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7 Feb 2000

Volume 76, Issue 6, pp. 661-788

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High-efficiency organic polymer light-emitting heterostructure devices on flexible plastic substrates

Yi He and Jerzy Kanicki

Appl. Phys. Lett. 76, 661 (2000); http://dx.doi.org/10.1063/1.125854 (3 pages) | Cited 42 times

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In this letter, we describe a high-efficiency organic polymer light-emitting heterostructure device with aluminum cathode fabricated on a thin, flexible plastic substrate. The device consists of a hole transporting (amine-fluorene) and an emissive (benzothiadiazole-fluorene) conjugated organic polymer layers. The best heterostructure device has a green light emission and a maximum luminance higher than 2000 cd/m2. Device shows a maximum emission of ∼56.2 cd/A and, accordingly, a maximum luminous and external quantum efficiency of ∼9.0 lm/W and ∼ 15%, respectively. This organic light-emitting diode performance is acceptable for flat panel display applications. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems

Photocurrent in an electron transporting luminescent polymer

F. Feller and A. P. Monkman

Appl. Phys. Lett. 76, 664 (2000); http://dx.doi.org/10.1063/1.125855 (3 pages) | Cited 8 times

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Photocurrent measurements have been carried out on thin films of poly(2,5-pyridinediyl), a promising polymer for applications in light-emitting diodes. The spectral dependence of the photocurrent has been recorded using the four possible directions of the applied electric field and illumination, and clear symbatic and antibatic behavior was observed. A strong, symmetric photocurrent increase with bias has been found, while the temperature dependence is relatively weak. The analysis of the results provides evidence that electrons are the majority charge carriers and gives insight into the carrier-transport mechanism in poly(2,5-pyridinediyl). © 2000 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Patterning 100 nm features using deep-ultraviolet contact photolithography

James G. Goodberlet

Appl. Phys. Lett. 76, 667 (2000); http://dx.doi.org/10.1063/1.125856 (3 pages) | Cited 35 times

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The extension of contact photolithography to pattern features at the 100 nm level, and below, is described. Isolated lines, nested L’s, and gratings with 100 nm linewidths are patterned using a conformable embedded-amplitude mask, a trilayer resist stack on the substrate, and a deep-ultraviolet radiation source having a wavelength of λ ∼ 220 nm. A broad exposure latitude of ±21% for a linewidth control of ±10% is measured. Preliminary calculations indicate a practical resolution limit for the lithographic process. The patterning process is reliable and repeatable. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer

Direct observation of the Gouy phase shift in THz impulse ranging

R. W. McGowan, R. A. Cheville, and D. Grischkowsky

Appl. Phys. Lett. 76, 670 (2000); http://dx.doi.org/10.1063/1.125857 (3 pages) | Cited 19 times

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Here we present a direct observation of the Gouy effect through THz impulse scattering from cylindrical and spherical targets. A π/2 Gouy phase shift through a one-axis focus compared to the more common π phase shift of the two-axis focus is required to interpret the scattering results using a physical optics model. © 2000 American Institute of Physics.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.Xb Telemetry: remote control, remote sensing; radar

Fabrication of circular optical structures with a 20 nm minimum feature size using nanoimprint lithography

Mingtao Li, Jian Wang, Lei Zhuang, and Stephen Y. Chou

Appl. Phys. Lett. 76, 673 (2000); http://dx.doi.org/10.1063/1.125896 (3 pages) | Cited 37 times

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We demonstrated the fabrication of Fresnel zone plates with a 75 nm minimum feature size and circular gratings with a 20 nm minimum linewidth in polymethyl methacrylate using nanoimprint lithography, and in metals by means of a lift-off technique. Observation of sharp Moiré patterns indicated the high fidelity of nanoimprint lithography in pattern duplication. Our results showed that nanoimprint lithography is a promising technology for patterning integrated optics. © 2000 American Institute of Physics.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings
42.30.Ms Speckle and moiré patterns
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Direct identification of the synergism between methyl radicals and atomic hydrogen during growth of amorphous hydrogenated carbon films

A. von Keudell, T. Schwarz-Selinger, M. Meier, and W. Jacob

Appl. Phys. Lett. 76, 676 (2000); http://dx.doi.org/10.1063/1.125858 (3 pages) | Cited 40 times

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The simultaneous interaction of methyl radicals (CH3) and atomic hydrogen (H) with the surface of amorphous hydrogenated carbon (a-C:H) film is investigated. Two identical quantified beam sources for H and CH3 are used. The growth and/or erosion during the simultaneous interaction of the two beams with an amorphous hydrogenated carbon film is monitored by using in situ real-time ellipsometry at a substrate temperature of 320 K. Interaction with the CH3 beam alone causes slow growth, corresponding to a sticking coefficient for CH3 of ∼ 3×10−5. Simultaneous interaction of the atomic hydrogen beam and the CH3 radical beam yields a sticking coefficient for CH3 of 3×10−3, which is two orders of magnitude larger than for CH3 alone. From a microscopic modeling of this synergistic growth, the reaction probability for CH3 adsorbing at an adsorption site, which is created by atomic hydrogen at the surface, is derived to be 0.14. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.05.Gc Amorphous semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.66.Jg Amorphous semiconductors; glasses
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Effect of carrier confinement on photoluminescence from modulation-doped AlxGa1−xN/GaN heterostructures

B. Shen, T. Someya, O. Moriwaki, and Y. Arakawa

Appl. Phys. Lett. 76, 679 (2000); http://dx.doi.org/10.1063/1.125859 (3 pages) | Cited 16 times

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Photoluminescence (PL) of modulation-doped Al0.22Ga0.78N/GaN heterostructures was investigated. The PL peak related to recombination between the two-dimensional electron gases (2DEG) and photoexcited holes is located at 3.448 eV at 40 K, which is 45 meV below the free excitons (FE) emission in GaN. The peak can be observed at temperatures as high as 80 K. The intensity of the 2DEG PL peak is enhanced significantly by incorporating a thin Al0.12Ga0.88N layer into the GaN layer near the heterointerface to suppress the diffusion of photoexcited holes. The energy separation of the 2DEG peak and the GaN FE emission decreases with increasing temperature. Meanwhile, the 2DEG peak energy increases with increasing excitation intensity. These results are attributed to the screening effect of electrons on the bending of the conduction band at the heterointerface, which becomes stronger when temperature or excitation intensity is increased. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Ge–Si intermixing in Ge quantum dots on Si(001) and Si(111)

F. Boscherini, G. Capellini, L. Di Gaspare, F. Rosei, N. Motta, and S. Mobilio

Appl. Phys. Lett. 76, 682 (2000); http://dx.doi.org/10.1063/1.125860 (3 pages) | Cited 75 times

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Exploiting Ge K-edge x-ray absorption spectroscopy we provide direct evidence of Si–Ge intermixing in self-organized strained and unstrained Ge quantum dots on Si, and provide a quantitative measurement of the average composition. For Ge/Si(001) dots with equivalent thickness in the range 5.8–38 nm and morphology ranging from that typical of coherently strained to that associated with relaxed dots we find that the average Si composition is approximately 30%. For Ge/Si(111), we find that the wetting layer has a Si composition near 50%. We discuss these results in terms of the energetics of dot formation and argue that strain-enhanced diffusion of Si into Ge should be considered as an important factor in minimizing the strain energy of the system. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
78.70.Dm X-ray absorption spectra

Coexistence of planar and three-dimensional quantum dots in CdSe/ZnSe structures

M. Strassburg, Th. Deniozou, A. Hoffmann, R. Heitz, U. W. Pohl, D. Bimberg, D. Litvinov, A. Rosenauer, D. Gerthsen, S. Schwedhelm, K. Lischka, and D. Schikora

Appl. Phys. Lett. 76, 685 (2000); http://dx.doi.org/10.1063/1.125861 (3 pages) | Cited 40 times

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Two well distinguishable classes of nanoscale islands were identified in CdSe/ZnSe quantum dot structures by optical spectroscopy and transmission electron microscopy. For 2.1 to 3.1 monolayer CdSe deposition, coherent three-dimensional (3D) islands, formed in the Stranski–Krastanow (SK) mode, are found with typical diameters of ∼16 nm and a coverage-dependent density of up to 3×1010 cm−2. Simultaneously, small islands with lateral extensions below 10 nm and a density of ∼ 5×1011 cm−2 are formed by strain-modified island growth. Whereas the 3D SK islands dominate the emission properties at room temperature, the latter smaller islands determine the optical properties at temperatures below 120 K. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors

Indirect excitation of 1.5 μm emission from Er3+ in silicon-rich silica

A. J. Kenyon, C. E. Chryssou, and C. W. Pitt

Appl. Phys. Lett. 76, 688 (2000); http://dx.doi.org/10.1063/1.125862 (3 pages) | Cited 9 times

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We report the observation of near-IR emission from erbium in silicon-rich silica, excited using a filtered white-light source. The characteristic 4I13/2–4I15/2 intra-4f transition at 1535 nm is observed even when excitation wavelengths corresponding to the principal erbium optical absorption bands are removed using selective filtering. We ascribe this effect to an efficient transfer mechanism between silicon nanoclusters present in the silicon-rich silica films and the rare-earth ions. This is in good agreement with our previous work in this area and suggests the possibility of obtaining flashlamp-pumped erbium optoelectronic devices. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators

Tuning the energy levels of self-assembled InAs quantum dots by rapid thermal annealing

T. M. Hsu, Y. S. Lan, W.-H. Chang, N. T. Yeh, and J.-I. Chyi

Appl. Phys. Lett. 76, 691 (2000); http://dx.doi.org/10.1063/1.125863 (3 pages) | Cited 39 times

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We studied the photoluminescence spectra of rapid-thermal-annealed self-assembled InAs quantum dots at 10 K. For annealing temperatures ranging from 700 to 950 °C, we observed a blueshift in the interband transition energies, a decrease in the intersublevel spacing energies, and a narrowing of photoluminescence linewidths. In this letter, we demonstrate that the tuning of the InAs quantum dots interband transition and intersublevel spacing energies can be achieved by 30 s of rapid thermal annealing. The relation between interband transition energy changes and the intersublevel spacing energies is found to be linear, with a slope close to the ratio of the dots’ height to their diameter. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Neutron diffraction study of the reduction of NiAl2O4

E. Ustundag, B. Clausen, and M. A. M. Bourke

Appl. Phys. Lett. 76, 694 (2000); http://dx.doi.org/10.1063/1.125864 (3 pages) | Cited 4 times

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The reduction of a solid NiAl2O4 cylinder to a metal-ceramic composite consisting of Ni particles in an Al2O3 matrix was monitored in situ at 1220 °C with neutron powder diffraction. The reaction kinetics was determined with a time resolution of 30 min. The reduction is associated with a volume shrinkage. A comparison of finite element calculations and the changes in the measured lattice parameters suggests that creep has relaxed the residual strains that would otherwise result from the volume shrinkage. The data also indicate that structural evolution in unreduced NiAl2O4 via a change in the cationic sublattice towards inverse spinel occurred and that led to a variation in lattice parameters. © 2000 American Institute of Physics.
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82.30.-b Specific chemical reactions; reaction mechanisms
61.66.Fn Inorganic compounds
81.40.Lm Deformation, plasticity, and creep
62.20.Hg Creep

Cross-sectional electron-beam-induced current analysis of the passivation of extended defects in cast multicrystalline silicon by remote hydrogen plasma treatment

O. F. Vyvenko, O. Krüger, and M. Kittler

Appl. Phys. Lett. 76, 697 (2000); http://dx.doi.org/10.1063/1.125865 (3 pages) | Cited 11 times

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Cross-sectional and temperature-dependent measurements of the electron-beam-induced current reveal the depth profile of the recombination activity of grain boundaries and intragrain dislocations in cast multicrystalline Si. After remote hydrogen plasma treatment for 1 h at 310 °C, defects are passivated down to a depth of 100 μm. Even the activity of crystal defects exhibiting small or not detectable room temperature contrast is further reduced by hydrogenation. We interpret the experimental data in terms of a recently developed model, which relates the temperature behavior of the recombination activity to the density of (contaminant-induced) deep levels at the defects. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
61.72.Nn Stacking faults and other planar or extended defects
81.65.Rv Passivation
73.25.+i Surface conductivity and carrier phenomena
72.80.Cw Elemental semiconductors
61.72.Mm Grain and twin boundaries
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Cross-sectional nanophotoluminescence studies of Stark effects in self-assembled quantum dots

H. Htoon, J. W. Keto, O. Baklenov, A. L. Holmes, and C. K. Shih

Appl. Phys. Lett. 76, 700 (2000); http://dx.doi.org/10.1063/1.125866 (3 pages) | Cited 17 times

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By using a cross-sectional geometry, we show the capability to perform single-dot spectroscopy in self-assembled quantum dots using far-field optics. By using this method, we study the quantum-confined Stark effect in self-assembled quantum dots. For single-stack quantum dots (QDs), we find that the spectra are redshifted with an increase in electric field. For vertically coupled double-stack quantum dots, while most of the QDs are redshifted, some QDs show blueshifted spectra, which can be interpreted as an evidence of coupled QD molecules. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Relaxation of an epitaxial InGaAs film on a thin twist-bonded (100) GaAs substrate

St. Senz, G. Kästner, U. Gösele, and V. Gottschalch

Appl. Phys. Lett. 76, 703 (2000); http://dx.doi.org/10.1063/1.125867 (3 pages) | Cited 7 times

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A 30 nm (100) GaAs layer was transferred by twist wafer bonding to a (100) GaAs handling wafer. A similar structure was proposed in the literature as a “compliant substrate.” Transmission electron microscopy and x-ray diffraction of 40 and 300 nm epitaxial InGaAs films (0.5% misfit) showed no evidence of a relaxation mechanism specifically attributed to a compliant substrate. The 40 nm film was nearly pseudomorphic without any evidence of a relaxation mechanism, like grain-boundary sliding. The possibility of grain-boundary slip along the twist-bonded interface is discussed. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Selective nucleation and growth of carbon nanotubes at the CoSi2/Si interface

L. P. Biró, G. Molnár, I. Szabó, Z. Vértesy, Z. E. Horváth, J. Gyulai, Z. Kónya, P. Piedigrosso, A. Fonseca, J. B. Nagy, and P. A. Thiry

Appl. Phys. Lett. 76, 706 (2000); http://dx.doi.org/10.1063/1.125868 (3 pages) | Cited 7 times

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A patterned CoSi2/Si substrate was used for the catalytic growth of carbon nanostructures and nanotubes in the temperature range of 750–800 °C, using acetylene/N2 as a reaction mixture flowing through a quartz tube at ambient pressure. Selective nucleation confined to the CoSi2/Si interface region was achieved. Scanning electron microscopy and transmission electron microscopy were used to investigate the grown nanostructures. © 2000 American Institute of Physics.
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81.05.ub Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Sequential ion-induced stress relaxation and growth: A way to prepare stress-relieved thick films of cubic boron nitride

H.-G. Boyen, P. Widmayer, D. Schwertberger, N. Deyneka, and P. Ziemann

Appl. Phys. Lett. 76, 709 (2000); http://dx.doi.org/10.1063/1.125869 (3 pages) | Cited 45 times

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It is shown that the bombardment of high quality cubic (c-) BN films with 300 keV Ar+ ions leads to a strong relaxation of their compressive stresses without destroying the cubic phase if the total ion fluence is kept below an upper limit. In addition, it was found that on top of such a stress-relieved film a further pure c-BN layer can be grown, but it builds up compressive stress again. Based on both results, a procedure is developed to grow thick (>1 μm) c-BN films (>80% c-BN) exhibiting low residual stress and long term stability under ambient conditions. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Hardening of fullerite C60 during temperature-induced polymerization and amorphization under pressure

A. G. Lyapin, V. V. Brazhkin, E. L. Gromnitskaya, S. V. Popova, O. V. Stal’gorova, R. N. Voloshin, S. C. Bayliss, and A. V. Sapelkin

Appl. Phys. Lett. 76, 712 (2000); http://dx.doi.org/10.1063/1.125870 (3 pages) | Cited 25 times

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We report a detailed study of Vicker’s hardness and ultrasonic elastic moduli for carbon phases prepared by heating fullerite C60 at pressures of 3.5, 5, and 8 GPa. It is shown that the transformation of two-dimensional C60 polymers into graphite-like amorphous carbon is accompanied by an increase in hardness of 100–200 times, as well as an increase in bulk and shear moduli by 4–5 and 2–3 times, respectively, with no density jump taking place. It is proposed that the high hardness (up to 40 GPa) of the disordered phases synthesized is caused by the three-dimensional ordering of sp2-based network. It was found that, in the 3.5–8 GPa interval, the mechanical properties of the phases obtained depend basically on the temperature rather than on the pressure of synthesis. © 2000 American Institute of Physics.
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62.20.Qp Friction, tribology, and hardness
82.35.-x Polymers: properties; reactions; polymerization
61.43.-j Disordered solids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.50.-p High-pressure effects in solids and liquids
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Room-temperature silicidation using radiation-enhanced diffusion in hydrogenated amorphous silicon

J. M. Shannon, M. K. Chai, and B. J. Sealy

Appl. Phys. Lett. 76, 715 (2000); http://dx.doi.org/10.1063/1.125871 (3 pages) | Cited 1 time

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Amorphous disilicides of the refractory metals chromium and molybdenum have been formed at room temperature in hydrogenated amorphous silicon. The silicides are produced by radiation-enhanced diffusion during bombardment through a thin metal film on the surface of the amorphous silicon. The properties of the layers are similar to those produced by thermal annealing at temperatures <300 °C. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
61.82.Fk Semiconductors

Mg doping of GaN layers grown by plasma-assisted molecular-beam epitaxy

I. P. Smorchkova, E. Haus, B. Heying, P. Kozodoy, P. Fini, J. P. Ibbetson, S. Keller, S. P. DenBaars, J. S. Speck, and U. K. Mishra

Appl. Phys. Lett. 76, 718 (2000); http://dx.doi.org/10.1063/1.125872 (3 pages) | Cited 40 times

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GaN:Mg layers grown by plasma-assisted molecular-beam epitaxy at 650 °C are investigated. Secondary-ion-mass-spectroscopy measurements reveal uniform Mg doping profiles with very sharp boundaries. The amount of incorporated Mg atoms changes approximately linearly with incident Mg flux. Hall measurements on p-type GaN:Mg layers show that about 1%–2% of all Mg atoms are ionized at room temperature. The hole mobility depends strongly on the hole concentration, varying from μp = 24 cm2/V s for p = 1.8×1017 cm−3 to μp = 7.5 cm2/V s for p = 1.4×1018 cm−3. GaN p–n diodes with molecular-beam-epitaxy-grown p regions are analyzed using current–voltage measurements. © 2000 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance
85.30.Kk Junction diodes
81.05.Ea III-V semiconductors

Spontaneous formation of complex and ordered structures on oxygen-plasma-treated elastomeric polydimethylsiloxane

Diana B. H. Chua, H. T. Ng, and Sam F. Y. Li

Appl. Phys. Lett. 76, 721 (2000); http://dx.doi.org/10.1063/1.125873 (3 pages) | Cited 53 times

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In this letter, we describe the spontaneous formation of complex and ordered structures on polydimethylsiloxane when subjected to oxygen plasma treatment. Periodicity of wavy structures from submicrometer to micrometer length scales could be generated reproducibly and quantitatively accounted for. The origin of these patterns could be related to the relief of compressive stress by buckling of the silica-like thin film that was formed as a result of the plasma exposures. Atomic force microscope has been used to characterize the varied trends of the modifications. The present approach could be extended to the fabrication of intricate ordered patterns on polymeric surfaces with integrated relief structures obtained by soft lithography and micromolding. © 2000 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Smoothening of Cu films grown on Si(001)

R. A. Lukaszew, Y. Sheng, C. Uher, and R. Clarke

Appl. Phys. Lett. 76, 724 (2000); http://dx.doi.org/10.1063/1.125874 (3 pages) | Cited 10 times

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We report an in situ study of the molecular-beam epitaxy growth and annealing of Cu(001) films grown on hydrogen-terminated Si(001) substrates, resulting in a promising approach to achieve smooth epitaxial morphology. Using correlated reflection high-energy electron diffraction and scanning tunneling microscopy data, we find a temperature interval below the onset of silicide formation where a dramatic smoothening of the epitaxial Cu surfaces occurs. Our measurements indicate that a reduction in roughness is possible in this regime because the annealing is controlled by lateral diffusion kinetics. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Interface structure of ultrathin CoSi2 films epitaxially grown on Si(111)

A. Seubert, J. Schardt, W. Weiß, U. Starke, K. Heinz, and Th. Fauster

Appl. Phys. Lett. 76, 727 (2000); http://dx.doi.org/10.1063/1.125875 (3 pages) | Cited 10 times

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The interface structure of ultrathin CoSi2 films grown on Si(111) was investigated by quantitative low-energy electron diffraction. Codeposition of the elements leads to a film composed of domains with two and three Si–Co–Si trilayers in CaF2 structure. As within the film, Co atoms at the interface are eightfold coordinated. The lateral unit cells of the film and substrate are mutually rotated by 60° (B-type orientation). The interfacial trilayer is substantially distorted, its distance to the substrate expanded, and its sublayer spacings considerably modified from the bulk. Also, the substrate’s top spacing is expanded. The results compare almost quantitatively with recent density-functional calculations. © 2000 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
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Surface and bulk passivation of GaAs solar cell on Si substrate by H2+PH3 plasma

G. Wang, T. Ogawa, M. Umeno, T. Soga, and T. Jimbo

Appl. Phys. Lett. 76, 730 (2000); http://dx.doi.org/10.1063/1.125876 (3 pages) | Cited 3 times

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A promising passivation method for GaAs solar cell grown on Si substrate (GaAs/Si solar cell) by phosphine-added hydrogen (PH3/H2) plasma exposure has been envisaged. The defect-hydrogenation and the surface-phosphidization effects of GaAs/Si solar cell are realized simultaneously by this single passivation process. Consequently, surface recombination states are reduced and the minority carrier lifetime is increased, resulting in a significant reduction in saturation current density (J0) of the GaAs/Si p–n junction. High open-circuit voltage (0.93 V) and fill factor (80.9%) are obtained for the PH3 plasma exposed GaAs/Si solar cells. As a result, the conversion efficiency is increased from 15.9% to 18.6%. This approach provides a simple and effective method to improve the photovoltaic properties of GaAs/Si solar cell. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
81.05.Ea III-V semiconductors
81.65.Rv Passivation
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena

Isolation of a metallic Si(111)7×7 surface reconstruction via separation by implanted oxygen

M. Noh, G. E. Jellison, F. Namavar, and H. H. Weitering

Appl. Phys. Lett. 76, 733 (2000); http://dx.doi.org/10.1063/1.125877 (3 pages) | Cited 4 times

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High-quality Si(111)7×7 surface reconstructions have been observed on (111)-oriented Si/SiO2/Si substrates, prepared via separation by implantation of oxygen, or “SIMOX,” with top layer thicknesses as small as 220 Å. Scanning tunneling microscopy and spectroscopy data indicate that the electrically and physically isolated top layer is electrically conducting, in contrast to that of (100) SIMOX material, which accumulates charge under typical imaging conditions. We speculate that the 7×7 reconstruction on (111) SIMOX material is an efficient conduction channel, allowing atomic resolution imaging of the isolated Si top layer. © 2000 American Institute of Physics.
Show PACS
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
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