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1 Nov 2006

Volume 100, Issue 9, Articles (09xxxx)

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On the origin of unusual transport properties observed in densely packed polycrystalline CaAl2

S. Sergeenkov and F. M. Araujo-Moreira

J. Appl. Phys. 100, 096101 (2006); http://dx.doi.org/10.1063/1.2364667 (2 pages)

Online Publication Date: 1 November 2006

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A possible origin of unusual temperature behavior of transport coefficients observed in densely packed polycrystalline CaAl2 compound [ M. Ausloos et al., J. Appl. Phys., 96, 7338 (2004) ] is discussed, including a powerlike dependence of resistivity with ρ∝T−3/4 and N-like form of the thermopower. All these features are found to be in good agreement with the Shklovskii-Efros localization scenario [ Electronic Properties of Doped Semiconductors (Springer, Berlin, 1984) ] assuming polaron-mediated hopping processes controlled by the Debye energy.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.25.F- Transport properties
74.20.Mn Nonconventional mechanisms

Comment on “Optical characterization of CuIn1−xGaxSe2 alloy thin films by spectroscopic ellipsometry” [ J. Appl. Phys. 94, 879 (2003) ]

Sung-Ho Han and Dean Levi

J. Appl. Phys. 100, 096102 (2006); http://dx.doi.org/10.1063/1.2374223 (2 pages)

Online Publication Date: 2 November 2006

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A method to determine the optical functions of thin-film CuIn1−xGaxSe2 alloys was provided in the paper “Optical characterization of CuIn1−xGaxSe2 alloy thin films by spectroscopic ellipsometry.” The optical functions were obtained and the effect of Ga content on the electronic transitions of CuIn1−xGaxSe2 was discussed. We indicate the mistake of their method in determining the critical point energies and discuss the reason for using standard analytic line shape, math(ω) = C−Aeiϕ(ω−E+iΓ)n, in this comment.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Dust charge effects on the resonant instability of the dust-acoustic wave in a semibounded dusty plasma

Hwa-Min Kim and Young-Dae Jung

J. Appl. Phys. 100, 096103 (2006); http://dx.doi.org/10.1063/1.2372414 (3 pages)

Online Publication Date: 3 November 2006

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The resonant instability of the surface dust-acoustic wave is investigated in a semibounded dusty plasma containing elongated and rotating dust grains. The temporal growth rate of the surface dust-acoustic instability is obtained by the plasma dielectric function with the specular reflection boundary condition. The results show that the domain of the instability increases with increase in the wave number, especially for the case of the negatively charged dust grains. It is also found that the growth rate of the instability with negatively charged dust grains is found to be smaller than that with positively charged dust grains. In addition, it is found that the growth rate decreases with increasing the ratio of the dust plasma frequency to the rotation frequency.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Dm Sound waves
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Mq Dielectric properties

247 nm solar-blind ultraviolet p-i-n photodetector

V. V. Kuryatkov, B. A. Borisov, S. A. Nikishin, Yu. Kudryavtsev, R. Asomoza, V. I. Kuchinskii, G. S. Sokolovskii, D. Y. Song, and M. Holtz

J. Appl. Phys. 100, 096104 (2006); http://dx.doi.org/10.1063/1.2364049 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2006

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We describe solar-blind p-i-n photodetectors based on short period superlattices of AlN/Al0.08Ga0.92N. The devices are grown using gas source molecular beam epitaxy with ammonia on transparent sapphire substrates. The cutoff wavelength for the device is 247 nm. For diodes with 150 μm diameter mesas and sidewall surfaces passivated in oxygen plasma, we obtain extremely low dark leakage current of ∼ 3 pA/cm2 and high zero-bias resistance of ∼ 6×1014 Ω. At 10 V reverse bias the observed responsivity is 62 mA/W.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

Carrier generation and transport properties of heavily Nb-doped anatase TiO2 epitaxial films at high temperatures

Daisuke Kurita, Shingo Ohta, Kenji Sugiura, Hiromichi Ohta, and Kunihito Koumoto

J. Appl. Phys. 100, 096105 (2006); http://dx.doi.org/10.1063/1.2362990 (3 pages) | Cited 52 times

Online Publication Date: 7 November 2006

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To compare the intrinsic thermoelectric (TE) properties of heavily Nb-doped TiO2 to those of heavily Nb-doped SrTiO3 [ S. Ohta et al., Appl. Phys. Lett. 87, 092108 (2005) ], the electrical conductivity (σ), carrier concentration (ne), Hall mobility (μHall), and Seebeck coefficient (S) of heavily Nb-doped TiO2 (anatase) epitaxial films were measured at high temperatures (300–900 K). The epitaxial films were grown on the (100)-face of LaAlO3 single-crystalline substrates by a pulsed-laser deposition technique at 800 °C. The carrier effective mass (m*) of the anatase TiO2 epitaxial films was ∼ 1m0, which is an order of magnitude smaller than that of Nb-doped SrTiO3 ( ∼ 10m0). The estimated TE power factor (S2σ) of the ∼ 2%-Nb-doped anatase TiO2 film (ne ∼ 5×1020 cm−3) was ∼ 2.5×10−4 W m−1 K−2 at 900 K, which is approximately 15% of the 20%-Nb-doped SrTiO3 (1.5×10−3 W m−1 K−2). The present findings will help establish a future TE material design concept for Ti-based metal oxides.
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72.20.Pa Thermoelectric and thermomagnetic effects
61.72.S- Impurities in crystals
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.61.Ng Insulators

Control of the thin film properties of Cu(In,Ga)Se2 using water vapor introduction during growth

Shogo Ishizuka, Hajime Shibata, Akimasa Yamada, Paul Fons, Keiichiro Sakurai, Koji Matsubara, Shigeru Niki, Minoru Yonemura, and Hisayuki Nakanishi

J. Appl. Phys. 100, 096106 (2006); http://dx.doi.org/10.1063/1.2362991 (3 pages) | Cited 2 times

Online Publication Date: 7 November 2006

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The effects of water vapor introduction during growth on Cu(In,Ga)Se2 (CIGSe) thin film properties, specifically the electrical and photoluminescence (PL) properties have been studied. Increases in the hole carrier density and conductivity with water vapor introduction were observed for all [Ga]/[In+Ga] composition ratios. The PL spectra observed from CuGaSe2 (CGSe) showed an annihilation of deep donor-acceptor pair emissions related to Se vacancies with water vapor introduction. In addition, the Na content in the CIGSe layers as well as the O content was found to increase. These results suggest that the mechanism behind the variation observed in the electrical and PL properties and consequent cell improvement is largely attributable to a decrease in the Se-vacancies-induced donor defect density and an enhancement of Na effects.
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73.61.Le Other inorganic semiconductors
68.55.-a Thin film structure and morphology
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
61.72.J- Point defects and defect clusters

Temporal evolution of ion fragment production from methylsilane by a hot tungsten wire

Satoru Yoshimura, Akinori Toh, Takahiro Toyoshima, Masato Kiuchi, and Satoshi Hamaguchi

J. Appl. Phys. 100, 096107 (2006); http://dx.doi.org/10.1063/1.2364050 (3 pages) | Cited 2 times

Online Publication Date: 8 November 2006

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Temporal evolution of ion fragment production from gaseous methylsilane in contact with a hot tungsten wire was measured with a use of a low-energy mass analyzed ion beam system. The mechanisms of molecular fragmentation in the system are similar to those for typical catalytic chemical vapor deposition processes. The fragmentation rates vary during the process due to surface modification of the tungsten wire. The extent of surface modification depends on the tungsten temperature. When the tungsten temperature was set to 1940 °C, ion fragments were produced initially but the production terminated about 1 h after the start of the experiment. The termination of ion production seems to be caused by the formation of a thick 3C-SiC layer on the tungsten surface, which was identified by x-ray diffraction measurement. When the tungsten temperature was set to 2220 °C, ion fragment production continued at least for 8 h. In this case the layer of deposited compounds, which mainly consist of WC, W2C, C, and 4H-SiC, was relatively thin.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Stoichiometry control of sputtered CuCl thin films: Influence on ultraviolet emission properties

Gomathi Natarajan, R. T. Rajendra Kumar, S. Daniels, D. C. Cameron, and P. J. McNally

J. Appl. Phys. 100, 096108 (2006); http://dx.doi.org/10.1063/1.2364665 (3 pages) | Cited 1 time

Online Publication Date: 9 November 2006

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We demonstrate that the chemical composition of the sputtered CuCl thin films could be finely controlled by adjusting the bias to the substrate. The films deposited without any intentional bias were Cl rich (CuCl1+x), a bias of −22 V yielded stoichiometric CuCl, and a further increase in the negative bias resulted in Cl deficient films (CuCl1−x). The crystalline and optical properties were found to be associated with the chemical composition. Cl rich films showed a deep level green emission at around 515 nm in addition to ultraviolet (UV) excitonic emission. The stoichiometric films have higher optical quality, exhibiting a sharp UV emission at around 385 nm at room temperature, compared to nonstoichiometric samples. Visible luminescence related to deep level defects was not observed in the stoichiometric films. Changes in energy of the flux from the target and the subsequent ion bombardment on the substrate surface are correlated with the variations in chemical composition and their impact on the film microstructure and UV emission.
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82.80.-d Chemical analysis and related physical methods of analysis
68.55.-a Thin film structure and morphology
71.55.Ht Other nonmetals
78.40.Fy Semiconductors
71.35.-y Excitons and related phenomena
78.66.Li Other semiconductors

Orientation dependence of ferroelectric and piezoelectric properties of Bi3.15Nd0.85Ti3O12 thin films on Pt(100)/TiO2/SiO2/Si substrates

G. D. Hu

J. Appl. Phys. 100, 096109 (2006); http://dx.doi.org/10.1063/1.2364668 (3 pages) | Cited 14 times

Online Publication Date: 10 November 2006

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Bi3.15Nd0.85Ti3O12 (BNT0.85) thin films with (100) [α(100) = 87.8%], (117) [α(117) = 77.1%], and (001) [α(001) = 98.8%] preferred orientations were deposited on Pt(100)/TiO2/SiO2/Si substrates using a metal organic decomposition process. The remanent polarization of (100)-predominant BNT0.85 film is about 50% and three times larger than those of (117)-preferred and (001)-oriented films, respectively, suggesting that the major polarization vector of BNT0.85 is close to the a axis rather than the c axis. This result can be further demonstrated by the piezoelectric measurements using an atomic force microscope in the piezoresponse mode.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
68.55.-a Thin film structure and morphology
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects

Response of two-defect magnetic photonic crystals to oblique incidence of light: Effect of defect layer variation

I. L. Lyubchanskii, N. N. Dadoenkova, M. I. Lyubchanskii, E. A. Shapovalov, A. E. Zabolotin, Y. P. Lee, and Th. Rasing

J. Appl. Phys. 100, 096110 (2006); http://dx.doi.org/10.1063/1.2362987 (3 pages) | Cited 7 times

Online Publication Date: 13 November 2006

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The transmission characteristics of a two-defect magnetic photonic crystal (MPC) with respect to oblique incident light are investigated, both for circularly polarized as well as linearly polarized light. It is shown that the transmittivity and Faraday rotation angle are very sensitive to a change of light propagation direction inside the MPC. Possible applications of MPCs as Faraday rotators are discussed.
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42.70.Qs Photonic bandgap materials
78.20.Ls Magneto-optical effects

Charging mechanism in a SiO2 matrix embedded with Si nanocrystals

Y. Liu, T. P. Chen, L. Ding, S. Zhang, Y. Q. Fu, and S. Fung

J. Appl. Phys. 100, 096111 (2006); http://dx.doi.org/10.1063/1.2374929 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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One of the applications of a Si nanocrystals (nc-Si) embedded in a SiO2 matrix is in the area of nonvolatile memory devices based on the charge storage in the material system. However, whether the charge trapping mainly occurs at the nc-Si/SiO2 interface or in the nc-Si is still unclear. In this work, by x-ray photoemission spectroscopy analysis of the Si 2p peaks, the concentrations of both the nc-Si and the Si suboxides that exist at the nc-Si/SiO2 interface are determined as a function of thermal annealing, and the charging effect is also measured by monitoring the shift of the surface C 1s peak. It is observed that the annealing-caused reduction of the total concentration of the interfacial suboxides is much faster than that of both the C 1s shift and the nc-Si concentration. In addition, the trend of the C 1s shift coincides with that of the nc-Si concentration. The results suggest that the Si nanocrystal, rather than the nc-Si/SiO2 interface, plays the dominant role in the charging effect.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Gh Other heat and thermomechanical treatments
73.63.Bd Nanocrystalline materials
61.72.up Other materials
61.80.Jh Ion radiation effects

Role of the Si/SiO2 interface during dopant diffusion in thin silicon on insulator layers

Giovanni Mannino, Antonino La Magna, Vittorio Privitera, Damiano Giubertoni, and Massimo Bersani

J. Appl. Phys. 100, 096112 (2006); http://dx.doi.org/10.1063/1.2374933 (3 pages)

Online Publication Date: 13 November 2006

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We found that As and B diffusion in 90 nm thick Si on SiO2, silicon on insulator, samples is reduced, by ∼ 20%, with respect to that of bulk Si for thermal processing in a lamp-based system. In contrast, when annealing is performed in a hot-wall furnace system and sample heating is determined by conduction diffusion length in Si–SiO2–Si samples is very similar to that occurring in bulk-Si reference samples. We demonstrate that diffusion in Si–SiO2–Si multilayer structures is primarily determined by an increased sample reflectivity, generated by the presence of the buried Si/SiO2 interface that reduces the amount of heat absorbed by the sample, rather than by the enhanced recombination of point defects at this interface. The latter phenomenon is not ruled out but plays a less relevant role in determining the measured reduction of diffusion.
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66.30.Fq Self-diffusion in metals, semimetals, and alloys
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.uf Ge and Si

Ferromagnetic interlayer coupling and switching process of exchange coupled composite media

W. K. Shen and Jian-Ping Wang

J. Appl. Phys. 100, 096113 (2006); http://dx.doi.org/10.1063/1.2374931 (3 pages) | Cited 12 times

Online Publication Date: 14 November 2006

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The ferromagnetic coupling effects in the exchange coupled composite (ECC) magnetic recording media were studied by varying the interlayer thickness and the saturation magnetization (Ms) of the soft layer. A minimum coercivity was observed at a certain interlayer thickness for the ECC media with a low Ms soft layer. When the Ms of the soft layer was increased (700 emu/cm3 in this work), no interlayer was needed to get the lowest coercivity for the ECC media, which makes the ECC media practical for a manufacturing process. A method to characterize the ferromagnetic coupling strength for the ECC media was quantitatively proposed. The switching process of the ECC media was observed to consist of the reversible switching of the soft layer and the irreversible switching of the hard layer.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-efficiency white organic light-emitting devices using a blue iridium complex to sensitize a red fluorescent dye

W. F. Xie, S. L. Chew, C. S. Lee, S. T. Lee, P. F. Wang, and H. L. Kwong

J. Appl. Phys. 100, 096114 (2006); http://dx.doi.org/10.1063/1.2374932 (3 pages) | Cited 6 times

Online Publication Date: 15 November 2006

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We report the fabrication of high-efficiency white organic light-emitting devices (WOLEDs) by using a blue phosphorescent dye iridium (III) tris(5-(2,4-difluoro-phenyl)-10,10-dimethyl- 4-aza-tricycloundeca-2,4,6-triene) (Ir(F2‐mppy)3) to sensitize the red dye[2-methyl-6- [2-(2,3,6,7-tetrahydro-1H c5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene]propane-din- itrile (DCM2). Ir(F2‐mppy)3 and DCM2 were codoped into the 4,4′‐N,N′-dicarbazole-biphenyl (CBP) host. The WOLEDs with 8 wt % Ir(F2‐mppy)3 and 0.5 wt % DCM2 showed white emission with a color rendering index of 70. The maximum luminance and maximum current efficiency of the device are, respectively, 16 220 cd/m2 and 9.28 cd/A.
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85.60.Jb Light-emitting devices
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