidt, G. Borchardt, M. Rudolphi, H. Baumann, and M. Bruns

Appl. Phys. Lett. 85, 582 (2004); http://dx.doi.org/10.1063/1.1769594 (3 pages) | Cited 3 times

Online Publication Date: 23 July 2004

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The self-diffusion of nitrogen is measured with secondary ion mass spectrometry in isotopically enriched polycrystalline and amorphous Si314N4∕Si315N4∕Si314N4 isotope heterostructures which were produced by reactive magnetron sputtering. The N diffusivities of polycrystalline films in the temperature range between 1130 and 1700 °C follow an Arrhenius law over four orders of magnitude with a single activation enthalpy of ΔH=4.9 eV and a pre-exponential factor of D0=1×10−6 m2∕s. The calculated entropy of diffusion of ΔS≈0 kB indicates a diffusion mechanism with localized point defects, in contrast to extended point defects usually found in semiconductors, like Si, Ge, and GaAs. The diffusivities in the amorphous state between 1130 and 1180 °C do not differ significantly from those in the polycrystalline state.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
81.15.Cd Deposition by sputtering
65.40.G- Other thermodynamical quantities
68.60.Wm Other nonelectronic physical properties
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
61.72.Nn Stacking faults and other planar or extended defects
66.30.H- Self-diffusion and ionic conduction in nonmetals
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Oxygen as a surfactant for Al contact metallization of organic layers

J. Ivanco, B. Winter, F. P. Netzer, M. G. Ramsey, L. Gregoratti, and M. Kiskinova

Appl. Phys. Lett. 85, 585 (2004); http://dx.doi.org/10.1063/1.1775284 (3 pages) | Cited 8 times

Online Publication Date: 23 July 2004

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Show Abstract
Valence band and spatially resolved x-ray photoemission studies of the Al growth on sexiphenyl films, in both an ultrahigh vacuum (UHV) and in a partial pressure of oxygen, are reported. We show that in an UHV, even for very high coverages, the Al balls up on the organic film and is discontinuous. In contrast, for growth in an oxygen partial pressure, similar to that in standard high-vacuum systems used in organic device production, very thin continuous conducting wetting layers are formed. We suggest that the oxygen acts like a surfactant that allows the high surface free-energy metal to wet low surface free-energy organic films.
Show PACS
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)
85.40.Ls Metallization, contacts, interconnects; device isolation
65.40.G- Other thermodynamical quantities
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.-a Thin film structure and morphology
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.08.Bc Wetting
68.35.Md Surface thermodynamics, surface energies
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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