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28 Feb 2005

Volume 86, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 86, 093101 (2005); http://dx.doi.org/10.1063/1.1870108 (3 pages)

G. S. Paraoanu and A. M. Halvari
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Interaction of atomic hydrogen with Zn-polar and O-polar ZnO surfaces

Maria Losurdo and Maria M. Giangregorio

Appl. Phys. Lett. 86, 091901 (2005); http://dx.doi.org/10.1063/1.1870103 (3 pages) | Cited 13 times

Online Publication Date: 23 February 2005

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The interaction of Zn-polar and O-polar ZnO surfaces with atomic hydrogen produced by a remote rf plasma source is investigated in situ and in real time using spectroscopic ellipsometry. It is found that the reactivity of ZnO with atomic hydrogen depends on polarity. The interaction of O-polar surfaces with atomic hydrogen at 100 °C is suitable for producing clean surfaces, while Zn-polar surfaces strongly react with atomic hydrogen resulting in a disruption of the ZnO lattice with formation of Zn surface clusters.
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68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Yellowish-white luminescence in codoped zinc oxide

Naoki Ohashi, Naoki Ebisawa, Takashi Sekiguchi, Isao Sakaguchi, Yoshiki Wada, Tadashi Takenaka, and Hajime Haneda

Appl. Phys. Lett. 86, 091902 (2005); http://dx.doi.org/10.1063/1.1871349 (3 pages) | Cited 23 times

Online Publication Date: 23 February 2005

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The broad-band visible emission of codoped ZnO was studied. The codoped ZnO specimens were intentionally and simultaneously doped with IIIa elements (donors) and Li (acceptor). Broad-band emission covering nearly the whole visible range was achieved. The emission was found to be yellowish white to the naked eye. The visible band was composed of two components, i.e., a green emission having a peak at 2.2 eV and a yellow emission having a peak at 2.0 eV. The peak at 2.2 eV was distinct from the nonstructured green emission at 2.45 eV. The 2.2 and 2.0 eV peaks were attributed to donor-acceptor pair transitions involving the zinc vacancy and lithium, respectively.
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78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.S- Impurities in crystals
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters

Observation of recombination enhanced defect annealing in 4H–SiC

L. Storasta, F. H. C. Carlsson, J. P. Bergman, and E. Janzén

Appl. Phys. Lett. 86, 091903 (2005); http://dx.doi.org/10.1063/1.1811381 (3 pages) | Cited 5 times

Online Publication Date: 23 February 2005

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We report observation of recombination enhanced defect annealing in 4H–SiC detected by capacitance transient spectroscopy and low temperature photoluminescence (PL). Intrinsic defect centers, created by 160 keV electron irradiation, reduce in concentration after illumination at temperatures much lower than previously reported annealing temperatures of 400 and 800 °C. The effect is observed after both external intense above band gap laser excitation, and with recombination in a forward biased pin diode. PL measurements show that several lines, normally detected after electron irradiation, have almost or entirely disappeared by recombination enhanced annealing at room temperature. From capacitance transient measurements, the annealing enhancement is found to be largest for the HS2 hole trap, while the EH1 and EH3 electron traps also anneal out by recombination enhanced reaction but at a lower rate.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.55.Hx Other solid inorganic materials
61.72.Cc Kinetics of defect formation and annealing
61.80.Fe Electron and positron radiation effects

Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition

B. N. Mbenkum, N. Ashkenov, M. Schubert, M. Lorenz, H. Hochmuth, D. Michel, M. Grundmann, and G. Wagner

Appl. Phys. Lett. 86, 091904 (2005); http://dx.doi.org/10.1063/1.1862778 (3 pages) | Cited 26 times

Online Publication Date: 24 February 2005

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Temperature-dependent dielectric and electro-optic properties of a ZnO-BaTiO3-ZnO heterostructure grown by pulsed-laser deposition on (0001) sapphire are reported. The wurtzite-structure ZnO layers serve as transparent conducting electrodes. Previously observed coupling effects within the wurtzite-perovskite heterostructure by spectroscopic electro-optic ellipsometry birefringence measurements manifest themselves as a “pinning” of the ferroelectric polarization in the BaTiO3 layer by the cladding ZnO layers. Temperature-controlled electro-optic Raman measurements assign the electro-optic birefringence results to a temperature-driven phase transition resulting from the leakage current within the sample. High-temperature small-signal capacitance measurements exploiting the conductive electrode properties of the cladding layers reveal occurrence of the Curie temperature of the BaTiO3 layer at 384 K.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
78.20.Jq Electro-optical effects
78.66.Nk Insulators
78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
78.20.Fm Birefringence
78.30.Hv Other nonmetallic inorganics
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization

Temperature dependence of the tangential momentum accommodation coefficient for gases

Bing-Yang Cao, Min Chen, and Zeng-Yuan Guo

Appl. Phys. Lett. 86, 091905 (2005); http://dx.doi.org/10.1063/1.1871363 (3 pages) | Cited 25 times

Online Publication Date: 24 February 2005

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The temperature dependence of the tangential momentum accommodation coefficient (TMAC) is investigated by examining gas flows in a submicron channel using molecular dynamics simulations. The results show that the TMAC decreases with the increasing temperature following an exponential decay law, and is more sensitive to lower temperatures than to higher ones. The molecular trapping-desorption behaviors near the channel surface are found to be responsible for this dependence.
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47.45.Gx Slip flows and accommodation
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.15.-x Laminar flows
47.10.-g General theory in fluid dynamics

Electron-lattice coupling in ZnFe2O4/TiO2 nanocomposite films

Yunxia Jin, Guanghai Li, and Lide Zhang

Appl. Phys. Lett. 86, 091906 (2005); http://dx.doi.org/10.1063/1.1866503 (3 pages) | Cited 1 time

Online Publication Date: 24 February 2005

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Electron-lattice (e-ph) coupling originated from the low-temperature photoluminescence in ZnFe2O4/TiO2 nanocomposite films has been studied. The purely linear character of the e-ph coupling is shown through the Huang–Rhys model within the Franck–Condon approximation. The interfacial coupling capability between the ZnFe2O4 nanoparticles and the TiO2 host lattice is characterized by the Huang–Rhys factors (S0) and the vibrational quantum energy (ℏΩ). It is found that the Huang–Rhys factors S0 increases with increasing the content of ZnFe2O4 in the TiO2 films and the vibrational energy ℏΩ is quite in agreement with that in the infrared spectra.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Ductile titanium-based glassy alloy ingots

Faqiang Guo, Hsiang-Jen Wang, S. Joseph Poon, and Gary J. Shiflet

Appl. Phys. Lett. 86, 091907 (2005); http://dx.doi.org/10.1063/1.1872214 (3 pages) | Cited 72 times

Online Publication Date: 24 February 2005

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We report that ductile and strong amorphous titanium metallic alloys ( ∼ twice the strength of high-strength titanium alloys) have been discovered that are in the form of glassy ingots. It is found that the suppression of a competing stable quasicrystalline phase upon solidification is particularly important in forming the current glassy ingots. While there is significant technological potential for these titanium alloys, the present findings have important implications on the design of highly processable bulk metallic glasses.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
64.70.D- Solid-liquid transitions
81.30.Fb Solidification
61.43.Fs Glasses
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

Photoluminescence of silicon quantum dots in silicon nitride grown by NH3 and SiH4

Baek-Hyun Kim, Chang-Hee Cho, Tae-Wook Kim, Nae-Man Park, Gun Yong Sung, and Seong-Ju Park

Appl. Phys. Lett. 86, 091908 (2005); http://dx.doi.org/10.1063/1.1872211 (3 pages) | Cited 43 times

Online Publication Date: 25 February 2005

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The photoluminescence (PL) property of crystalline silicon quantum dots (Si QDs) in silicon nitride grown by using ammonia and silane gases is reported. The peak position of PL could be controlled in the wavelength range from 450 to 700 nm by adjusting the flow rates of ammonia and silane gases. The PL intensity of Si QDs grown by ammonia was more intense compared to that of Si QDs grown by nitrogen gas. To investigate the role of hydrogen in the PL enhancement, the Si QDs grown by nitrogen gas were postannealed under hydrogen ambient. The enhancement in PL intensity was attributed to the hydrogen passivation of dangling bonds related to silicon and/or nitrogen at the interface of Si QDs and silicon nitride.
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81.05.Cy Elemental semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
71.55.Cn Elemental semiconductors
81.65.Rv Passivation
68.55.-a Thin film structure and morphology
68.65.Hb Quantum dots (patterned in quantum wells)
61.72.Cc Kinetics of defect formation and annealing
78.55.Ap Elemental semiconductors

Reconciliation of luminescence and Hall measurements on the ternary semiconductor CuGaSe2

Susanne Siebentritt, Inge Beckers, Till Riemann, Jürgen Christen, Axel Hoffmann, and Matthias Dworzak

Appl. Phys. Lett. 86, 091909 (2005); http://dx.doi.org/10.1063/1.1872215 (3 pages) | Cited 10 times

Online Publication Date: 25 February 2005

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Previous Hall and photoluminescence investigations on CuGaSe2 yielded conflicting results: defect depths determined by luminescence are lower than the ionization energy found in electrical measurements. In this contribution, we present time and spatially resolved cathodoluminescence measurements that necessitate a new interpretation of the luminescence data, leading to a consistent model for luminescence and Hall data with three acceptors with ionization energies of 60, 100, and 150 meV. Luminescence decay times are long, in the range of 100 ns, indicating strong capture. Luminescence is spatially inhomogeneous, indicating inhomogeneous distribution of defects.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Ht Other nonmetals
84.60.Jt Photoelectric conversion

Achieving fast oxygen diffusion in perovskites by cation ordering

A. A. Taskin, A. N. Lavrov, and Yoichi Ando

Appl. Phys. Lett. 86, 091910 (2005); http://dx.doi.org/10.1063/1.1864244 (3 pages) | Cited 89 times

Online Publication Date: 25 February 2005

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The oxygen-exchange behavior has been studied in half-doped manganese and cobalt perovskite oxides. We have found that the oxygen diffusivity in Gd0.5Ba0.5MnO3−δ can be enhanced by orders of magnitude by inducing crystallographic ordering among lanthanide and alkali-earth ions in the A-site sublattice. Transformation of a simple cubic perovskite, with randomly occupied A sites, into a layered crystal GdBaMn2O5+x (or isostructural GdBaCo2O5+x for cobalt oxide) with alternating lanthanide and alkali-earth planes reduces the oxygen bonding strength and provides disorder-free channels for ion motion, pointing to an efficient way to design new ionic conductors.
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66.30.J- Diffusion of impurities
66.30.H- Self-diffusion and ionic conduction in nonmetals
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
61.50.Lt Crystal binding; cohesive energy

Growth of single quantum dots on preprocessed structures: Single photon emitters on a tip

V. Zwiller, T. Aichele, F. Hatami, W. T. Masselink, and O. Benson

Appl. Phys. Lett. 86, 091911 (2005); http://dx.doi.org/10.1063/1.1869544 (3 pages) | Cited 6 times

Online Publication Date: 25 February 2005

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We have grown InP quantum dots in GaInP by gas-source molecular-beam epitaxy on sharp tips etched out of a GaAs substrate. The growth parameters were optimized to produce single quantum dots on the tips, predominantly at the edges. Intensity correlation measurements of the fluorescence from single dots on these tips reveal antibunched photon emision. We propose to use these tip structures with stable single photon emitters at their apex as active probes for further controlled experiments in quantum and nano-optics.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
73.21.La Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)

Correlation between the crystalline environment and optical property of Mn2+ ions in ZnGa2O4: Mn2+ phosphor

Jong Su Kim, Jin Su Kim, Tae Wan Kim, Sun Myung Kim, and Hong Lee Park

Appl. Phys. Lett. 86, 091912 (2005); http://dx.doi.org/10.1063/1.1869550 (3 pages) | Cited 22 times

Online Publication Date: 25 February 2005

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Sol-gel-driven ZnGa2O4:Mn2+ phosphors are annealed at various temperatures. As an increase of the annealing temperature of as-grown ZnGa2O4:Mn2+ phosphors, their lattice constants and crystallinities are increased. The resonance signal intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased as the annealing temperature is increased. The decay curves are well fitted with two simple exponential decay functions indicating the existence of two origins. Liquid nitrogen-temperature emission spectra show two emission peaks suggesting that they originate from Mn2+ ions on Td and on Oh sites. The emission intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased. The variation of the optical characteristics agrees with the concentration of Mn2+ ions at Td site and its site environment.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
78.55.Hx Other solid inorganic materials
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
81.40.Gh Other heat and thermomechanical treatments
61.66.Fn Inorganic compounds
61.72.S- Impurities in crystals
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