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13 Feb 2006

Volume 88, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 072905 (2006); http://dx.doi.org/10.1063/1.2172744 (3 pages)

Y. L. Li and L. Q. Chen
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Low erosion behavior of polystyrene films under erbium ion implantation

M. Bhattacharya, M. K. Sanyal, T. K. Chini, and P. Chakraborty

Appl. Phys. Lett. 88, 071902 (2006); http://dx.doi.org/10.1063/1.2168509 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2006

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Erbium ion implantation in polystyrene (PS) thin films has been performed with 40 and 60 keV ions to a dose range between 1×1014 and 1×1016 ions/cm2. The x-ray reflectivity technique was applied to determine the ion-induced eroded layer thickness and interestingly, the erosion rate is found to decrease with increasing ion doses exhibiting simple power law behavior of the form ∼ (dose)−b. We propose the formation of a carbonaceous network at the top surface, which seems to prevent further erosion of the polymer with increasing the duration of implantation time. These findings may open up a possibility of loading a large amount of erbium in a polymer matrix by the implantation technique to make it suitable for various optoelectronic applications.
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61.82.Pv Polymers, organic compounds
61.80.Jh Ion radiation effects
81.65.-b Surface treatments
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
61.72.S- Impurities in crystals

Evolution of wetting layer of InAs/GaAs quantum dots studied by reflectance difference spectroscopy

Y. H. Chen, J. Sun, P. Jin, Z. G. Wang, and Z. Yang

Appl. Phys. Lett. 88, 071903 (2006); http://dx.doi.org/10.1063/1.2175489 (3 pages) | Cited 12 times

Online Publication Date: 13 February 2006

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For the InAs/GaAs quantum-dot system, the evolution of the wetting layer (WL) with the InAs deposition thickness has been studied by reflectance difference spectroscopy (RDS) in combination with atomic force microscopy and photoluminescence. One transition related to the light hole in the WL has been observed clearly in RDS, from which its transition energy and in-plane optical anisotropy (OA) are determined. The evolution of WL with the InAs dot formation and ripening has been discussed. In addition, the remarkable changes in OA at the onsets of the dot formation and ripening have been observed, implying the mode transitions of atom transport between the WL and the dots.
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81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)

Structure and thermal stability of gold nanoplates

Caixia Kan, Guanghou Wang, Xiaoguang Zhu, Cuncheng Li, and Bingqiang Cao

Appl. Phys. Lett. 88, 071904 (2006); http://dx.doi.org/10.1063/1.2175500 (3 pages) | Cited 8 times

Online Publication Date: 13 February 2006

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Gold (Au) nanoplates with an average thickness of ∼ 70 nm and several 10 μm in edge size have been mass synthesized through a solution-phase method. Structural studies demonstrate that the Au nanoplates are single crystals with (111) planes as two basal surfaces. Fragmentation of Au nanoplates is found when temperature is higher than 450 °C. Investigations on the thermal stability of Au nanoplates suggest that the melting and breaking start mainly at the (110) bounded edges, while the (111) surfaces of Au nanoplates show high stability. This work is valuable for Au nanostructures applied at elevated temperatures.
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61.46.Hk Nanocrystals
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
64.70.D- Solid-liquid transitions
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Single [101]-oriented growth of La0.9Sr0.1MnO3 films on vicinal SrTiO3(001) substrates

M. J. Zhuo, Y. L. Zhu, X. L. Ma, and H. B. Lu

Appl. Phys. Lett. 88, 071905 (2006); http://dx.doi.org/10.1063/1.2172141 (3 pages) | Cited 7 times

Online Publication Date: 13 February 2006

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Thin films of orthorhombic La0.9Sr0.1MnO3, have been grown by computer-controlled laser molecular-beam epitaxy on SrTiO3(001) substrate and vicinal SrTiO3(001) substrates. Electron diffractions and high-resolution imaging reveal that the as-received thin films with thickness of 300 nm are epitaxially grown on the substrates. The microstructures in the film grown on SrTiO3(001) substrate are clarified in terms of the oriented microdomains, while the films on vicinal SrTiO3(001) substrates are predominated by a single [101]-oriented growth, which provides a useful routine for a design of preferred physical properties. Based on the minimization of surface energy, the mechanism of such a single domain formation is proposed.
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68.55.-a Thin film structure and morphology
68.60.-p Physical properties of thin films, nonelectronic
68.35.Md Surface thermodynamics, surface energies
75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides

Luminescence properties of highly Si-doped AlN

E. Monroy, J. Zenneck, G. Cherkashinin, O. Ambacher, M. Hermann, M. Stutzmann, and M. Eickhoff

Appl. Phys. Lett. 88, 071906 (2006); http://dx.doi.org/10.1063/1.2173622 (3 pages) | Cited 13 times

Online Publication Date: 13 February 2006

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We report on the optical characterization of highly Si-doped AlN layers grown by plasma-assisted molecular-beam epitaxy. Cathodoluminescence spectra reveal a sharp band-edge line and two broadbands around 4.4 eV and 3.6 eV. Near-band-edge luminescence remains intense at room temperature, and shows a systematic redshift with increasing Si concentration. Regarding the low-energy bands, we observe a redshift of the emission around 3.6 eV with increasing Si concentration accompanied by an increase in relative intensity compared to the 4.4 eV band.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.uj III-V and II-VI semiconductors

Growth and characterization of AlGaNP on GaP(100) substrates

V. A. Odnoblyudov and C. W. Tu

Appl. Phys. Lett. 88, 071907 (2006); http://dx.doi.org/10.1063/1.2173709 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2006

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We describe epitaxial growth of GaNP, AlNP, and AlGaNP with low nitrogen concentration (<5%) on GaP (100) substrates. Using a thermodynamic approach, we explain the difference between nitrogen incorporation into GaP and AlP. We demonstrate and explain peculiarities of AlGaNP quaternary alloy growth: Dependence of nitrogen concentration on Al composition and dependence of crystal quality on Al composition.
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81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
68.55.Nq Composition and phase identification

Study on in-plane optical anisotropy of Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice by reflectance difference spectroscopy

L. Zhao, Y. H. Zuo, W. H. Shi, Q. M. Wang, Y. H. Chen, and H. N. Wang

Appl. Phys. Lett. 88, 071908 (2006); http://dx.doi.org/10.1063/1.2172223 (3 pages) | Cited 1 time

Online Publication Date: 13 February 2006

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Si0.75Ge0.25/Si/Si0.5Ge0.5 trilayer asymmetric superlattices were prepared on Si (001) substrate by ultrahigh vacuum chemical vapor deposition at 500 °C. The nonlinear optical response caused by inherent asymmetric interfaces in this structure predicted by theories was verified by in-plane optical anisotropy in (001) plane measured via reflectance difference spectroscopy. The results show Si0.75Ge0.25/Si/Si0.5Ge0.5 asymmetric superlattice is optically biaxial and the two optical eigen axes in (001) plane are along the directions [110] and [−110], respectively. Reflectance difference response between the above two eigen axes can be influenced by the width of the trilayers and reaches as large as ∼ 10−4–10−3 in 15-period 2.7 nm‐Si0.75Ge0.25/8 nm‐Si/1.3 nm‐Si0.5Ge0.5 superlattice when the normal incident light wavelength is in the range of 500–1100 nm, which is quite remarkable because the optical anisotropy does not exist in bulk Si.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Effect of perforated transparent electrodes on light transmittance and light scattering in substrates used for microcrystalline silicon thin-film solar cells

Yoshiyuki Nasuno, Noriyoshi Kohama, Kazuhito Nishimura, Takashi Hayakawa, Hiroshi Taniguchi, and Masafumi Shimizu

Appl. Phys. Lett. 88, 071909 (2006); http://dx.doi.org/10.1063/1.2176857 (3 pages) | Cited 12 times

Online Publication Date: 14 February 2006

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The effect of a perforated transparent electrode, which is an electrode punctuated with holes, on light transmittance and light scattering was studied using textured ZnO:Ga formed by wet etching. The perforations were found to play a role not only in improving transmittance but also in maintaining high haze factor. The influence of the surface morphology of textured ZnO:Ga on the growth of hydrogenated microcrystalline silicon and on solar cell performance was also studied. It was found that, while the ZnO:Ga surface is not steep, a height difference is present on the substrate surface at the edge of the perforations. To resolve this problem, an additional thin ZnO:Ga layer was deposited on a substrate which already had a perforated transparent electrode. Improvements in solar cell performance were obtained while high open circuit voltage and high fill factor were maintained.
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84.60.Jt Photoelectric conversion
81.65.Cf Surface cleaning, etching, patterning

Measurement of residual stresses in micromachined structures in a microregion

N. Sabaté, D. Vogel, A. Gollhardt, J. Keller, B. Michel, C. Cané, I. Gràcia, and J. R. Morante

Appl. Phys. Lett. 88, 071910 (2006); http://dx.doi.org/10.1063/1.2177357 (3 pages) | Cited 8 times

Online Publication Date: 14 February 2006

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The use of a focused ion beam equipment is reported to find out the in-plane residual stress value of a microelectromechanical system structure by performing a local stress release. The ion beam column is used to mill stress-release slots of a few microns, whereas the scanning electron column captures micrographs of the milled area before and after the stress release process. The displacement component perpendicular to the slot is obtained from digital image correlation analysis of the captured high-resolution micrographs. The fitting of the experimental results with an analytical model together with the independent determination of the Young’s modulus allows one to find the residual stress value of the layer under study to a very good accuracy.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
46.25.-y Static elasticity

Giant enhanced optical nonlinearity of colloidal nanocrystals with a graded-index host

J. J. Xiao and K. W. Yu

Appl. Phys. Lett. 88, 071911 (2006); http://dx.doi.org/10.1063/1.2175484 (3 pages)

Online Publication Date: 14 February 2006

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The effective linear and third-order nonlinear optical properties of metallic colloidal crystal immersed in a graded-index host fluid are investigated theoretically. The local electric fields are extracted self-consistently based on the layer-to-layer interactions, which are readily given by the Lekner summation method. The resultant optical absorption and nonlinearity enhancement show a series of sharp peaks, which merge in a broadened resonant band. The sharp peaks become a continuous band for increasing packing density and number of layers. We believe that the sharp peaks arise from the in-plane dipolar interactions and the surface plasmon resonance, whereas the continuous band is due to the presence of the gradient in the host refractive index. These results have not been observed in homogeneous and randomly dispersed colloids, and thus would be of great interest in optical nanomaterial engineering.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.-k Nonlinear optics
42.70.Mp Nonlinear optical crystals
82.70.Dd Colloids
73.22.Lp Collective excitations
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Enhanced parametric processes in binary metamaterials

Maxim V. Gorkunov, Ilya V. Shadrivov, and Yuri S. Kivshar

Appl. Phys. Lett. 88, 071912 (2006); http://dx.doi.org/10.1063/1.2168755 (3 pages) | Cited 15 times

Online Publication Date: 14 February 2006

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We suggest double-resonant (binary) metamaterials composed of two types of magnetic resonant elements, and demonstrate that in the nonlinear regime such metamaterials provide unique possibilities for phase-matched parametric interaction and enhanced second-harmonic generation.
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42.70.Mp Nonlinear optical crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Low-temperature solvothermal route to 2H–SiC nanoflakes

Guifu Zou, Chao Dong, Kan Xiong, Hui Li, Changlong Jiang, and Yitai Qian

Appl. Phys. Lett. 88, 071913 (2006); http://dx.doi.org/10.1063/1.2174123 (3 pages) | Cited 15 times

Online Publication Date: 15 February 2006

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Silicon carbide nanoflakes have been synthesized through a one-step solvothermal route involving reaction of SiCl4 and CaC2 at 180 °C for the first time. According to x-ray powder diffraction, infrared, and Raman spectra analysis, the obtained nanoflakes possess a crystalline structure of 2H–SiC. Electron microscopy investigations show that the nanoflakes have typical diameters of 200–500 nm, thickness of ∼ 15 nm, and grow along the [001] direction. The nanoflakes exhibit a new photoluminescence peak at ∼ 314 nm, which is ascribed to defects in the SiOx. The possible growth mechanism of the nanoflakes is discussed.
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81.07.Bc Nanocrystalline materials
81.05.Hd Other semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials

Length-scale dependence of the step bunch self-organization on patterned vicinal Si(111) surfaces

T. Kwon, R. J. Phaneuf, and H.-C. Kan

Appl. Phys. Lett. 88, 071914 (2006); http://dx.doi.org/10.1063/1.2175501 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2006

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We use lithographic patterning and high-temperature annealing to investigate the length-scale dependence of self-organization of step bunches on vicinal Si(111) surfaces due to the motion and interference of misorientation-derived straight steps and the circular steps which bound cylindrical pits. Annealing of patterns with small pit diameters produces a rapid relaxation to straight step bunches, while larger structures maintain significant in-plane corrugations for as long as the out-of-plane corrugations persist. This indicates the existence of a characteristic length scale, set by the competition between the Gibbs–Thomson effect and sublimation. Significantly, the eventual relaxation is to nearly uniform step trains indicating that the late stage evolution is dominated by repulsive step-step interactions.
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68.47.Fg Semiconductor surfaces
81.16.Dn Self-assembly
81.16.Rf Micro- and nanoscale pattern formation
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
64.70.Hz Solid-vapor transitions

Real-time in situ growth study of TiN- and TiCxNy-based superhard nanocomposite coatings using spectroscopic ellipsometry

P. Jedrzejowski, A. Amassian, E. Bousser, J. E. Klemberg-Sapieha, and L. Martinu

Appl. Phys. Lett. 88, 071915 (2006); http://dx.doi.org/10.1063/1.2173719 (3 pages) | Cited 7 times

Online Publication Date: 15 February 2006

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We investigate in situ and in real-time the growth of superhard ternary nanocomposite (nc)-TiN∕amorphous (a)‐Si3N4 and quaternary nc‐TiCxNy/a‐SiCN films. Using nondestructive, noncontact spectroscopic ellipsometry and appropriate ellipsometric models, we determine the variation of optical constants, film resistivity, and electron scattering time and mean free path as a function of thickness and particle size. Based on the optical and electrical behavior, we propose a microstructural model of superhard nanocomposite films, postulating the interconnectivity between individual nanoparticles, presence of defects in the individual grains, and particle size varying in the initial stage of the film growth.
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68.55.-a Thin film structure and morphology
81.15.Aa Theory and models of film growth
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing

Large capacitance-voltage hysteresis loops in SiO2 films containing Ge nanocrystals produced by ion implantation and annealing

C. J. Park, K. H. Cho, W.-C. Yang, H. Y. Cho, Suk-Ho Choi, R. G. Elliman, J. H. Han, and Chungwoo Kim

Appl. Phys. Lett. 88, 071916 (2006); http://dx.doi.org/10.1063/1.2175495 (3 pages) | Cited 32 times

Online Publication Date: 16 February 2006

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Metal-oxide-semiconductor structures containing Ge nanocrystals (NCs) of 3–4 nm diameter and 2×1012 cm−2 density are shown to exhibit capacitance-voltage hysteresis of 20.9 V, one of the largest observed in Ge-NC based nonvolatile memories. The Ge NCs were fabricated in an oxide of 30 nm thickness by ion implantation with 30 keV Ge2− ions to an equivalent fluence of 1×1016 Ge cm−2 followed by annealing at 950 °C for 10 min. Secondary ion mass spectroscopy and transmission electron microscopy demonstrate the existence of Ge NCs whose average distance from the SiO2/Si interface is about 6.7 nm. It is shown that the memory effect is a likely consequence of charge trapping at Ge NCs and that it is enhanced by accurately controlling the distribution of Ge NCs with respect to the Si/SiO2 interface.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.46.Hk Nanocrystals
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Lp Transmission electron microscopy (TEM)

Degradation in photocatalytic activity induced by hydrogen-related defects in nano-LiNbO3 material

Zhaosheng Li, Tao Yu, Zhigang Zou, and Jinhua Ye

Appl. Phys. Lett. 88, 071917 (2006); http://dx.doi.org/10.1063/1.2175479 (3 pages) | Cited 16 times

Online Publication Date: 16 February 2006

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As a representative example, nano-LiNbO3 is prepared by a wet-chemical method in order to enhance its photocatalytic activity through improving the surface area. The samples perform good crystallinity from powder x-ray diffraction and transmission-electron-microscope observations. It is surprising that photocatalytic activity of nano-LiNbO3 decreases with an increase of its surface area. The presence of hydrogen in the as-prepared LiNbO3 samples is detected by measuring the OH− absorption that occurred near 3500 cm−1 in infrared spectra. Though the surface area of the nano-LiNbO3 samples with good crystallinity increases with a decrease of the sintered temperature, the number of hydrogen-related defects in the samples increases noticeably, thus reducing the photocatalytic activities of the nano-LiNbO3 samples.
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81.07.Bc Nanocrystalline materials
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Variable-angle ellipsometry and molecular orientation in monoclinic organic semiconductors

S. Tavazzi and M. Campione

Appl. Phys. Lett. 88, 071918 (2006); http://dx.doi.org/10.1063/1.2173254 (3 pages) | Cited 5 times

Online Publication Date: 16 February 2006

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Variable-angle ellipsometry has been used to characterize oligothiophene crystals with principal axes inclined at an angle to the surface normal. The results allow deducing with high sensitivity the orientation of the molecules in these anisotropic and absorbing organic solids, thus allowing one to follow the evolution of the molecular orientation after inducing the transition of the crystallographic structure between the two polymorphs of quaterthiophene. This material is representative of a large class of solids with technological applications in either crystal or thin-film form, where different structural properties and molecular orientation may arise from different preparation conditions.
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61.66.Hq Organic compounds
33.15.Bh General molecular conformation and symmetry; stereochemistry
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Effects of excitonic diffusion on stimulated emission in nanocrystalline ZnO

Ger Tobin, Enda McGlynn, Martin O. Henry, Jean-Paul Mosnier, Eduardo de Posada, and James G. Lunney

Appl. Phys. Lett. 88, 071919 (2006); http://dx.doi.org/10.1063/1.2174107 (3 pages) | Cited 9 times

Online Publication Date: 17 February 2006

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We present optically pumped emission data for ZnO, showing that high excitation effects and stimulated emission/lasing are observed in nanocrystalline ZnO thin films at room temperature, although such effects are not seen in bulk material of better optical quality. A simple model of exciton density profiles is developed which explains our results and those of other authors. Inhibition of exciton diffusion in nanocrystalline samples compared to bulk significantly increases exciton densities in the former, leading—via the nonlinear dependence of emission in the exciton bands on the pump intensity—to large increases in emission and to stimulated emission.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
78.45.+h Stimulated emission

Electronic characterization and effects of light-induced degradation on hydrogenated nanocrystalline silicon

Adam F. Halverson, James J. Gutierrez, J. David Cohen, Baojie Yan, Jeffrey Yang, and Subhendu Guha

Appl. Phys. Lett. 88, 071920 (2006); http://dx.doi.org/10.1063/1.2175480 (3 pages) | Cited 5 times

Online Publication Date: 17 February 2006

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Hydrogenated nanocrystalline silicon was characterized using the transient photocapacitance (TPC) method. The TPC spectra show these materials to have a mixed-phase nature. At low temperatures, the spectra appeared very microcrystalline, whereas at moderate temperatures they appeared very similar to those for hydrogenated amorphous silicon. These differences are shown to result from the temperature dependence of the minority carrier collection from the nanocrystalline component. The effects of light-induced degradation were also studied. This caused a substantial decrease in minority carrier collection, similar to lowering the temperature of the undegraded sample. However, no concomitant increase in dangling bond defect density was observed.
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72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials

Experimental study of LO phonons and excitons in ZnO nanoparticles produced by room-temperature organometallic synthesis

F. Demangeot, V. Paillard, P. M. Chassaing, C. Pagès, M. L. Kahn, A. Maisonnat, and B. Chaudret

Appl. Phys. Lett. 88, 071921 (2006); http://dx.doi.org/10.1063/1.2177545 (3 pages) | Cited 24 times

Online Publication Date: 17 February 2006

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We report here the study by optical microspectroscopy of crystalline ZnO nanoparticles produced by room-temperature organometallic synthesis. We present resonant Raman scattering spectrum obtained from different sized nanostructures from which the longitudinal-optical (LO) phonon frequency has been found to be very weakly dependent on their size. Low-temperature photoluminescence measurements reveal that (i) the band-edge PL of ZnO nanoparticles is dominated by weakly bound localized exciton, and that (ii) its energy does not exhibit any spatial confinement effect. These results enlighten the need for surface passivation of the nanoparticles to improve their UV emission potential.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.35.-y Excitons and related phenomena
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Ab initio calculated binodal and spinodal of cubic Ti1−xAlxN

P. H. Mayrhofer, D. Music, and J. M. Schneider

Appl. Phys. Lett. 88, 071922 (2006); http://dx.doi.org/10.1063/1.2177630 (3 pages) | Cited 32 times

Online Publication Date: 17 February 2006

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During annealing, metastable NaCl-structured (c) Ti1−xAlxN films initially exhibit spinodal decomposition which results in age hardening. Based on ab initio calculations, we show that the chemical requirement for spinodal decomposition in the quasibinary c‐TiN–c‐AlN system is fulfilled over a wide composition and temperature range. The enthalpy change for the decomposition of c‐Ti0.34Al0.66N is ∼ 26.4 kJ mol−1, which is in good agreement with previously reported experiments. The obtained results enable materials design of Ti1−xAlxN-based coating systems for high-temperature applications.
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64.75.-g Phase equilibria
81.40.Gh Other heat and thermomechanical treatments
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
65.40.G- Other thermodynamical quantities
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Low-voltage and high-field-effect mobility organic transistors with a polymer insulator

Yunseok Jang, Do Hwan Kim, Yeong Don Park, Jeong Ho Cho, Minkyu Hwang, and Kilwon Cho

Appl. Phys. Lett. 88, 072101 (2006); http://dx.doi.org/10.1063/1.2173633 (3 pages) | Cited 53 times

Online Publication Date: 13 February 2006

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A key issue in research into organic thin-film transistors (OTFTs) is low-voltage operation. In this study, we fabricated a pentacene thin-film transistor with an ultrathin layer of polyvinyl alcohol (9 nm) as a gate insulator, and obtained a device with excellent electrical characteristics at low operating voltages (below 2 V). This device was found to have a field-effect mobility of 1.1 cm2/V s, a threshold voltage of −0.98 V, an exceptionally low subthreshold slope of 180 mV/decade, and an on/off current ratio of 106. This favorable combination of properties means that such OTFTs can be operated successfully at voltages below 2 V.
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85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Current crowding-induced electromigration in SnAg3.0Cu0.5 microbumps

Kuo Ning Chiang, Chien Chen Lee, Chang Chun Lee, and Kuo Ming Chen

Appl. Phys. Lett. 88, 072102 (2006); http://dx.doi.org/10.1063/1.2173710 (3 pages) | Cited 18 times

Online Publication Date: 13 February 2006

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To determine the relevance of current crowding to electromigration in the SnAg3.0Cu0.5 solder bump, a three-dimensional dual bumps simulation model was designed to demonstrate how current crowding can enhance the local atomic flux along the electron flow path. The finding of void formation occurred at the entrance points to the cathode sides and the enhancement of the growth and clustering of the intermetallic compound at the outgoing points of the anode sides along the electron flow path were verified experimentally. The tilting effect is obvious at the anode/chip side. The experimental mean-time-to-failure was observed, and Black’s equation with Joule heating effect were investigated as well.
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66.30.Qa Electromigration
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Fabrication and characterization of vertical-type double-gate metal-oxide-semiconductor field-effect transistor with ultrathin Si channel and self-aligned source and drain

Meishoku Masahara, Yongxun Liu, Kazuhiko Endo, Takashi Matsukawa, Kunihiro Sakamoto, Kenichi Ishii, Shinichi O’uchi, Etsuro Sugimata, Hiromi Yamauchi, and Eiichi Suzuki

Appl. Phys. Lett. 88, 072103 (2006); http://dx.doi.org/10.1063/1.2173715 (3 pages) | Cited 3 times

Online Publication Date: 13 February 2006

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A fabrication technique for a vertical double-gate metal-oxide-semiconductor field-effect transistor (DG MOSFET) with a standing-up ultrathin channel (UTC) and self-aligned source and drain (S/D) is proposed. A 20 nm thick vertical UTC with low channel thickness fluctuation was formed on a (110)-oriented Si substrate using orientation-dependent wet etching. The top and bottom S/D were self-aligned to the DGs by using a combination of ion implantation and solid-phase diffusion. The fabricated vertical DG MOSFETs revealed that the channel thickness less influences the threshold voltage. Furthermore, a low sub-threshold slope of 68.8 mV/decade was achieved with a channel thickness of 20 nm.
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85.30.Tv Field effect devices
81.65.Cf Surface cleaning, etching, patterning

Metalorganic chemical vapor deposition growth of high-quality InAs/GaSb type II superlattices on (001) GaAs substrates

X. B. Zhang, J. H. Ryou, R. D. Dupuis, A. Petschke, S. Mou, S. L. Chuang, C. Xu, and K. C. Hsieh

Appl. Phys. Lett. 88, 072104 (2006); http://dx.doi.org/10.1063/1.2168668 (3 pages) | Cited 12 times

Online Publication Date: 14 February 2006

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InAs layers and InAs/GaSb type II superlattices (SLs) were grown on (001) GaAs substrates by metalorganic chemical vapor deposition. A thin low-temperature GaSb nucleation layer and a thicker high-temperature metamorphic GaSb buffer layer were introduced before the growth of InAs or the SLs. By optimizing the growth temperature, the interface gas switching and the growth rate, morphology, and structural properties of the grown structures are significantly improved. In some cases, nanopipes are found in these structures. Morphology studies of the InAs heteroepitaxial layers show that (1) the diameter of these nanopipes decreases with the growth temperature; (2) nanopipes are nucleated from the interface of GaSb/InAs; and (3) the density of nanopipes depends on the passivation of GaSb surface before the growth of the InAs. In growing InAs/GaSb SLs, we show that the growth rate of GaSb has a strong effect on the morphology and that the unintentional interfacial InSb layer formed at the InAs/GaSb interfaces is the origin of the nanopipes. Through the optimization of the growth parameters, high-quality 100-period SLs without nanopipes and with good optical absorption in 3–8 μm infrared region have been realized.
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81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Rv Passivation
78.30.Fs III-V and II-VI semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
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