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10 Dec 2007

Volume 91, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 91, 241101 (2007); http://dx.doi.org/10.1063/1.2821382 (3 pages)

S. N. Goda, S. Sensarn, M. Y. Shverdin, and G. Y. Yin
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Interfacial characteristics and band alignments for ZrO2 gate dielectric on Si passivated p-GaAs substrate

Goutam Kumar Dalapati, Aaditya Sridhara, Andrew See Weng Wong, Ching Kean Chia, Sung Joo Lee, and Dongzhi Chi

Appl. Phys. Lett. 91, 242101 (2007); http://dx.doi.org/10.1063/1.2822422 (3 pages) | Cited 19 times

Online Publication Date: 10 December 2007

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The interfacial characteristics and band alignments of high-k ZrO2 on p-GaAs have been investigated by using x-ray photoelectron spectroscopy and electrical measurements. It has been demonstrated that the presence of Si interfacial passivation layer (IPL) improves GaAs metal-oxide-semiconductor device characteristics such as interface state density, accumulation capacitance, and hysteresis. It is also found that Si IPL can reduce interfacial GaAs-oxide formation and increases effective valence-band offset at ZrO2/p-GaAs interface. The effective valence-band offsets of ZrO2/p-GaAs and ZrO2/Si/p-GaAs interfaces are determined to be 2.7 and 2.84 eV, while the effective conduction-band offsets are found to be 1.67 and 1.53 eV, respectively.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Rv Passivation
85.30.Tv Field effect devices
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Enhancement of Seebeck coefficient for SrO(SrTiO3)2 by Sm substitution: Crystal symmetry restoration of distorted TiO6 octahedra

Yifeng Wang, Kyu Hyoung Lee, Hideki Hyuga, Hideki Kita, Katsuhiko Inaba, Hiromichi Ohta, and Kunihito Koumoto

Appl. Phys. Lett. 91, 242102 (2007); http://dx.doi.org/10.1063/1.2820447 (3 pages) | Cited 5 times

Online Publication Date: 10 December 2007

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We found that Sm3+ substitution in SrO(SrTiO3)2 is effective in improving the Seebeck coefficient (S). The ∣S∣ value increases notably with temperature, benefiting from an enhancement of the density of states (DOS) effective mass md* from ∼ 3m0 (300 K) to  ∼ 7.5m0 (1000 K), due to an improvement of the local symmetry of TiO6 octahedra, enhancing the degeneracy in the Ti 3d orbitals, which form the conduction band (CB), and also to an accompanying lattice expansion, which gives rise to a higher DOS at the bottom of the CB and, consequently, a larger md*.
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73.50.Lw Thermoelectric effects
73.61.Le Other inorganic semiconductors
71.20.Ps Other inorganic compounds
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
72.20.Pa Thermoelectric and thermomagnetic effects

Trap-controlled hole transport in small molecule organic semiconductors

Arne Fleissner, Hanna Schmid, Christian Melzer, and Heinz von Seggern

Appl. Phys. Lett. 91, 242103 (2007); http://dx.doi.org/10.1063/1.2820448 (3 pages) | Cited 8 times

Online Publication Date: 11 December 2007

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The influence of trap concentration on hole transport is investigated by an optical time-of-flight method for the amorphous small molecule organic semiconductor N,N′-bis(1-naphtyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamin (α-NPD) doped with neutral hole traps by codeposition of 4,4′,4″-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA). α-NPD doped with 120 ppm 1-NaphDATA exhibits nondispersive hole transport like undoped α-NPD, but trap-controlled with reduced mobility. The trap depth derived from the mobility decrease coincides with the ionization potential difference of α-NPD and 1-NaphDATA. The transition to dispersive transport for increasing trap concentration to 1160 ppm is explained by an energetic relaxation of optically generated charge carriers within a density of states broadened by traps.
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72.20.Fr Low-field transport and mobility; piezoresistance
81.05.Hd Other semiconductors
72.80.Le Polymers; organic compounds (including organic semiconductors)

Giant tunnel magnetoresistance in codeposited fullerene-cobalt films in the low bias-voltage regime

Seiji Sakai, Isamu Sugai, Seiji Mitani, Koki Takanashi, Yoshihiro Matsumoto, Hiroshi Naramoto, Pavel V. Avramov, Satoru Okayasu, and Yoshihito Maeda

Appl. Phys. Lett. 91, 242104 (2007); http://dx.doi.org/10.1063/1.2822397 (3 pages) | Cited 16 times

Online Publication Date: 12 December 2007

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Magnetotransport properties in the low bias-voltage regime were investigated for codeposited C60–Co films. A giant tunnel magnetoresistance (MR) ratio (ΔR/Rmax) of 80%, which is the highest in ferromagnetic metal/organic molecule systems, was found at low temperatures. The observed bias-voltage dependence of the MR ratio is expressed by an unusual exponential form, suggesting that the MR ratio of nearly 100% can be realized in the low bias-voltage limit.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
81.05.ub Fullerenes and related materials
75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Effects of strain and interface on work function of a Nb–W metal gate system

H. R. Gong, Yoshio Nishi, and Kyeongjae Cho

Appl. Phys. Lett. 91, 242105 (2007); http://dx.doi.org/10.1063/1.2821225 (3 pages) | Cited 10 times

Online Publication Date: 12 December 2007

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First principles calculation reveals that the compressed (tensile) strain increases (decreases) the work function of Nb and W (110) surfaces, and that such a work function change is due to the combined effects of the surface dipole and bulk electronic structure toward the same direction. Calculation also shows that the interface dipole is formed in the Nb–W interface due to an unequal loss of the electrons from Nb and W interface atoms, and that the formation of the Nb–W interface is energetically favorable with negative interface energy, implying a tendency of interface interdiffusion of Nb and W atoms.
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73.40.Cg Contact resistance, contact potential
73.30.+y Surface double layers, Schottky barriers, and work functions
73.20.At Surface states, band structure, electron density of states
68.35.Md Surface thermodynamics, surface energies
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Gy Mechanical properties; surface strains

Spin-dependent scattering off neutral antimony donors in 28Si field-effect transistors

C. C. Lo, J. Bokor, T. Schenkel, A. M. Tyryshkin, and S. A. Lyon

Appl. Phys. Lett. 91, 242106 (2007); http://dx.doi.org/10.1063/1.2817966 (3 pages) | Cited 18 times

Online Publication Date: 12 December 2007

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We report measurements of spin-dependent scattering of conduction electrons by neutral donors in accumulation-mode field-effect transistors formed in isotopically enriched silicon. Spin-dependent scattering was detected using electrically detected magnetic resonance where spectra show resonant changes in the source-drain voltage for conduction electrons and electrons bound to donors. We discuss the utilization of spin-dependent scattering for the readout of donor spin states in silicon based quantum computers.
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72.25.-b Spin polarized transport
85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Electret mechanism, hysteresis, and ambient performance of sol-gel silica gate dielectrics in pentacene field-effect transistors

T. Cahyadi, H. S. Tan, S. G. Mhaisalkar, P. S. Lee, F. Boey, Z.-K. Chen, C. M. Ng, V. R. Rao, and G. J. Qi

Appl. Phys. Lett. 91, 242107 (2007); http://dx.doi.org/10.1063/1.2821377 (3 pages) | Cited 7 times

Online Publication Date: 12 December 2007

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The electret induced hysteresis was studied in sol-gel silica films that result in higher drain currents and improved device performance in pentacene field-effect transistors. Vacuum and ambient condition studies of the hysteresis behavior and capacitance-voltage characteristics on single layer and varying thicknesses of bilayer dielectrics confirmed that blocking layers of thermal oxide could effectively eliminate the electret induced hysteresis, and that thin (25 nm) sol-gel silica dielectrics enabled elimination of nanopores thus realizing stable device characteristics under ambient conditions.
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85.30.Tv Field effect devices
77.55.-g Dielectric thin films

Schottky barrier height tuning of silicide on Si1−xCx

Mantavya Sinha, Eng Fong Chor, and Chung Foong Tan

Appl. Phys. Lett. 91, 242108 (2007); http://dx.doi.org/10.1063/1.2820386 (3 pages) | Cited 6 times

Online Publication Date: 14 December 2007

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We have demonstrated the tuning of Schottky barrier height (SBH) of nickel silicide on silicon-carbon (Si1−xCx) by varying the carbon mole fraction, x. The SBH (for electron conduction) has been found to decrease with carbon concentration at a rate of ∼ 6.6 meV/ (0.1% carbon). We have achieved ∼ 27 meV drop in SBH with 0.4% carbon incorporation in Si1−xCx and shown that 1.3% carbon could lead to more than 85 meV improvement. Furthermore, our results show an avenue to reduce the SBH of rare earth silicide contacts in n-channel Schottky transistors by fabricating them on Si1−xCx.
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73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Tv Field effect devices

106 years extrapolated hole storage time in GaSb/AlAs quantum dots

A. Marent, M. Geller, A. Schliwa, D. Feise, K. Pötschke, D. Bimberg, N. Akçay, and N. Öncan

Appl. Phys. Lett. 91, 242109 (2007); http://dx.doi.org/10.1063/1.2824884 (3 pages) | Cited 25 times

Online Publication Date: 14 December 2007

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A thermal activation energy of 710 meV for hole emission from InAs/GaAs quantum dots (QDs) across an Al0.9Ga0.1As barrier is determined by using time-resolved capacitance spectroscopy. A hole storage time of 1.6 s at room temperature is directly measured, being three orders of magnitude longer than a typical dynamic random access memory (DRAM) refresh time. The dependence of the hole storage time in different III–V QDs on their localization energy is determined and the localization energies in GaSb-based QDs are calculated using eight-band k⋅p theory. A storage time of about 106 years in GaSb/AlAs QDs is extrapolated, sufficient for a QD-based nonvolatile (flash) memory.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
73.63.Kv Quantum dots
73.61.Ey III-V semiconductors
73.21.La Quantum dots

Percolative effects on noise in pentacene transistors

B. R. Conrad, W. G. Cullen, W. Yan, and E. D. Williams

Appl. Phys. Lett. 91, 242110 (2007); http://dx.doi.org/10.1063/1.2823577 (3 pages) | Cited 11 times

Online Publication Date: 14 December 2007

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Noise in pentacene thin film transistors has been measured as a function of device thickness from well above the effective conduction channel thickness to only two conducting layers. Over the entire thickness range, the spectral noise form is 1/f, and the noise parameter varies inversely with gate voltage, confirming that the noise is due to mobility fluctuations, even in the thinnest films. Hooge’s parameter varies as an inverse power law with conductivity for all film thicknesses. The magnitude and transport characteristics of the spectral noise are well explained in terms of percolative effects arising from the grain boundary structure.
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85.30.Tv Field effect devices

Systematic study on p-type doping control of InN with different Mg concentrations in both In and N polarities

Xinqiang Wang, Song-Bek Che, Yoshihiro Ishitani, and Akihiko Yoshikawa

Appl. Phys. Lett. 91, 242111 (2007); http://dx.doi.org/10.1063/1.2824816 (3 pages) | Cited 27 times

Online Publication Date: 14 December 2007

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p-type conductivity control of In- and N-polar InN layers grown on GaN templates with different Mg concentrations ([Mg]) was systematically investigated by using electrolyte-based capacitance-voltage (ECV) analyses. With increasing [Mg], p-type conduction was confirmed for [Mg]s from ∼ 1018 to  ∼ 3×1019 cm−3. The conduction was reversed to n type at [Mg]s above 1020 cm−3, however, due to overdoping effects introducing shallow donors in InN. Further, it was found that charges at the interface states located within forbidden band of InN greatly affected the ECV measurements resulting in overestimation of net acceptor concentrations, and some calibration was necessary to estimate them.
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73.61.Ey III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.20.At Surface states, band structure, electron density of states
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