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26 Mar 2001

Volume 78, Issue 13, pp. 1805-1950

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Dielectric transition of nanostructured diamond films

Haitao Ye, Chang Q. Sun, Haitao Huang, and Peter Hing

Appl. Phys. Lett. 78, 1826 (2001); http://dx.doi.org/10.1063/1.1342047 (3 pages) | Cited 21 times

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The dielectric behavior of nanostructured diamond films has been investigated by using an impedance analyzer up to 500 °C. Impedance data are presented in the form of the Cole–Cole plot. It is found that: (i) the resistivity contributed both from bulk grain interior and grain boundary decreases with increasing temperature; (ii) above 250 °C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation; and (iii) the electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 to 0.67 eV at 250 °C. Similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. The dielectric transition is explained as the change of crystal field caused by the thermal expansion or by surface bond contraction of nanosized particles. © 2001 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
73.63.Bd Nanocrystalline materials
72.60.+g Mixed conductivity and conductivity transitions
71.55.Cn Elemental semiconductors
73.61.Cw Elemental semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.22.Gm Dielectric loss and relaxation

Linewidths of excitonic luminescence transitions in AlGaN alloys

Giuliano Coli, K. K. Bajaj, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 78, 1829 (2001); http://dx.doi.org/10.1063/1.1357212 (3 pages) | Cited 27 times

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In this work, we present a study of the behavior of linewidths of excitonic photoluminescence transitions measured at 10 K in AlGaN alloys as a function of Al concentration. Samples we have investigated are grown by low-pressure metalorganic chemical vapor deposition on (0001) oriented sapphire substrates with low-temperature GaN buffer layers. The Al composition ranged from 0%–35%. We find that the values of the excitonic linewidth increase as a function of Al concentration and agree very well with those calculated using a model in which the broadening effect is assumed to be due to compositional disorder in semiconductor alloys. The values of the excitonic linewidths measured in our samples are considerably smaller than those reported recently, thus attesting to the high quality of our samples. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Interfacial reactions between thin rare-earth-metal oxide films and Si substrates

Haruhiko Ono and Tooru Katsumata

Appl. Phys. Lett. 78, 1832 (2001); http://dx.doi.org/10.1063/1.1357445 (3 pages) | Cited 118 times

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Rare-earth-metal oxide films (Ln2O3; Ln=Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb) between 20 and 30 nm thick were grown on Si substrates by using a pyrolysis method. We found that a silicate (LnSiO) layer and a silicon oxide layer were formed at the interface between oxides and substrate after postannealing. The infrared absorption of the Si–O–Ln bonds increased as the postannealing temperature rose. The Si–O–Ln bond formation strongly depended on the ion radii of the rare-earth elements. We conclude that an interfacial silicate layer can easily be formed by a reaction with Si atoms diffusing from the substrate for oxides with larger ion radii. This is because such oxides may have a larger space between atoms. The quantity of Si–O–Si bonds also increased after postannealing. The increase in the Si–O–Si bonds for Ln2O3 was independent of the elements, and almost the same as the increases for Ta2O5 and ZrO2. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Spontaneous ridge-structure formation and large field emission of heavily Si-doped AlN

Makoto Kasu and Naoki Kobayashi

Appl. Phys. Lett. 78, 1835 (2001); http://dx.doi.org/10.1063/1.1357449 (3 pages) | Cited 11 times

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Sharp ridge structures with a 3 nm wide (0001) top facet and {1math01} sidewall facets formed on the surface of a heavily Si-doped AlN layer on a 6H-SiC (0001) substrate during metalorganicvapor-phase-epitaxy growth. This is caused by {1math01} facet growth induced by heavy Si doping. We obtained a large field emission (FE) current density of 11 mA/cm2 at 84 V/μm. One of the reasons for the large FE is that the ridge-structure formation decreases the energy barrier necessary for FE by about 2.4 eV. © 2001 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

In situ analysis of the room-temperature epitaxial growth of CeO2 ultrathin films on Si (111) by coaxial impact-collision ion scattering spectroscopy

M. Furusawa, J. Tashiro, A. Sasaki, K. Nakajima, M. Takakura, T. Chikyow, P. Ahmet, and M. Yoshimoto

Appl. Phys. Lett. 78, 1838 (2001); http://dx.doi.org/10.1063/1.1356451 (3 pages) | Cited 6 times

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The room-temperature epitaxial growth of CeO2 films on Si(111) substrates was examined in situ by combined use of a coaxial impact-collision ion scattering spectroscopy (CAICISS) and the laser molecular beam epitaxy (laser MBE). It was found that the crystal quality of CeO2 ultrathin films (∼3 nm thick) as-grown in UHV ( ∼ 10−9 Torr) could be improved remarkably by a few minutes of O2 gas exposure ( ∼ 10−5 Torr) at room temperature. A three-fold symmetry in the Ce signal intensity of azimuth rotational CAICISS spectra, which exhibited the type-B epitaxial growth ([math10]CeO2‖[1math0]Si), was observed for the films thicker than about 1 nm. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Fg Pulsed laser ablation deposition

Formation of a nanoquasicrystalline phase in Zr–Cu–Ti–Ni metallic glass

Dmitri V. Louzguine and Akihisa Inoue

Appl. Phys. Lett. 78, 1841 (2001); http://dx.doi.org/10.1063/1.1358362 (3 pages) | Cited 16 times

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Structure changes in Zr–Ti–Ni–Cu metallic glass on heating have been studied by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. It has been found that the first stage of the devitrification process is related to the precipitation of fine particles of an icosahedral phase from about 3 to 7 nm in size. Direct evidence of the formation of the icosahedral phase has been obtained using nanobeam diffraction in transmission electron microscopy. © 2001 American Institute of Physics.
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61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
61.44.Br Quasicrystals
64.70.K- Solid-solid transitions
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Modification of refractive index in Ag/Na ion-exchanged glasses by vacuum-ultraviolet pulse laser irradiation

S. Ruschin, K. Sugioka, G. Yarom, T. Akane, and K. Midorikawa

Appl. Phys. Lett. 78, 1844 (2001); http://dx.doi.org/10.1063/1.1357216 (3 pages) | Cited 2 times

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Laser-induced refractive index modification in Ag+ ion exchanged waveguides on glass substrates was observed. Waveguiding effects were measured, and an increase in refractive index of more than 2×10−3 was deduced. Refractive index profiles show that the maximum radiation-induced difference is attained 4–5 μm below the surface. Possible mechanisms for the material modification are discussed. © 2001 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.82.Et Waveguides, couplers, and arrays
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.Pg Disordered solids
42.79.Gn Optical waveguides and couplers
61.82.Ms Insulators

Soft x-ray-excited luminescence and optical x-ray absorption fine structures of tris (8-hydroxyquinoline) aluminum

S. J. Naftel, P. Zhang, P.-S. Kim, T. K. Sham, I. Coulthard, W. J. Antel, J. W. Freeland, S. P. Frigo, M.-K. Fung, S. T. Lee, Y. F. Hu, and B. W. Yates

Appl. Phys. Lett. 78, 1847 (2001); http://dx.doi.org/10.1063/1.1358360 (3 pages) | Cited 8 times

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Photoluminescence from tris (8-hydroxyquinoline) aluminum (Alq3) films has been observed using tunable soft x rays as an excitation source. The photons were tuned to energies above and below the K absorption edges of C, N, O, and Al. The luminescence was in turn used to monitor the absorption. It was found that the luminescence induced by soft x ray exhibits additional emission bands at shorter wavelengths compared to ultraviolet excitation. While all K edges exhibit optical x-ray absorption fine structures (XAFS) similar to those of total electron and fluorescence yield, the optical XAFS at the C K-edge resonance are enhanced for the C1s to π∗ transitions, indicating site specificity. These observations are attributed to the energetics of the process and the local electronic structure. © 2001 American Institute of Physics.
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78.55.Kz Solid organic materials
78.70.Dm X-ray absorption spectra

Near-unity below-band-gap absorption by microstructured silicon

C. Wu, C. H. Crouch, L. Zhao, J. E. Carey, R. Younkin, J. A. Levinson, E. Mazur, R. M. Farrell, P. Gothoskar, and A. Karger

Appl. Phys. Lett. 78, 1850 (2001); http://dx.doi.org/10.1063/1.1358846 (3 pages) | Cited 115 times

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We increased the absorptance of light by silicon to approximately 90% from the near ultraviolet (0.25 μm) to the near infrared (2.5 μm) by surface microstructuring using laser-chemical etching. The remarkable absorptance most likely comes from a high density of impurities and structural defects in the silicon lattice, enhanced by surface texturing. Microstructured avalanche photodiodes show significant enhancement of below-band-gap photocurrent generation at 1.06 and 1.31 μm, indicating promise for use in infrared photodetectors. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
85.60.Dw Photodiodes; phototransistors; photoresistors
42.62.Cf Industrial applications
78.30.Hv Other nonmetallic inorganics
78.40.Fy Semiconductors

Surfactant-assisted synthesis of semiconductor nanotubes and nanowires

C. N. R. Rao, A. Govindaraj, F. Leonard Deepak, N. A. Gunari, and Manashi Nath

Appl. Phys. Lett. 78, 1853 (2001); http://dx.doi.org/10.1063/1.1359145 (3 pages) | Cited 100 times

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Nanotubes and nanowires of CdSe and CdS have been obtained from solutions containing a surfactant such as Triton 100-X. They have been characterized by x-ray diffraction, electron microscopy, and optical spectroscopy. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Be Chemical synthesis methods
61.46.-w Structure of nanoscale materials
78.67.Ch Nanotubes
78.55.Et II-VI semiconductors

Evidence of a stable binary CdCa quasicrystalline phase

J. Z. Jiang, C. H. Jensen, A. R. Rasmussen, and L. Gerward

Appl. Phys. Lett. 78, 1856 (2001); http://dx.doi.org/10.1063/1.1359147 (2 pages) | Cited 6 times

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Quasicrystals with a primitive icosahedral structure and a quasilattice constant of 5.1215 Å have been synthesized in a binary Cd–Ca system. The thermal stability of the quasicrystal has been investigated by in situ high-temperature x-ray powder diffraction using synchrotron radiation. It is demonstrated that the binary CdCa quasicrystal is thermodynamic stable up to its melting temperature. The linear thermal expansion coefficient of the quasicrystal is 2.765×10−5 K−1. © 2001 American Institute of Physics.
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61.44.Br Quasicrystals
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Photoluminescence of Ge quantum dots prepared on porous silicon by ultrahigh vacuum chemical vapor deposition

Jingyun Huang, Zhizhen Ye, Binghui Zhao, Xiangyang Ma, Yadong Wang, and Duanlin Que

Appl. Phys. Lett. 78, 1858 (2001); http://dx.doi.org/10.1063/1.1359144 (3 pages) | Cited 3 times

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This letter reports a way of preparing Ge quantum dots on anodized porous silicon layers by ultrahigh vacuum chemical vapor deposition at a low temperature of 720 °C. The porous silicon was formed by anodic conversion of p-type (100) oriented crystalline silicon in hydrofluoric acid diluted by alcohol. A clear phonon-resolved photoluminescence (PL), as a no-phonon (NP) and its transverse acoustic phonon replica, was observed from the Ge dots at the temperature of 10 K. The blueshift energy is as high as about 136 meV, but the full width at half maximum of the NP PL spectrum is only 1.23 meV. We attributed the very large blueshift in energy of the PL peak to quantum size confinement effect of the Ge quantum dots. © 2001 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Piezoelectric contributions to pulsed degenerate four-wave mixing

Ivan Biaggio

Appl. Phys. Lett. 78, 1861 (2001); http://dx.doi.org/10.1063/1.1358850 (3 pages) | Cited 6 times

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The existence of geometry and pulse-length-dependent piezoelectric contributions to pulsed degenerate four-wave mixing is demonstrated experimentally. These effects must be taken into account when measuring third-order susceptibilities in noncentrosymmetric materials. © 2001 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.65.An Optical susceptibility, hyperpolarizability
42.70.Mp Nonlinear optical crystals
78.20.Jq Electro-optical effects
77.65.-j Piezoelectricity and electromechanical effects

Formation of the TiSi2 C40 as an intermediate phase during the reaction of the Si/Ta/Ti system

F. La Via, F. Mammoliti, G. Corallo, M. G. Grimaldi, D. B. Migas, and Leo Miglio

Appl. Phys. Lett. 78, 1864 (2001); http://dx.doi.org/10.1063/1.1359142 (3 pages) | Cited 6 times

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The effect of a thin Ta layer at the Si/Ti interface on the intermediate phase formation has been studied in detail by in situ sheet resistance, x-ray diffraction, transmission electron microscopy and Rutherford backscattering spectroscopy of partially reacted samples. When a Ta layer is deposited at the Si/Ti interface, a new intermediate phase has been detected, i.e. the hexagonal TiSi2 C40. This phase grows on the C40–TaSi2 that is formed at the interface with silicon. The lattice parameters of the C40–TiSi2 obtained by ab initio calculations agree quite well with the experimental ones. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Dv Composition, segregation; defects and impurities
73.40.Ns Metal-nonmetal contacts
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.37.Lp Transmission electron microscopy (TEM)
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing
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