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5 Dec 2005

Volume 87, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 87, 234101 (2005); http://dx.doi.org/10.1063/1.2140082 (3 pages)

Ben McMillen, Chuck Jewart, Michael Buric, Kevin P. Chen, Yuankun Lin, and Wei Xu
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First-principles calculation of free Si(100) surface impurity enrichment

Scott A. Centoni, Babak Sadigh, George H. Gilmer, Tomás Díaz de la Rubia, and Charles B. Musgrave

Appl. Phys. Lett. 87, 232101 (2005); http://dx.doi.org/10.1063/1.2138811 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2005

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Low-temperature crystal growth techniques can deposit silicon films with impurity concentration orders of magnitude above their bulk solubility limits. First-principles calculations were performed of the energies (relative to the bulk) of single substitutional carbon, germanium, boron, and arsenic atoms at several positions within a thin (100) slab of silicon reconstructed as c(4×2). The energies of these impurities were found to be at least 0.2 eV lower than in the bulk, corresponding to surface enrichments of 1000 or greater at a temperature of 500 °C. General trends can be explained using the concepts of hybridization energy and lone pairs. The large surface reconstruction strain gives rise to this complex potential energy surface, and favors long-ranged order among impurities near the surface. As a result, we expect a complex dependence of trapped impurity concentrations on growth rate and temperature, with a high sensitivity to these parameters when the exchange rate of the impurity with neigboring sites is comparable to the monolayer deposition rate.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Md Surface thermodynamics, surface energies
61.72.S- Impurities in crystals

Measurements of thermally induced nanometer-scale diffusion depth of Pt/Ti/Pt/Au gate metallization on InAlAs/InGaAs high-electron-mobility transistors

Seiyon Kim, Ilesanmi Adesida, and Heedon Hwang

Appl. Phys. Lett. 87, 232102 (2005); http://dx.doi.org/10.1063/1.2137687 (3 pages) | Cited 8 times

Online Publication Date: 28 November 2005

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Platinum diffusion in InAlAs was investigated utilizing a Pt/Ti/Pt/Au gate contact on an In0.52Al0.48As/In0.53Ga0.47As/InP high-electron-mobility transistor (HEMT) structure. Capacitance-voltage measurements on large gate field-effect transistors and high-resolution cross-sectional transmission electron microscopy enabled the measurement of Pt diffusion depth with nanometer-scale accuracy. A continuous increase in Pt diffusion depth was observed at an annealing temperature of 250 °C with increasing time. After a 40 min anneal, a diffusion depth of 8 nm was measured. Such a deep Pt diffusion in a HEMT structure not only changes device parameters but also constitutes a serious reliability problem during device operation.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.Tv Field effect devices
68.37.Lp Transmission electron microscopy (TEM)

Quantum well behavior of single stacking fault 3C inclusions in 4H-SiC p-i-n diodes studied by ballistic electron emission microscopy

K.-B. Park, J. P. Pelz, J. Grim, and M. Skowronski

Appl. Phys. Lett. 87, 232103 (2005); http://dx.doi.org/10.1063/1.2138442 (3 pages) | Cited 8 times

Online Publication Date: 28 November 2005

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We show that “single” stacking fault 3C inclusions formed in 4H-SiC p-i-n diodes behave as electron quantum wells (QWs) with the QW energy depth of ∼ 0.25 eV below 4H-SiC conduction band minimum, by measuring the Schottky barriers on and away from inclusions with ballistic electron emission microscopy (BEEM). The Schottky barrier on the 4H area ([11-20] oriented) is measured to be essentially the same as (0001) plane studied previously, indicating that the interface pinning effects on both crystal faces are almost identical. Additionally, BEEM current amplitude is observed to be very sensitive to subsurface damage induced by polishing.
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85.30.Kk Junction diodes
68.37.Vj Field emission and field-ion microscopy
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.30.+y Surface double layers, Schottky barriers, and work functions

Deep-level characterization of N-doped ZnO films prepared by reactive magnetron sputtering

Yoshitaka Nakano, Takeshi Morikawa, Takeshi Ohwaki, and Yasunori Taga

Appl. Phys. Lett. 87, 232104 (2005); http://dx.doi.org/10.1063/1.2139852 (3 pages) | Cited 17 times

Online Publication Date: 29 November 2005

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We report on band gap states in N-doped ZnO (ZnO:N) films that were deposited on indium tin oxide/quartz substrates by reactive magnetron sputtering. Colored ZnO:N samples showed enhanced polycrystalline with increasing N-doping concentration, as determined by x-ray diffraction patterns. Deep-level optical spectroscopy measurements revealed three characteristic deep levels located at ∼ 0.98, ∼ 1.20, and ∼ 2.21 eV below the conduction band. In particular, the pronounced 2.21 eV band is newly introduced by the N doping and behaves as part of the valence band, resulting in band gap narrowing of ZnO. Therefore, this deep level is probably one origin of visible-light sensitivity in ZnO:N.
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71.55.Gs II-VI semiconductors
73.20.At Surface states, band structure, electron density of states

Effect of thin iridium oxide on the formation of interface dipole in organic light-emitting diodes

Soo Young Kim and Jong-Lam Lee

Appl. Phys. Lett. 87, 232105 (2005); http://dx.doi.org/10.1063/1.2135874 (3 pages) | Cited 16 times

Online Publication Date: 29 November 2005

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The 4,4′-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl was in situ deposited on both iridium-oxide-coated indium-tin-oxide (IrOx–ITO) and O2-plasma-treated ITO (O2–ITO), and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. The dipole energies of both O2–ITO and IrOx–ITO were same with each other, −0.3 eV, meaning the formation of same amount of interface dipole. The secondary electron emission spectra revealed that the work function of IrOx–ITO is higher by 0.5 eV than that of O2–ITO, resulting in the decrease of the turn-on voltage via reduction of hole injection barrier.
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85.60.Jb Light-emitting devices
81.65.-b Surface treatments

Picosecond carrier dynamics in AlInGaN multiple quantum wells

S. A. Hashemizadeh, J.-P. R. Wells, P. Murzyn, J. Brown, B. D. Jones, T. Wang, P. J. Parbrook, A. M. Fox, D. J. Mowbray, and M. S. Skolnick

Appl. Phys. Lett. 87, 232106 (2005); http://dx.doi.org/10.1063/1.2137990 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2005

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We report on measurements of stimulated emission in AlInGaN multiquantum wells using ultrafast pump-probe spectroscopy. Low power photoluminescence (PL) of Al0.04In0.015Ga0.945N/Al0.12In0.01Ga0.87N multiquantum wells (MQW) yields a single MQW PL peak at 347.2 nm at 10 K. Wavelength degenerate pump-probe measurements show a single exponential decay at excitation densities below the stimulated emission threshold having a recombination decay constant of 160 ps at room temperature. At excitation densities greater than 50 μJ/cm2 a biexponential decay is observed, with a fast component (3.3 ps at Iexc = 690 μJ/cm2) attributed to accelerated relaxation due to stimulated emission. The fractional strength of this fast component indicates that up to 85% of the excited carriers relax via stimulated emission.
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78.67.De Quantum wells
78.45.+h Stimulated emission
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics

Quantum and transport lifetimes of two-dimensional electrons gas in AlGaN/GaN heterostructures

P. Lorenzini, Z. Bougrioua, A. Tiberj, R. Tauk, M. Azize, M. Sakowicz, K. Karpierz, and W. Knap

Appl. Phys. Lett. 87, 232107 (2005); http://dx.doi.org/10.1063/1.2140880 (3 pages) | Cited 8 times

Online Publication Date: 30 November 2005

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The transport and quantum lifetimes were respectively deduced from low-temperature mobility and Shubnikov–de Haas measurements as a function of carrier density in metal organic vapor phase epitaxy-grown AlGaN/GaN/sapphire heterostructures. We show experimentally that the lifetime ratio varies as a bell curve, qualitatively confirming a recent theoretical prediction. However the experimental ratio varied much less than was theoretically predicted: From 9 to 19 for carrier densities in 1–9×1012 cm−2 range. Moreover, we show the variation of quantum time with carrier density presents some discrepancy with the theoretical study. We also show that transport to quantum lifetime ratio cannot be used alone as a clear figure of merit from AlGaN/GaN heterojunctions.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Single-hole transistor in p-type GaAs/AlGaAs heterostructures

Boris Grbić, Renaud Leturcq, Klaus Ensslin, Dirk Reuter, and Andreas D. Wieck

Appl. Phys. Lett. 87, 232108 (2005); http://dx.doi.org/10.1063/1.2139994 (3 pages) | Cited 16 times

Online Publication Date: 30 November 2005

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A single-hole transistor is patterned in a p-type, C-doped GaAs/AlGaAs heterostructure by scanning probe oxidation lithography. Clear Coulomb blockade resonances have been observed at Thole = 300 mK. A charging energy of ∼ 1.5 meV is extracted from Coulomb diamond measurements, in agreement with the lithographic dimensions of the dot. The absence of excited states in Coulomb diamond measurements, as well as the temperature dependence of Coulomb peak heights indicate that the dot is in the multilevel transport regime. Fluctuations in peak spacings larger than the estimated mean single-particle level spacing are observed.
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85.30.Tv Field effect devices
73.63.Kv Quantum dots
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.40.Hp Lithography, masks and pattern transfer
73.23.Hk Coulomb blockade; single-electron tunneling

Photocurrent-modulated optical nuclear polarization in bulk GaAs

Anant K. Paravastu, Patrick J. Coles, Jeffrey A. Reimer, Thaddeus D. Ladd, and Robert S. Maxwell

Appl. Phys. Lett. 87, 232109 (2005); http://dx.doi.org/10.1063/1.2140484 (3 pages) | Cited 7 times

Online Publication Date: 1 December 2005

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Application of a dc electric field to bulk, semi-insulating, GaAs during laser irradiation was observed to significantly affect optically pumped nuclear spin polarizations. Changes to nuclear polarizations correlated with nonlinear photoconductivity, and both depended significantly on excitation photon energy. Many aspects of the data could be explained by electric field-dependent population transfer between trapped and delocalized electronic spin reservoirs. These results indicate that semi-insulating GaAs could be a platform for localized optical and electric field control of nuclear spin polarization.
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72.40.+w Photoconduction and photovoltaic effects
76.60.-k Nuclear magnetic resonance and relaxation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
79.20.Ds Laser-beam impact phenomena

Experimental determination of electron and hole sublevels in modulation-doped InAs/GaAs quantum dots

Y. D. Jang, J. S. Yim, D. Lee, Gil-Ho Kim, C.-T. Liang, I. Farrer, and D. A. Ritchie

Appl. Phys. Lett. 87, 232110 (2005); http://dx.doi.org/10.1063/1.2140882 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2005

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Electron and hole sublevels in quantum dots (QDs) are experimentally determined using the excitation-power dependence of photoluminescence spectrum for a modulation-doped QD structure. The sublevel spacing between n = 1 and n = 2 electron states can be obtained from the photoluminescence (PL) spectrum under very low excitation and the spacing between n = 1 and n = 2 hole states can be obtained by comparing the PL spectrum under high excitation with the one under low excitation. The proposed method should give useful information in the design of QD devices, as well as for the verification of theoretical calculations of QD energy levels.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Short-channel polymer field-effect-transistor fabrication using spin-coating-induced edge template and ink-jet printing

S. P. Li, D. P. Chu, C. J. Newsome, D. M. Russell, T. Kugler, M. Ishida, and T. Shimoda

Appl. Phys. Lett. 87, 232111 (2005); http://dx.doi.org/10.1063/1.2140586 (3 pages) | Cited 12 times

Online Publication Date: 1 December 2005

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A method to fabricate polymer field-effect transistors with submicron channel lengths is described. A thin polymer film is spin coated on a prepatterned resist with a low resolution to create a thickness contrast in the overcoated polymer layer. After plasma and solvent etching, a submicron-sized line structure, which templates the contour of the prepattern, is obtained. A further lift-off process is applied to define source-drain electrodes of transistors. With a combination of ink-jet printing, transistors with channel length down to 400 nm have been fabricated by this method. We show that drive current density increases as expected, while the on/off current ratio 106 is achieved.
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85.30.Tv Field effect devices
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
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