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8 Nov 2004

Volume 85, Issue 19, pp. 4269-4539

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4343 (2004); http://dx.doi.org/10.1063/1.1814814 (3 pages)

H. Isshiki, M. J. A. de Dood, A. Polman, and T. Kimura
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Ballistic electron emission microscopy on spin valve structures

R. Heer, J. Smoliner, J. Bornemeier, and H. Brückl

Appl. Phys. Lett. 85, 4388 (2004); http://dx.doi.org/10.1063/1.1814423 (3 pages) | Cited 5 times

Online Publication Date: 8 November 2004

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Spin valve structures, as employed in base layers of spin valve transistor devices, are characterized by ballistic electron emission microscopy (BEEM). In detail, Co–Cu–Permalloy–Au layers sputtered onto n-type GaAs bulk substrates were studied. BEEM spectra taken on these multilayers show that magnetocurrents on the order of 600% can be achieved even at room temperature. Small area images (400 nm×400 nm) show that the spin filtering effect of the spin valves is quite homogeneous on the submicron scale. On larger scales, magnetic domains were imaged close to the switching field of the spin valve structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
68.37.Vj Field emission and field-ion microscopy

Improved characteristics for Au∕n‐GaSb Schottky contacts through the use of a nonaqueous sulfide-based passivation

Z. Y. Liu, D. A. Saulys, and T. F. Kuech

Appl. Phys. Lett. 85, 4391 (2004); http://dx.doi.org/10.1063/1.1815073 (3 pages) | Cited 6 times

Online Publication Date: 8 November 2004

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The influence of nonaqueous sulfide passivation (using Na2S in the inert solvent benzene) on Au∕n‐GaSb Schottky junction behavior was studied. The junction parameters, Schottky barrier height and ideality factor, were derived and compared with those of as-received GaSb surfaces as well as surfaces treated with aqueous sulfide solutions. The Schottky junction made on as-received GaSb is highly nonideal, while S-based passivation treatment of the GaSb surface before contact formation improves the rectifying behavior, and markedly reduces the reverse current. A benzene-based nonaqueous sulfide treatment results in GaSb surfaces with lower oxide and elemental antimony content than does the aqueous sulfide treatment. The produced Schottky barrier height increases to 0.61 eV and the Au∕n‐GaSb contact is close to an ideal Schottky junction.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Rv Passivation
73.40.Ns Metal-nonmetal contacts

Real-time detection of single-electron tunneling using a quantum point contact

L. M. K. Vandersypen, J. M. Elzerman, R. N. Schouten, L. H. Willems van Beveren, R. Hanson, and L. P. Kouwenhoven

Appl. Phys. Lett. 85, 4394 (2004); http://dx.doi.org/10.1063/1.1815041 (3 pages) | Cited 55 times

Online Publication Date: 8 November 2004

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We observe individual tunnel events of a single electron between a quantum dot and a reservoir, using a nearby quantum point contact (QPC) as a charge meter. The QPC is capacitively coupled to the dot, and the QPC conductance changes by about 1% if the number of electrons on the dot changes by one. The QPC is voltage biased and the current is monitored with a current–voltage (I–V) convertor at room temperature. We can resolve tunnel events separated by only 8 μs, limited by noise from the I–V convertor. Shot noise in the QPC sets a 25 ns lower bound on the accessible timescales.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena

Anomalous current–voltage characteristics and colossal electroresistance of amorphous carbon film on Si substrate

Q. Z. Xue, X. Zhang, P. Tian, and C. Jin

Appl. Phys. Lett. 85, 4397 (2004); http://dx.doi.org/10.1063/1.1814435 (3 pages) | Cited 9 times

Online Publication Date: 8 November 2004

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Amorphous carbon film (a-C film) was deposited on n-Si substrate by pulsed-laser deposition at room temperature. The electrical transport properties of a-C film/n-Si were investigated by current–voltage (I–V) measurements at various temperatures. The results indicate that the resistance of a-C film/n-Si is controlled by the applied electric current. The most important result is that when the value of the electric voltage is larger than a threshold, the current increases abruptly to a very large value, and the value of the voltage threshold decreases with increasing temperature. Correspondingly, the colossal electroresistance (ER) was achieved in the temperature range measured. The ER reaches −84.5% and −99.5% at T=310 K and 170 K, respectively. The mechanism of the I–V characteristics may be understood by an energy band structure of a-C film/n-Si. The anomalous I–V characteristics and colossal ER should be of interest for various applications such as field-effect devices.
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68.55.A- Nucleation and growth
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors
71.20.Mq Elemental semiconductors
81.15.Fg Pulsed laser ablation deposition

Influence of the dielectric roughness on the performance of pentacene transistors

Soeren Steudel, Stijn De Vusser, Stijn De Jonge, Dimitri Janssen, Stijn Verlaak, Jan Genoe, and Paul Heremans

Appl. Phys. Lett. 85, 4400 (2004); http://dx.doi.org/10.1063/1.1815042 (3 pages) | Cited 143 times

Online Publication Date: 8 November 2004

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The properties of the dielectric strongly influence the performance of organic thin-film transistors. In this letter, we show experimental results that quantify the influence of the roughness of the dielectric on the mobility of pentacene transistors and discuss the cause of it. We consider the movement of charge carriers out of the “roughness valleys” or across those valleys at the dielectric–semiconductor interface as the limiting step for the roughness-dependent mobility in the transistor channel.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Dn Low-field transport and mobility; piezoresistance
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.47.Fg Semiconductor surfaces

Greenish-white electroluminescence from p-type CuGaS2 heterojunction diodes using n-type ZnO as an electron injector

S. F. Chichibu, T. Ohmori, N. Shibata, T. Koyama, and T. Onuma

Appl. Phys. Lett. 85, 4403 (2004); http://dx.doi.org/10.1063/1.1818333 (3 pages) | Cited 17 times

Online Publication Date: 8 November 2004

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Greenish-white electroluminescence (EL) was observed from p-type (001) CuGaS2 chalcopyrite semiconductor epilayers grown on a (001) GaP substrate by metalorganic vapor phase epitaxy, due to the electron injection from preferentially (0001)-oriented polycrystalline n-type ZnO thin films deposited by the surface-damage-free helicon-wave-excited-plasma sputtering method. The structure was designed to enable the electron injection from n-type wide band gap partner forp‐CuGaS2 forming the ZnO∕CuGaS2 TYPE-I heterojunction. The EL spectra exhibited emission peaks and bands between 1.6 and 2.5 eV, although the higher energy portion was absorbed by the GaP substrate. Since the spectral line shape resembled that of the photoluminescence from the identical CuGaS2 epilayers, the EL was assigned to originate from p‐CuGaS2.
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85.60.Jb Light-emitting devices
78.66.Hf II-VI semiconductors
78.66.Li Other semiconductors
78.60.Fi Electroluminescence

Pentacene organic field-effect transistor on metal substrate with spin-coated smoothing layer

Yanbo Jin, Zhenlin Rang, Marshall I. Nathan, P. Paul Ruden, Christopher R. Newman, and C. Daniel Frisbie

Appl. Phys. Lett. 85, 4406 (2004); http://dx.doi.org/10.1063/1.1814802 (3 pages) | Cited 22 times

Online Publication Date: 8 November 2004

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In this letter we report the use of roughly polished aluminum substrates with spin-coated polymer-smoothing layers for the fabrication of pentacene field-effect transistors. Transistors with spin-coated poly(methylmethacrylate) gate insulator layers were fabricated and showed good performance. On the gate insulator surface, the root-mean-square roughness was found to be 0.18 nm, significantly smaller than the aluminum surface roughness, which is on the scale of tens of nanometers. Field-effect carrier mobilities extracted from the device data reached 0.75 cm2 V−1 s−1; the maximum on/off current ratio was near 5×106.
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85.30.Tv Field effect devices
73.61.Ph Polymers; organic compounds
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.A- Nucleation and growth

On the apparently anomalous response of porous silicon to nitrogen dioxide

G. Amato, L. Boarino, and F. Bellotti

Appl. Phys. Lett. 85, 4409 (2004); http://dx.doi.org/10.1063/1.1819517 (3 pages) | Cited 5 times

Online Publication Date: 8 November 2004

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Recent publications reported a large increase of conductivity in mesoporous silicon exposed to traces of nitrogen dioxide. The phenomenon has been studied from theoretical and experimental points of view. Even if a complete comprehension has not been reached yet, it seems clear that the simple increase in the number of mobile carriers inside the material cannot fully account for the experimental evidence; an increase of their mobility must provide a more robust contribution. The fresh observation of an opposite effect occurring in sufficiently thin mesoporous samples is then surprising. The present letter shows that such an apparently contradictory result can be explained in terms of the well-known theory of current injection in insulators.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.At Surface states, band structure, electron density of states
72.80.Cw Elemental semiconductors

Density of states determination from steady-state photocarrier grating measurements

J. A. Schmidt and C. Longeaud

Appl. Phys. Lett. 85, 4412 (2004); http://dx.doi.org/10.1063/1.1818732 (3 pages) | Cited 5 times

Online Publication Date: 8 November 2004

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We present a method to obtain the density of states (DOS) of photoconductive insulators based on steady-state photocarrier grating (SSPG) measurements. A simple expression—relating the DOS at the electron quasi-Fermi level to measurable quantities—is deduced by performing suitable approximations from the analytical solution of the generalized equations that describe the SSPG experiment. The validity of the approximations and the applicability of the final expression are verified from numerical simulations of the process. The usefulness of the method is demonstrated by performing measurements on a standard hydrogenated amorphous silicon sample.
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71.20.Mq Elemental semiconductors
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
72.40.+w Photoconduction and photovoltaic effects

GaAs Esaki junctions with autocompensated impurities in the n side by metalorganic chemical vapor deposition

Jizhi Zhang and Kei May Lau

Appl. Phys. Lett. 85, 4415 (2004); http://dx.doi.org/10.1063/1.1819996 (3 pages) | Cited 1 time

Online Publication Date: 8 November 2004

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GaAs Esaki junctions were grown at normal growth temperatures above 550 °C by low pressure metalorganic chemical vapor deposition. The n sides of these junctions were heavily doped with silane into the regime that impurities were autocompensated. Consequently, zero-bias tunnel resistance was significantly reduced. We obtained a low zero-bias specific tunnel resistance of 9.6×10−5 Ω cm2 with an optimized silane flow rate.
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73.40.Gk Tunneling
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.61.Ey III-V semiconductors
68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors

Energy-band alignments at ZrO2∕Si, SiGe, and Ge interfaces

S. J. Wang, A. C. H. Huan, Y. L. Foo, J. W. Chai, J. S. Pan, Q. Li, Y. F. Dong, Y. P. Feng, and C. K. Ong

Appl. Phys. Lett. 85, 4418 (2004); http://dx.doi.org/10.1063/1.1819988 (3 pages) | Cited 7 times

Online Publication Date: 8 November 2004

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The energy-band alignments for the ZrO2∕Si, ZrO2∕Si0.75Ge0.25, and ZrO2∕Ge interfaces have been studied using x-ray photoemission. The valence-band offsets of ZrO2∕Si, ZrO2∕Si0.75Ge0.25, and ZrO2∕Ge interfaces are determined to be 2.95, 3.13, and 3.36 eV, respectively, while the conduction-band offsets are found to be the same value of 1.76±0.03 eV for three interfaces. The upward shift of valence-band top accounts for the difference in the energy-band alignment at three interfaces.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films

Low-resistance and high-reflectance Ni∕Ag∕Ru∕Ni∕Au ohmic contact on p-type GaN

Ho Won Jang and Jong-Lam Lee

Appl. Phys. Lett. 85, 4421 (2004); http://dx.doi.org/10.1063/1.1819981 (3 pages) | Cited 11 times

Online Publication Date: 8 November 2004

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Show Abstract
We report a metallization scheme of low-resistance, high-reflectance, and thermally-stable ohmic contact on p-type GaN. The specific contact resistivity as low as 5.2×10−5 Ω cm2 and the high reflectance of 91% were simultaneously obtained from Ni (50 math)∕Ag (1200 math)∕Ru (500 math)∕Ni (200 math)∕Au (500 math) contact annealed at 500 °C in O2 ambient. The oxidation annealing promoted the outdiffusion of Ga atoms to dissolve in the Ag layer, leaving Ga vacancies below the contact. The Ru layer could act as a diffusion barrier for intermixing of the reflective Ag with upper layers of Ni and Au. Thus, suppression of the intermixing results in the high reflectance and good thermal stability of the contact.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation
61.72.J- Point defects and defect clusters
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
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