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7 May 2007

Volume 90, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 90, 193501 (2007); http://dx.doi.org/10.1063/1.2737344 (3 pages)

Peter Modregger, Daniel Lübbert, Peter Schäfer, and Rolf Köhler
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Amorphous gallium indium zinc oxide thin film transistors: Sensitive to oxygen molecules

Donghun Kang, Hyuck Lim, Changjung Kim, Ihun Song, Jaechoel Park, Youngsoo Park, and JaeGwan Chung

Appl. Phys. Lett. 90, 192101 (2007); http://dx.doi.org/10.1063/1.2723543 (3 pages) | Cited 91 times

Online Publication Date: 7 May 2007

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In this study, the authors report characteristic of indium gallium zinc oxides (GIZOs) which is strongly associated with the film surface. In ambient air, turn-on voltage of GIZO thin film transistors is approximately −7 V. However, at the pressure of 8×10−6 Torr, the turn-on voltage dramatically shifts to nearly −47 V of the negative gate bias direction. When the oxygen is introduced in the chamber, the turn-on voltage returns to the normal value, that of air. It is believed that the adsorbed oxygen forms depletion layer below the surface, resulting in Von shifts. The carrier concentration of the channel varies from 1×1019 to 1×1020 cm−3 due to oxygen adsorption.
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85.30.Tv Field effect devices

Evidence for trap-limited transport in the subthreshold conduction regime of chalcogenide glasses

Daniele Ielmini and Yuegang Zhang

Appl. Phys. Lett. 90, 192102 (2007); http://dx.doi.org/10.1063/1.2737137 (3 pages) | Cited 31 times

Online Publication Date: 7 May 2007

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The study of the temperature dependence of subthreshold conduction in amorphous chalcogenide materials reveals a voltage dependent activation energy, which can be attributed to trap-limited conduction. The authors find that the features of subthreshold conduction regime (subthreshold slope and activation energy) can be quantitatively explained by a simple conduction model for Poole-Frenkel transport in the presence of a high concentration of traps. This analysis allows for an accurate prediction of the temperature and voltage dependence of subthreshold current in amorphous chalcogenides, and offers a simple scheme for estimating the average distance between traps in the disordered material.
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72.80.Ng Disordered solids
72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

High-resolution characterization of ultrashallow junctions by measuring in vacuum with scanning spreading resistance microscopy

L. Zhang, K. Ohuchi, K. Adachi, K. Ishimaru, M. Takayanagi, and A. Nishiyama

Appl. Phys. Lett. 90, 192103 (2007); http://dx.doi.org/10.1063/1.2736206 (3 pages) | Cited 19 times

Online Publication Date: 8 May 2007

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The spatial resolution of scanning spreading resistance microscopy has been limited by using conventional probes when measuring in air. Sufficient electric contact of a probe-sample has been difficult to obtain in air due to the existence of moisture/contamination. Two-dimensional carrier profiling of nanoscale silicon devices is performed in a vacuum with conventional probes, and a high spatial resolution is obtained. Ultrashallow junctions down to 10 nm are measured accurately with high reproducibility. Experimental results show that a good electric contact between probe and sample is important for obtaining high spatial resolution.
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85.30.Tv Field effect devices
85.40.Ls Metallization, contacts, interconnects; device isolation

Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress

S. G. J. Mathijssen, M. Cölle, A. J. G. Mank, M. Kemerink, P. A. Bobbert, and D. M. de Leeuw

Appl. Phys. Lett. 90, 192104 (2007); http://dx.doi.org/10.1063/1.2737419 (3 pages) | Cited 13 times

Online Publication Date: 8 May 2007

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The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current.
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85.30.Tv Field effect devices

Shot noise spectroscopy of electronic spin flips in quantum dots

L. Y. Gorelik, S. I. Kulinich, R. I. Shekhter, M. Jonson, and V. M. Vinokur

Appl. Phys. Lett. 90, 192105 (2007); http://dx.doi.org/10.1063/1.2737421 (3 pages) | Cited 2 times

Online Publication Date: 8 May 2007

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Spin decoherence and spin flips crucially affect the tunneling transport of spin-polarized electrons through a quantum dot connected to magnetic leads. Here, the authors show that the low-frequency shot noise in such structures diverges as the spin relaxation rate for electrons on the dot goes to zero, reaching giant super-Poissonian values for realistic spin-flip rates. It is also shown that combined measurements of the average current and the shot noise as a function of bias voltage and external magnetic field offer a spectroscopic tool for studying electronic spin relaxation rates in this system.
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73.63.Kv Quantum dots
72.70.+m Noise processes and phenomena
73.40.Gk Tunneling

Giant anisotropic magnetoresistance and magnetothermopower in cubic 3:4 uranium pnictides

Piotr Wiśniewski

Appl. Phys. Lett. 90, 192106 (2007); http://dx.doi.org/10.1063/1.2737904 (3 pages) | Cited 1 time

Online Publication Date: 8 May 2007

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Temperature dependence of the anisotropic magnetoresistance and magnetothermopower of cubic ferromagnets U3As4 and U3P4 was examined on bulk single-crystal samples, in the range from 4.2 K to Curie points 198 and 138 K, respectively. The anisotropic magnetoresistance exceeding 50% was observed, which is about twice as big as that of Permalloys. Moreover, it changes its magnitude and sign with temperature. Such an unusual magnetoresistance is accompanied by anisotropic magnetothermopower also strongly varying with temperature. Applicability of a two-current model to explain the observed phenomena is discussed, and a complementary mechanism of anisotropy induced by trigonal distortion of crystal lattice is proposed.
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75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
72.20.Pa Thermoelectric and thermomagnetic effects
72.20.My Galvanomagnetic and other magnetotransport effects

Electronic structures and bonding properties of chlorine-treated nitrogenated carbon nanotubes: X-ray absorption and scanning photoelectron microscopy studies

S. C. Ray, C. W. Pao, H. M. Tsai, J. W. Chiou, W. F. Pong, C. W. Chen, M.-H. Tsai, P. Papakonstantinou, L. C. Chen, K. H. Chen, and W. G. Graham

Appl. Phys. Lett. 90, 192107 (2007); http://dx.doi.org/10.1063/1.2737392 (3 pages) | Cited 7 times

Online Publication Date: 8 May 2007

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The electronic and bonding properties of nitrogenated carbon nanotubes (N-CNTs) exposed to chlorine plasma were investigated using C and N K-edge x-ray absorption near-edge structure (XANES) and scanning photoelectron microscopy (SPEM). The C and N K-edge XANES spectra of chlorine-treated N-CNTs consistently reveal the formation of pyridinelike N-CNTs by the observation of 1s→π*(e2u) antibonding and 1s→π*(b2g) bonding states. The valence-band photoemission spectra obtained from SPEM images indicate that chlorination of the nanotubes enhances the C–N bonding. First-principles calculations of the partial densities of states in conjunction with C K-edge XANES data identify the presence of C–Cl bonding in chlorine treated N-CNTs.
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73.22.-f Electronic structure of nanoscale materials and related systems
71.20.Tx Fullerenes and related materials; intercalation compounds
52.77.-j Plasma applications
61.46.Fg Nanotubes
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Enhancement of room-temperature hole conductivity in narrow and strained Ge quantum well by double-side modulation doping

M. Myronov, Y. Shiraki, T. Mouri, and K. M. Itoh

Appl. Phys. Lett. 90, 192108 (2007); http://dx.doi.org/10.1063/1.2737396 (3 pages) | Cited 2 times

Online Publication Date: 8 May 2007

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The room-temperature two-dimensional hole gas (2DHG) conductivity as high as 649.3 μS is obtained by implementation of double-side modulation doping (DS-MOD) of an 8 nm thick strained Ge quantum well in a SiGe heterostructure. This conductivity is about three times higher than that of the conventional SiGe heterostructure with single-side modulation doping (SS-MOD). While the low-temperature (T = 3 K) mobility with DS-MOD is two times higher than that with SS-MOD, the room-temperature mobility of the two is practically the same, suggesting that phonon scattering is the dominant limiting mechanism at the device operating temperatures.
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73.63.Hs Quantum wells
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
72.20.Fr Low-field transport and mobility; piezoresistance
73.21.Fg Quantum wells

Effects of optical coupling in III-V multilayer systems

Carsten Baur, Martin Hermle, Frank Dimroth, and Andreas W. Bett

Appl. Phys. Lett. 90, 192109 (2007); http://dx.doi.org/10.1063/1.2737927 (3 pages) | Cited 9 times

Online Publication Date: 8 May 2007

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A method to visualize and investigate radiative recombination processes in compound semiconductor materials by utilizing the effect of optical coupling in III-V multilayer systems is presented. For this purpose, a semiconductor material of interest is grown on an activated germanium (Ge) substrate which then serves as a photodiode. By means of spectral response measurements of the Ge photodiode, a response signal from the upper layers can be detected. It is proven both by experiment and by modeling that the signals from these layers can only be explained by optical transport mechanisms, i.e., radiative recombination.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
85.60.Dw Photodiodes; phototransistors; photoresistors

Lattice vibrational properties of ZnMgO grown by pulsed laser deposition

A. I. Belogorokhov, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, E. A. Kozhukhova, H. S. Kim, D. P. Norton, and S. J. Pearton

Appl. Phys. Lett. 90, 192110 (2007); http://dx.doi.org/10.1063/1.2738196 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2007

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Vibrational modes were studied in n-type and p-type ZnMgO films doped with P (Mg composition of 7 at. %) grown by pulsed laser deposition on sapphire. The characteristic phonon frequencies were deduced from the analysis of IR reflectance measured by Fourier-transform spectroscopy. From comparison with similarly grown ZnO (P) films, Mg incorporation reduced the frequency of TO phonons by 14.5 cm−1 and introduced two Mg related modes near 530 and 969 cm−1. The first is likely to belong to the local vibrational mode of substitutional Mg, and the second is tentatively attributed to strongly lattice relaxed off-center Mg atoms. In addition, it was found that Mg incorporation triggers the formation of two phonon bands with characteristic frequencies of 501 and 634 cm−1 that most likely belong to lattice defects.
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63.20.-e Phonons in crystal lattices
78.30.Fs III-V and II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition

Dual-frequency resonant phonon scattering in BaxRyCo4Sb12 (R = La, Ce, and Sr)

J. Yang, W. Zhang, S. Q. Bai, Z. Mei, and L. D. Chen

Appl. Phys. Lett. 90, 192111 (2007); http://dx.doi.org/10.1063/1.2737422 (3 pages) | Cited 62 times

Online Publication Date: 9 May 2007

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Low temperature transport properties of polycrystalline dual-element-filled skutterudites BaxRyCo4Sb12 (R = La, Ce, and Sr) are reported. Remarkably the combination of Ba and La or Ba and Ce is much more effective in reducing lattice thermal conductivity (κL) than Ba and Sr. The density-functional theory calculations and experimental data suggest that multiple-filled skutterudites using filler elements of different chemical natures, such as the rare earths, the alkaline earths, or the alkalines provide a broader range of resonant phonon scattering. The thermoelectric figure of merit of filled skutterudites can likely be improved by means of such multiple-element void filling.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
72.20.Pa Thermoelectric and thermomagnetic effects

Charge transfer in nanocrystalline-Au/ZnO nanorods investigated by x-ray spectroscopy and scanning photoelectron microscopy

J. W. Chiou, S. C. Ray, H. M. Tsai, C. W. Pao, F. Z. Chien, W. F. Pong, M.-H. Tsai, J. J. Wu, C. H. Tseng, C.-H. Chen, J. F. Lee, and J.-H. Guo

Appl. Phys. Lett. 90, 192112 (2007); http://dx.doi.org/10.1063/1.2738369 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2007

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O K- and Zn and Au L3-edge x-ray absorption near-edge structure (XANES), x-ray emission spectroscopy (XES), and scanning photoelectron microscopy (SPEM) are performed to investigate the electronic structure of ZnO nanorods with nanocrystalline (nc)-Au particles grown on the surfaces. The XANES spectra of nc-Au/ZnO nanorods reveal the decrease of the number of both O 2p and Zn 4s/3d unoccupied states with the increase of the nc-Au particle size. The number of Au 6s/5d unoccupied states increases when the size of nc-Au particle decreases, indicating that the deposition of nc-Au particles on the surface of ZnO nanorods promotes charge transfer from the ZnO nanorods to nc-Au particles. Excitation energy dependent XES and SPEM spectra show that the number of electrons in the valence band of O 2p-Zn 4sp hybridized states decreases as the nc-Au particle size increases, revealing that more electrons are excited from the valence band to the conduction band of ZnO nanorods and the storage of electrons in nc-Au particles.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.70.Dm X-ray absorption spectra
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Fabrication of thick SiGe on insulator (Si0.2Ge0.8OI) by condensation of SiGe/Si superlattice grown on silicon on insulator

S. Balakumar, S. Peng, K. M. Hoe, G. Q. Lo, R. Kumar, N. Balasubramanian, D. L. Kwong, Y. L. Foo, and S. Tripathy

Appl. Phys. Lett. 90, 192113 (2007); http://dx.doi.org/10.1063/1.2737818 (3 pages) | Cited 7 times

Online Publication Date: 9 May 2007

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In this work, the authors demonstrate a fabrication methodology for obtaining a thick ( ∼ 250 nm) high Ge content SiGe-on-insulator (SGOI) film. About 800 nm thick low Ge content ( ∼ 25%) SGOI film was fabricated by intermixing SiGe and Si through thermal annealing of a superlattice comprising of 60 periods of Si0.7Ge0.3 and Si on silicon-on-insulator (SOI) substrate. A combination of oxidation and annealing processes was used to condense and diffuse the Ge through SiGe film to obtain thick Si0.2Ge0.8OI. It is also found that the oxidation termination is due to residual stress in the thick SGOI layer. The transmission electron microscopy measurements showed that the Si0.2Ge0.8OI film exhibits a single crystalline nature with an orientation that is the same as the starting SOI. X-ray diffraction measurements confirmed that the in-plane strain of the SGOI layers is compressive or nearly relaxed.
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81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
68.65.Cd Superlattices
61.72.Cc Kinetics of defect formation and annealing
81.65.Mq Oxidation
68.60.Bs Mechanical and acoustical properties

Photo-leakage-current characteristic of F incorporated hydrogenated amorphous silicon thin film transistor

M. C. Wang, T. C. Chang, Po-Tsun Liu, S. W. Tsao, and J. R. Chen

Appl. Phys. Lett. 90, 192114 (2007); http://dx.doi.org/10.1063/1.2738192 (3 pages) | Cited 3 times

Online Publication Date: 10 May 2007

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The photo-leakage-current (IPLC) characteristic of F incorporated a-Si:H thin film transistor (TFT) has been studied. The device activation energy (Ea) of a-Si:H(:F) TFTs is higher than those of typical a-Si:H TFTs, and resulted in the shift down of Fermi level in a-Si:H(:F). Experimental results show that the IPLC of a-Si:H(:F) TFTs is smaller than that of conventional a-Si:H TFTs in the density of states limited region, stemmed from the higher recombination centers present in a-Si:H(:F) material. However, the higher IPLC is observed in the hole conduction region, resulted from the larger Ea in the a-Si:H(:F) TFTs.
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85.30.Tv Field effect devices
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