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18 Oct 2004

Volume 85, Issue 16, pp. 3343-3639

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 3570 (2004); http://dx.doi.org/10.1063/1.1807953 (2 pages)

X. N. Zhang, C. R. Li, Z. Zhang, and Z. X. Cao
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Sulfur passivation for shallow Pd∕W∕Au ohmic contacts to p-InGaSb

S. H. Wang, S. E. Mohney, J. A. Robinson, and B. R. Bennett

Appl. Phys. Lett. 85, 3471 (2004); http://dx.doi.org/10.1063/1.1807013 (3 pages) | Cited 8 times

Online Publication Date: 22 October 2004

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The relationship between the specific contact resistance of nonalloyed Pd∕W∕Au ohmic contacts to p-In0.25Ga0.75Sb and premetallization surface preparations is examined. The resistance of ohmic contacts is minimized when p-InGaSb is exposed briefly to a dilute (NH4)2S solution. This treatment minimizes the thickness of any residual oxide or sulfide layer on the semiconductor and avoids excessive etching of the semiconductor, which would make the contact less shallow. A specific contact resistance of 5.9×10−7 Ω cm2 is achieved for a Pd∕W∕Au (2∕50∕145 nm) contact that consumes no more than 5 nm of InGaSb.
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81.65.Rv Passivation
81.65.Cf Surface cleaning, etching, patterning
73.40.Cg Contact resistance, contact potential
81.05.Ea III-V semiconductors
73.40.Ns Metal-nonmetal contacts

Time-of-flight analysis of charge mobility in a Cu-phthalocyanine-based discotic liquid crystal semiconductor

Hideo Fujikake, Takeshi Murashige, Makiko Sugibayashi, and Kazuchika Ohta

Appl. Phys. Lett. 85, 3474 (2004); http://dx.doi.org/10.1063/1.1805178 (3 pages) | Cited 21 times

Online Publication Date: 22 October 2004

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We used a time-of-flight method to study the charge carrier mobility properties of a molecular-aligned discotic liquid crystal semiconductor based on Cu-phthalocyanine. The heated isotropic-phase semiconductor material was sandwiched between transparent electrodes coated onto glass substrates without conventional alignment layers. This was then cooled, and a discotic liquid crystal semiconductor cell was obtained, which we used to make mobility measurements. The material had a fixed molecular alignment due to the supercooling of the hexagonal columnar mesophase. It was clarified that the carrier mobility for electrons was as high as it was for holes at room temperature. The maximum value of negative charge mobility reached 2.60×10−3 cm2∕V s, although negative carrier mobility is often much lower than positive carrier mobility in other organic semiconductors, including conventional Cu-phthalocyanine vacuum-deposited films.
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73.61.Ph Polymers; organic compounds
61.30.-v Liquid crystals
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Integrated optical waveguides with liquid cores

D. Yin, D. W. Deamer, H. Schmidt, J. P. Barber, and A. R. Hawkins

Appl. Phys. Lett. 85, 3477 (2004); http://dx.doi.org/10.1063/1.1807966 (3 pages) | Cited 34 times

Online Publication Date: 22 October 2004

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We report the design, fabrication, and demonstration of single-mode integrated optical waveguides with liquid cores. The principle of the device is based on antiresonant reflecting optical (ARROW) waveguides with hollow cores. We describe design principles for waveguide loss optimization down to 0.1∕cm. Using a fabrication process based on conventional silicon microfabrication and sacrificial core layers, waveguides of varying widths and lengths with volumes covering the pico- to nanoliter range were fabricated. We observe confined mode propagation, measure waveguide losses of 2.4∕cm, and demonstrate that the waveguides possess tailorable wavelength selectivity. The potential for highly integrated, sensitive devices based on these properties of the ARROW waveguides is discussed.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.25.Bs Wave propagation, transmission and absorption

Effects of exciton–biexciton coherent coupling on exciton absorption in quantum dots

Hideki Gotoh, Hidehiko Kamada, Tadashi Saitoh, Hiroaki Ando, and Jiro Temmyo

Appl. Phys. Lett. 85, 3480 (2004); http://dx.doi.org/10.1063/1.1807949 (3 pages) | Cited 1 time

Online Publication Date: 22 October 2004

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We report unusual excitonic absorption spectra with dip-shaped structures caused by exciton–biexciton coherent interactions in quantum dots. The exciton absorption spectrum is measured with the micro-photoluminescence excitation technique in a single InGaAs quantum dot. The spectrum changes from Lorenztian-shaped to dip-shaped with increasing excitation intensity. A theoretical analysis with the density matrix method reveals that exciton–biexciton coherent interactions create dressed states in the exciton–biexciton system and lead to the unusual absorption spectra.
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73.21.La Quantum dots
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds

Ultra-low-frequency self-oscillation of photocurrent in InxGa1−xAs∕Al0.15Ga0.85As multiple-quantum-well p–i–n diodes

A. Satake, K. Tanigawa, T. Kimura, K. Fujiwara, and N. Sano

Appl. Phys. Lett. 85, 3483 (2004); http://dx.doi.org/10.1063/1.1806268 (3 pages)

Online Publication Date: 22 October 2004

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We report an observation of ultra-low-frequency self-oscillation of photocurrent in InxGa1−xAs∕Al0.15Ga0.85As multiple-quantum-well p–i–n diodes. The photocurrent intensity shows self-oscillations with a characteristic frequency of ∼0.1 Hz at low temperatures under reverse bias voltages. The photocurrent self-oscillation depends on applied bias voltage, temperature, illumination power, and indium content of quantum-well layers. These dependences indicate that the photocurrent self-oscillation is attributed to photogenerated carriers trapped in localized centers within InxGa1−xAs quantum-well regions.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Kk Junction diodes
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces

A potential low-temperature oxide-ion conductor: La2−xBaxMo2O9

S. Basu, P. Sujatha Devi, and H. S. Maiti

Appl. Phys. Lett. 85, 3486 (2004); http://dx.doi.org/10.1063/1.1808505 (3 pages) | Cited 25 times

Online Publication Date: 22 October 2004

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An oxide ion conducting material, La1.94Ba0.06Mo2O9, with ionic conductivity of the order of 0.084 S∕cm at 800 °C in air was prepared by a citrate-nitrate auto-ignition process. A 3% Ba doping has suppressed the resistive transition of unsubstituted La2Mo2O9, which in turn stabilized the high-temperature cubic phase at room temperature as confirmed from x-ray diffraction, differential thermal analysis, and dilatometric studies. Impedance measurements on sintered La1.94Ba0.06Mo2O9 further lend strong support that a small amount of Ba doping has increased the overall conductivity of the parent compound La2Mo2O9 to a notable extent both at low and high temperatures.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
66.30.H- Self-diffusion and ionic conduction in nonmetals
65.40.De Thermal expansion; thermomechanical effects
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Optical properties of AlN and GaN in elevated temperatures

K. B. Nam, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 85, 3489 (2004); http://dx.doi.org/10.1063/1.1806545 (3 pages) | Cited 15 times

Online Publication Date: 22 October 2004

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Deep ultraviolet photoluminescence spectroscopy has been employed to study the optical transitions in AlN and GaN epilayers at temperatures from 10 to 800 K, from which the parameters that describe the temperature variation of the energy band gap (α and β or aB and θ) and linewidth broadening have been obtained. These parameters are compared with the previously reported values in AlN and GaN obtained by different methods in narrower temperature ranges. Our experimental results demonstrate that the broader temperature range of measurements is necessary to obtain accurate values of these parameters, particularly for AlN. These results, together with other well-known physical properties of AlN, may expand future prospects for the application of III-nitride materials.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Spin injection from Fe3Si into GaAs

A. Kawaharazuka, M. Ramsteiner, J. Herfort, H.-P. Schönherr, H. Kostial, and K. H. Ploog

Appl. Phys. Lett. 85, 3492 (2004); http://dx.doi.org/10.1063/1.1807014 (3 pages) | Cited 31 times

Online Publication Date: 22 October 2004

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We demonstrate room-temperature spin injection from the epitaxially grown ferromagnetic metal Fe3Si into the semiconductor GaAs. The injection efficiency is comparable to values previously obtained for the Fe∕GaAs and MnAs∕GaAs hybrid systems using the emission of similar (In,Ga)As∕GaAs light-emitting diodes for the detection of spin polarization. The temperature dependence of the detected polarization is explained by taking into account spin relaxation inside the semiconductor device.
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85.60.Jb Light-emitting devices
72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth

Graphitic features on SiC surface following oxidation and etching using surface enhanced Raman spectroscopy

Weijie Lu, L. C. Feldman, Y. Song, S. Dhar, W. E. Collins, W. C. Mitchel, and J. R. Williams

Appl. Phys. Lett. 85, 3495 (2004); http://dx.doi.org/10.1063/1.1804610 (3 pages) | Cited 18 times

Online Publication Date: 22 October 2004

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Graphitic features are detected on 4H-SiC surface following oxidation and etching using surface enhanced Raman spectroscopy (SERS). The electronic state of the carbon is sp2 on both the Si- and C-faces of 4H-SiC. The structures of the “carbon clusters” consist of two-dimensional graphitic flakes less than 2 nm and one-dimensional polyenes. The degree of graphitization on the C-face SiC is higher than those on the Si-face SiC. This study provides experimental evidence for “carbon clusters” existing on SiC surfaces following oxidation at atmospheric pressure and demonstrates that SERS is an effective technique to probe low concentration species on the SiC surface.
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81.65.Mq Oxidation
78.30.Hv Other nonmetallic inorganics
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states
81.05.Hd Other semiconductors
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