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20 Dec 2004

Volume 85, Issue 25, pp. 6083-6293

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 6281 (2004); http://dx.doi.org/10.1063/1.1834720 (3 pages)

M. P. Rao, M. F. Aimi, and N. C. MacDonald
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Band tail hopping conduction mechanism in highly conductive amorphous carbon nitride thin films

G. Lazar, K. Zellama, M. Clin, and C. Godet

Appl. Phys. Lett. 85, 6176 (2004); http://dx.doi.org/10.1063/1.1839649 (3 pages) | Cited 10 times

Online Publication Date: 15 December 2004

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Nitrogenated amorphous carbon (a-C:N) films have been synthesized by radio frequency (rf) magnetron sputtering at various substrate temperatures and rf discharge powers. The temperature dependence of the electrical conductivity has been measured in order to identify the dominant conduction mechanism. The conductivity was found to increase over ten orders of magnitude with increasing growth temperature and discharge power. In the ohmic regime, the conductivity of the investigated a-C:N films is likely dominated by hopping conduction, in good agreement with a model for hopping in localized bandtail states, rather than by extended states band conduction.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Cd Deposition by sputtering
73.61.Ng Insulators
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth
73.20.At Surface states, band structure, electron density of states
71.55.Jv Disordered structures; amorphous and glassy solids

Atomic strings of group IV, III–V, and II–VI elements

S. Tongay, E. Durgun, and S. Ciraci

Appl. Phys. Lett. 85, 6179 (2004); http://dx.doi.org/10.1063/1.1839647 (3 pages) | Cited 12 times

Online Publication Date: 15 December 2004

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A systematic first-principles study of atomic strings made by group IV, III–V, and II–VI elements has revealed interesting mechanical, electronic, and transport properties. The double bond structure underlies their unusual properties. We found that linear chain of C, Si, Ge, SiGe, GaAs, InSb, and CdTe are stable and good conductor, although their parent diamond (zincblende) crystals are covalent (polar) semiconductors but, compounds SiC, BN, AlP, and ZnSe are semiconductors. First row elements do not form zigzag structures.
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71.20.Mq Elemental semiconductors
71.20.Nr Semiconductor compounds
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.15.Nc Total energy and cohesive energy calculations

Effects of n-type 4H-SiC epitaxial wafer quality on reliability of thermal oxides

Junji Senzaki, Kazutoshi Kojima, and Kenji Fukuda

Appl. Phys. Lett. 85, 6182 (2004); http://dx.doi.org/10.1063/1.1839279 (3 pages) | Cited 5 times

Online Publication Date: 15 December 2004

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The reliability of thermal oxides was investigated on n-type 4H-SiC(0001) epitaxial wafers with different metal impurity concentrations and surface roughness. Time-zero dielectric breakdown measurements showed that almost all of the thermal oxides ruptured at a field-to-breakdown (EBD) of 10 MV∕cm, and that the maximum EBD was 11 MV∕cm, despite the influence of the epitaxial wafer. On the other hand, time-dependent dielectric breakdown measurements indicated that the charge-to-breakdown (QBD) of the thermal oxides was influenced by the epitaxial wafer. This suggests that two types of oxide breakdown regimes exist under a high-stress field: one resulting from wafer influences, and the other intrinsic.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.22.Jp Dielectric breakdown and space-charge effects

The influence of the time-of-flight mobility on the efficiency of solid-state dye-sensitized TiO2 solar cells

C. Jäger, D. Haarer, B. Peng, and M. Thelakkat

Appl. Phys. Lett. 85, 6185 (2004); http://dx.doi.org/10.1063/1.1834717 (3 pages) | Cited 7 times

Online Publication Date: 15 December 2004

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The dependence of zero field charge carrier mobilities obtained from time-of-flight (TOF) measurements for a series of doped triphenyldiamines on trap depth and concentration were determined. The influence of these mobilities on the solar cell characteristics have been studied by measuring I–V characteristics and IPCE values using the same doped hole conductors in solid-state dye-sensitized TiO2 solar cells. The traps exhibit only a weak influence on the solar cell characteristics, because the traps which are responsible for low charge transport mobilities in the TOF experiment are filled under steady state illumination conditions. In consequence the effective mobility is raised almost to that of the pristine hole conductor, thus allowing the use of doped hole conductor systems in solar cells without any adverse effects.
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84.60.Jt Photoelectric conversion
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.20.Jq Electro-optical effects
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals

Drive current enhancement in p-type metal–oxide–semiconductor field-effect transistors under shear uniaxial stress

L. Shifren, X. Wang, P. Matagne, B. Obradovic, C. Auth, S. Cea, T. Ghani, J. He, T. Hoffman, R. Kotlyar, Z. Ma, K. Mistry, R. Nagisetty, R. Shaheed, M. Stettler, et al.

Appl. Phys. Lett. 85, 6188 (2004); http://dx.doi.org/10.1063/1.1841452 (3 pages) | Cited 10 times

Online Publication Date: 15 December 2004

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Recent attention has been given to metal–oxide–semiconductor field-effect transistor (MOSFET) device designs that utilize stress to achieve performance gain in both n-type MOSFETs (NMOS) and p-type MOSFETs (PMOS). The physics behind NMOS gain is better understood than that of PMOS gain, which has received less attention. In this letter, we describe the warping phenomena which is responsible for the gain seen in [110] uniaxially stressed PMOS devices on [100] orientated wafers. We also demonstrate that shear uniaxial stress in PMOS is better suited to MOSFET applications than biaxial stress as it is able to maintain gain at high vertical and lateral fields.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Low-resistivity and transparent indium-oxide-doped ZnO ohmic contact to p-type GaN

Jae-Hong Lim, Dae-Kue Hwang, Hyun-Sik Kim, Jin-Yong Oh, Jin-Ho Yang, R. Navamathavan, and Seong-Ju Park

Appl. Phys. Lett. 85, 6191 (2004); http://dx.doi.org/10.1063/1.1826231 (3 pages) | Cited 25 times

Online Publication Date: 15 December 2004

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We report on the indium-oxide-doped ZnO (IZO) transparent ohmic contact to the p‐GaN. The IZO transparent ohmic contact layer was deposited on p‐GaN by e-beam evaporation. The transmittance of an IZO film with a thickness of 250 nm was 84%–92% for the light in the wavelength range of 400 and 600 nm. In addition, the IZO contact film yielded a low specific contact resistance of 3.4×10−4 Ω cm2 on p‐GaN when annealed at 600 °C for 5 min under a nitrogen ambient. Auger electron spectroscopy and x-ray photoemission spectroscopy analyses of the IZO and p‐GaN interface indicated that Ga atoms had out-diffused and an InN phase was formed at the interface region after the thermal annealing process, resulting in a decrease in contact resistance. The light output power of a light-emitting diode (LED) with an IZO ohmic contact layer was increased by 34% at 83 mW of electrical input power compared to that of a LED with a Ni∕Au ohmic contact layer.
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85.60.Jb Light-emitting devices
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
73.61.Ey III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.40.Cg Contact resistance, contact potential
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
79.60.Jv Interfaces; heterostructures; nanostructures

Current-induced electroresistive effect in mixed-phase La0.67Ca0.33MnO3 thin films

A. Masuno, T. Terashima, Y. Shimakawa, and M. Takano

Appl. Phys. Lett. 85, 6194 (2004); http://dx.doi.org/10.1063/1.1840114 (3 pages) | Cited 11 times

Online Publication Date: 15 December 2004

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We examined electroresistive effects of epitaxial thin films of La0.67Ca0.33MnO3 deposited on LaAlO3(100) substrates. To be noted here is that these oxides are considerably lattice-mismatched. Measurements of the resistivity, magnetoresistance effect, and current-voltage characteristics of these films revealed that they were inhomogeneous and composed of domains of the highly strained charge-ordered insulator (COI) and the less strained ferromagnetic metal (FMM). By using a microfabricating process, we obtained high current densities and observed a current-induced irreversible behavior at low temperature. The irreversibility became larger with increasing current density. Below the insulator-metal (ferromagnetic) transition temperature, spin-polarized electrons in the FMM domains were injected into the neighboring COI domains. There they forced antiferromagnetically ordered spins to align parallel, leading to a current-induced first-order transition from the COI to the FMM.
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75.47.Lx Magnetic oxides
75.50.Dd Nonmetallic ferromagnetic materials
71.45.-d Collective effects
75.70.Ak Magnetic properties of monolayers and thin films
71.30.+h Metal-insulator transitions and other electronic transitions
72.25.-b Spin polarized transport
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