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27 Aug 2007

Volume 91, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 093110 (2007); http://dx.doi.org/10.1063/1.2775801 (3 pages)

M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, G. J. Salamo, D. Grigoriev, P. Schäfer, R. Köhler, and M. Hanke
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Subnanosecond ellipticity detector for laser radiation

S. D. Ganichev, J. Kiermaier, W. Weber, S. N. Danilov, D. Schuh, Ch. Gerl, W. Wegscheider, W. Prettl, D. Bougeard, and G. Abstreiter

Appl. Phys. Lett. 91, 091101 (2007); http://dx.doi.org/10.1063/1.2775809 (3 pages) | Cited 9 times

Online Publication Date: 27 August 2007

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A room temperature detector of terahertz laser radiation ellipticity has been developed based on the simultaneous measurements of three different photoelectric phenomena: circular photogalvanic effect, linear photogalvanic effect, and photon drag effect. Each of these effects, which have subnanosecond time constants, is monitored by different detector units stacked together in one detector.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Single quantum dot spectroscopy using a fiber taper waveguide near-field optic

Kartik Srinivasan, Oskar Painter, Andreas Stintz, and Sanjay Krishna

Appl. Phys. Lett. 91, 091102 (2007); http://dx.doi.org/10.1063/1.2775811 (3 pages) | Cited 10 times

Online Publication Date: 27 August 2007

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Photoluminescence spectroscopy of single InAs quantum dots at cryogenic temperatures ( ∼ 14 K) is performed using a micron-scale optical fiber taper waveguide as a near-field optic. A lower bound on the measured collection efficiency of quantum dot spontaneous emission into the fundamental guided mode of the fiber taper is estimated at 0.1%, and spatially resolved measurements with ∼ 600 nm resolution are obtained by varying the taper position with respect to the sample and using the fiber taper for both the pump and collection channels.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.79.Gn Optical waveguides and couplers

Time resolved microphotoluminescence studies of single InP nanowires grown by low pressure metal organic chemical vapor deposition

S. Reitzenstein, S. Münch, C. Hofmann, A. Forchel, S. Crankshaw, L. C. Chuang, M. Moewe, and C. Chang-Hasnain

Appl. Phys. Lett. 91, 091103 (2007); http://dx.doi.org/10.1063/1.2776358 (3 pages) | Cited 14 times

Online Publication Date: 27 August 2007

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The authors report optical studies of InP nanowires (NWs) grown by metal organic chemical vapor deposition. By means of low temperature microphotoluminescence experiments, the authors determined the optical properties of as-grown NWs. The emission of individual NWs is characterized by small linewidths as low as 2.3 meV. Blueshifts of the NW emission energy between 25 and 56 meV with respect to bulk InP are related to radial carrier confinement in nanowires with diameters between 15 and 50 nm. Time resolved investigations reveal a low surface recombination velocity of 6×102 cm/s and indicate thermally activated nonradiative surface recombination above approximately 20 K.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
78.60.-b Other luminescence and radiative recombination
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors

Luminescence properties of Tb3+–Sm3+ codoped glasses for white light emitting diodes

Xiaoluan Liang, Yunxia Yang, Chaofeng Zhu, Shuanglong Yuan, Guorong Chen, Allan Pring, and Fang Xia

Appl. Phys. Lett. 91, 091104 (2007); http://dx.doi.org/10.1063/1.2776857 (3 pages) | Cited 28 times

Online Publication Date: 27 August 2007

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Photoluminescence properties of silicate and borosilicate glasses codoped with Tb3+ and Sm3+ ions have been characterized by excitation and emission spectroscopies. When excited by ultraviolet light the glasses emit a combination of green and orange-red wavelengths giving white light. The ratio of the intensities of orange-red to green emissions can be tuned by varying both the concentration of the Sm3+ ion and an the composition of the glass matrix. The excitation and emission spectra show a self-quenching effect for the Sm3+ ions and an energy transfer from Tb3+ (5D4) to Sm3+ (4G5/2).
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78.55.Hx Other solid inorganic materials
85.60.Jb Light-emitting devices

Phase-matched second-harmonic generation in cross-linking polyurethane films by thermal-assisted optical poling

Jinhai Si and Kazuyuki Hirao

Appl. Phys. Lett. 91, 091105 (2007); http://dx.doi.org/10.1063/1.2776876 (3 pages) | Cited 3 times

Online Publication Date: 27 August 2007

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Phase-matched second-harmonic generation (SHG) in thermal-cross-linking polyurethane films was demonstrated using a thermal-assisted nonresonant optical poling technique. During the seeding process, samples heated in an oven were irradiated simultaneously by coherent superposition of the 1300 nm fundamental and 650 nm second-harmonic lights of a femtosecond laser. The photoinduced second-order optical nonlinearity of the polymer films seeded at elevated temperatures kept stable at room temperature. The measurements for the dependence of SHG on the film thickness showed that a χ(2) grating that satisfied the phase-matching condition for SHG was optically induced in the polymer films.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.-v Laser optical systems: design and operation

Fabrication of two-dimensional photonic crystal patterns on GaN-based light-emitting diodes using thermally curable monomer-based nanoimprint lithography

Kyeong-Jae Byeon, Seon-Yong Hwang, and Heon Lee

Appl. Phys. Lett. 91, 091106 (2007); http://dx.doi.org/10.1063/1.2776980 (3 pages) | Cited 26 times

Online Publication Date: 27 August 2007

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The fabrication process of photonic crystals in a p‐GaN layer was established to improve the light extraction efficiency of light-emitting diodes (LEDs) by using nanoimprint lithography and inductively coupled plasma (ICP) etching process. Due to low etch selectivity of imprinted pattern, Cr mask patterns were lifted-off from the p‐GaN surface and ICP etch process was followed using SiCl4-based plasma. As a result, two-dimensional pillar array patterns were uniformly fabricated on the p‐GaN layer and the photoluminescence intensity of the photonic crystal patterned LED was increased by 2.6 fold compared to that of the same LED sample without photonic crystal patterns.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
85.40.Hp Lithography, masks and pattern transfer

Observation of 394 nm electroluminescence from low-temperature sputtered n-ZnO/SiO2 thin films on top of the p-GaN heterostructure

Cheng Pin Chen, Min Yung Ke, Chien Cheng Liu, Yuan Jen Chang, Fu Hsiang Yang, and Jian Jang Huang

Appl. Phys. Lett. 91, 091107 (2007); http://dx.doi.org/10.1063/1.2777175 (3 pages) | Cited 17 times

Online Publication Date: 27 August 2007

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The authors report on the 394 nm UV light emission from low-temperature sputtered n-ZnO/SiO2 thin films on top of the p-GaN heterostructure. They compare samples with and without a SiO2 current blocking layer. With a SiO2 layer, electroluminescence spectrum shows a sharp emission peak at 394 nm, which is attributed to the recombination of accumulated carriers between n-ZnO/SiO2 and p-GaN/SiO2 junctions. As for the sample without a SiO2 layer, a broadband ranging from 400 to 800 nm is observed, which is due to Mg+ deep-level transition in the GaN along with defects in the ZnO layers.
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78.60.Fi Electroluminescence
68.35.Ct Interface structure and roughness

Efficient terahertz generation from two collinearly propagating CO2 laser pulses

Yi Jiang and Yujie J. Ding

Appl. Phys. Lett. 91, 091108 (2007); http://dx.doi.org/10.1063/1.2775095 (3 pages) | Cited 13 times

Online Publication Date: 27 August 2007

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Coherent terahertz pulses have been generated at 328.2 μm (914.1 GHz) by frequency-mixing two CO2 laser lines near 10 μm based on collinearly phase-matched difference-frequency generation in GaSe crystals. The highest average output power was measured to be 260 μW, corresponding to a peak output power of 510 mW. Both the average powers and normalized conversion efficiencies have been significantly improved over the previous results. The generated terahertz pulses are expected to have the narrowest linewidth dictated by the pulse width through Fourier transform based on the characteristics of the two CO2 laser beams.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Temperature-insensitive photonic crystal fiber interferometer for absolute strain sensing

Joel Villatoro, Vittoria Finazzi, Vladimir P. Minkovich, Valerio Pruneri, and Gonçal Badenes

Appl. Phys. Lett. 91, 091109 (2007); http://dx.doi.org/10.1063/1.2775326 (3 pages) | Cited 43 times

Online Publication Date: 27 August 2007

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The authors report a highly sensitive ( ∼ 2.8 pm/με) wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the propagating mode of the lead-in fiber which allows the coupling of only two modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient.
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42.81.Pa Sensors, gyros
07.60.Ly Interferometers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Pz Instruments for strain, force, and torque
42.70.Qs Photonic bandgap materials

Polarization engineering via staggered InGaN quantum wells for radiative efficiency enhancement of light emitting diodes

Ronald A. Arif, Yik-Khoon Ee, and Nelson Tansu

Appl. Phys. Lett. 91, 091110 (2007); http://dx.doi.org/10.1063/1.2775334 (3 pages) | Cited 63 times

Online Publication Date: 27 August 2007

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Staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition are demonstrated as improved active region for visible light emitters. Theoretical studies indicate that InGaN QW with step-function-like In content in the quantum well offers significantly improved radiative recombination rate and optical gain in comparison to the conventional type-I InGaN QW. Experimental results of light emitting diode (LED) structure utilizing staggered InGaN QW show good agreement with theory. Polarization band engineering via staggered InGaN quantum well allows enhancement of radiative recombination rate, leading to the improvement of photoluminescence intensity and LED output power.
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85.60.Jb Light-emitting devices
78.67.De Quantum wells

20 dB-enhanced coupling to slot photonic crystal waveguide using multimode interference coupler

Xiaonan Chen, Wei Jiang, Jiaqi Chen, Lanlan Gu, and Ray T. Chen

Appl. Phys. Lett. 91, 091111 (2007); http://dx.doi.org/10.1063/1.2768640 (3 pages) | Cited 11 times

Online Publication Date: 28 August 2007

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The authors experimentally demonstrate a slot photonic crystal structure for guiding light in a sub-100-nm-wide low-index region. A multimode interference-based coupling structure is introduced to couple light into such a narrow slot photonic crystal waveguide. A coupler of 1.26 μm long enhances the coupling efficiency by 20 dB for the quasi-transverse-electric mode over 35 nm optical bandwidth centered at 1562 nm. The measured transmission spectra are in good agreement with the simulated band diagram.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Passivation of type-II InAs/GaSb double heterostructure

Pierre-Yves Delaunay, Andrew Hood, Binh Minh Nguyen, Darin Hoffman, Yajun Wei, and Manijeh Razeghi

Appl. Phys. Lett. 91, 091112 (2007); http://dx.doi.org/10.1063/1.2776353 (3 pages) | Cited 21 times

Online Publication Date: 28 August 2007

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Focal plane array fabrication requires a well passivated material that is resistant to aggressive processes. The authors report on the ability of type-II InAs/GaSb superlattice heterodiodes to be more resilient than homojunctions diodes in improving sidewall resistivity through the use of various passivation techniques. The heterostructure consisting of two wide band gap (5 μm) superlattice contacts and a low band gap active region (11 μm) exhibits an R0A averaging of 13 Ω cm2. The devices passivated with SiO2, Na2S and SiO2 or polyimide did not degrade compared to the unpassivated sample and the resistivity of the sidewalls increased to 47 kΩ cm.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
81.65.Rv Passivation

Resonant optical in-well pumping of an (AlGaIn)(AsSb)-based vertical-external-cavity surface-emitting laser emitting at 2.35 μm

Nicola Schulz, Marcel Rattunde, Christian Ritzenthaler, Benno Rösener, Christian Manz, Klaus Köhler, Joachim Wagner, and Uwe Brauch

Appl. Phys. Lett. 91, 091113 (2007); http://dx.doi.org/10.1063/1.2773970 (3 pages) | Cited 12 times

Online Publication Date: 28 August 2007

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The semiconductor heterostructure design and lasing characteristics of an optically in-well pumped (AlGaIn)(AsSb)-based vertical-external-cavity surface-emitting laser (VECSEL) emitting at 2.35 μm are presented. The pump absorption in the active quantum wells at 1.96 μm has been enhanced by a higher-order microcavity resonance. VECSEL operation in-well pumped by a thulium-doped fiber laser has been demonstrated. Compared to a VECSEL barrier pumped at 1 μm, the in-well pumped device reaches a significantly higher power efficiency, and thus a higher output power at a given pump power, due to the smaller quantum deficit and hence reduced internal heat generation. Using an intracavity SiC heat spreader, a cw output power in excess of 3 W has been achieved at a heat sink temperature of −15 °C, and still more than 2 W at +15 °C.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

White light generation by frequency upconversion in Tm3+/Ho3+/Yb3+-codoped fluorolead germanate glass

A. S. Gouveia-Neto, L. A. Bueno, R. F. do Nascimento, E. A. da Silva, Jr., E. B. da Costa, and V. B. do Nascimento

Appl. Phys. Lett. 91, 091114 (2007); http://dx.doi.org/10.1063/1.2775043 (3 pages) | Cited 56 times

Online Publication Date: 28 August 2007

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White light was produced exploiting an additive synthesis of red, green, and blue fluorescence through frequency upconversion in fluorolead-germanate glass codoped with Ho3+, Tm3+, and Yb3+. The 475, 540, and 650 nm signals were, respectively, assigned to thulium (1G4-3H6) and holmium (5S2;5F4)→5I8 and 5F5→5I8, excited via energy tranfer from ytterbium. The dopant concentrations were adjusted, yielding the emission of a wide color gamut in the visible spectrum and the production of white light using excitation at 975 nm. The spectral positions and purity (blue, 97%; green, 100%; red, 95%) of the three colors produced CIE-X = 0.3438 and CIE-Y = 0.3639 coordinates.
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78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Random lasing emission from a red fluorescent dye doped polystyrene film containing dispersed polystyrene nanoparticles

Dingke Zhang, Yanping Wang, and Dongge Ma

Appl. Phys. Lett. 91, 091115 (2007); http://dx.doi.org/10.1063/1.2778550 (3 pages) | Cited 7 times

Online Publication Date: 30 August 2007

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The authors report a random lasing emission from 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran doped polystyrene thin films by introducing polystyrene nanoparticles. The aspects of concentration and diameter of polystyrene nanoparticles have been intensively investigated and found that the lasing occurs due to the scattering role of polystyrene nanoparticles. The devices emit a resonance multimode peak centered at a wavelength of 630 nm with a mode linewidth of less than 0.35 nm and exhibit threshold excitation intensity of as low as 0.06 mJ pulse−1 cm−2. The microscopic laser cavities formed by multiple scattering have been captured. The demonstration of random laser opens up the possibility of using organic scattering as alternative sources of coherent light emission.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.70.Jk Polymers and organics
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers

Structural and lasing characteristics of ultrathin hexagonal ZnO nanodisks grown vertically on silicon-on-insulator substrates

Dingshan Yu, Yujie Chen, Baojun Li, Xudong Chen, Mingqiu Zhang, Fuli Zhao, and Shan Ren

Appl. Phys. Lett. 91, 091116 (2007); http://dx.doi.org/10.1063/1.2779094 (3 pages) | Cited 21 times

Online Publication Date: 30 August 2007

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Hexagonal ZnO nanodisks were grown on silicon-on-insulator substrates by vapor-transport method without catalysts. The resulting nanodisks possess ultrathin thickness (10–20 nm) and most of them present vertical orientation on the substrate surface. Under optical excitation, these ultrathin nanodisks exhibit ultraviolet lasing emission with the excitation threshold of 205 μJ/cm2 and emission lifetime of 2 ps at room temperature. The detailed lasing analysis indicates that whispering-gallery-mode lasing may occur in the ZnO nanodisks.
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81.07.Bc Nanocrystalline materials
81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
61.46.Hk Nanocrystals
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors

Experimental demonstration of a wavelength demultiplexer based on negative-refractive photonic-crystal components

Takashi Matsumoto, Tomohiko Asatsuma, and Toshihiko Baba

Appl. Phys. Lett. 91, 091117 (2007); http://dx.doi.org/10.1063/1.2779927 (3 pages) | Cited 12 times

Online Publication Date: 30 August 2007

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Negative refraction of light was observed at near-infrared wavelengths in a silicon-on-insulator photonic-crystal-slab superprism having low-loss interface structures. It was used for wavelength demultiplexing as a diffraction grating, in combination with a photonic-crystal superlens used for focusing light beams. Coarse wavelength demultiplexing action with a channel spacing of 7–27 nm was demonstrated in a device whose size was only 80×100 μm2 (excluding input and output waveguides). These results agree well with those obtained by a finite-difference time-domain simulation.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Dj Gratings
42.70.Qs Photonic bandgap materials
42.82.Gw Other integrated-optical elements and systems

Enhanced In(Ga)As/GaAs quantum dot based electro-optic modulation at 1.55 μm

G. Moreau, A. Martinez, D.-Y. Cong, K. Merghem, A. Miard, A. Lemaître, P. Voisin, A. Ramdane, I. Krestnikov, A. R. Kovsh, M. Fischer, and J. Koeth

Appl. Phys. Lett. 91, 091118 (2007); http://dx.doi.org/10.1063/1.2778759 (3 pages) | Cited 4 times

Online Publication Date: 31 August 2007

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The authors report a study of the linear electro-optic coefficient in waveguides containing InGaAs/GaAs quantum dots with a band gap at 1.3 μm. The Pockels effect is investigated in the 1.55 μm telecommunication window. The measured linear electro-optic coefficient for InGaAs/GaAs is ∼ 3.4×10−11 m/V, much higher than that of the bulk or quantum well material. An ∼ 35% enhancement of the phase variation is achieved compared to that obtained in bulk GaAs waveguides. Finally, a spectral bandwidth of ∼ 100 nm is demonstrated in the 1.5–1.6 μm window.
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78.67.Hc Quantum dots
78.20.Jq Electro-optical effects
42.79.Gn Optical waveguides and couplers

Optical manipulation and rotation of liquid crystal drops using high-index fiber-optic tweezers

Kazi Sarwar Abedin, Charles Kerbage, Alberto Fernandez-Nieves, and David A. Weitz

Appl. Phys. Lett. 91, 091119 (2007); http://dx.doi.org/10.1063/1.2775321 (3 pages) | Cited 3 times

Online Publication Date: 31 August 2007

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We report an optical fiber tweezer based on high-index material for trapping and optical manipulation of microscale particles in water. The use of a high-index material increases the trapping force with respect to the more common silica, through tighter focusing of light. We demonstrate the potential of this simple and versatile device by trapping and rotating nematic liquid crystal drops. We monitor the rotation of the drop by detecting light modulation observed with the same fiber using backscattered light, which exhibits modulation in intensity due to the rotation of the drop; this further extends the capabilities of the fiber tweezers.
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87.80.Cc Optical trapping
42.81.-i Fiber optics
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
82.70.Dd Colloids
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Some comments on contact charge relaxation

Peter M. Ireland

Appl. Phys. Lett. 91, 091501 (2007); http://dx.doi.org/10.1063/1.2776021 (3 pages)

Online Publication Date: 27 August 2007

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The established contact charge relaxation scheme of Matsuyama and Yamamoto [J. Phys. D 28, 2418 (1995); 30, 2170 (1997) ] is reassessed in light of the observations of Horn and Smith [Science 256, 362 (1992) ] and Horn et al. [Nature (London) 366, 442 (1993) ] of charge relaxation between separated charged surfaces. The multiple partial discharges observed in these studies are inconsistent with a scheme where onset and extinction are both described by a single Paschen curve. A modified version of the established scheme is therefore proposed.
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52.80.-s Electric discharges
77.22.Jp Dielectric breakdown and space-charge effects

Puzzling differences in bismuth and lead plasmas: Evidence for the significant role of neutrals in cathodic vacuum arcs

André Anders and Georgy Yu. Yushkov

Appl. Phys. Lett. 91, 091502 (2007); http://dx.doi.org/10.1063/1.2776858 (3 pages) | Cited 6 times

Online Publication Date: 27 August 2007

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Time-dependent ion charge state measurements for Pb and Bi cathodic arc plasmas revealed unexpected differences: the mean Bi ion charge state dropped much stronger and with a longer time constant. It is shown that the differences in thermal conductivity and vapor pressure led to much higher neutral density for Bi, which in turn can cause charge exchange collisions. The results have implications beyond Pb and Bi plasmas: most importantly, they imply that the “true” ion charge states, as emitted from the cathode spots, are higher than what is generally measured and published.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.50.Dg Plasma sources
52.70.Nc Particle measurements
52.25.Fi Transport properties
52.25.Ya Neutrals in plasmas

Improvement of output characteristics of a relativistic magnetron by creating asymmetric radio-frequency magnetic fields

Hae Jin Kim and Jin Joo Choi

Appl. Phys. Lett. 91, 091503 (2007); http://dx.doi.org/10.1063/1.2775327 (3 pages) | Cited 1 time

Online Publication Date: 27 August 2007

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Asymmetric magnetic field geometry is explored by inserting three metal tuners asymmetrically into the resonators of the A6 magnetron. The authors investigate the operating characteristics of a relativistic magnetron with asymmetrically perturbed radio-frequency (rf) magnetic fields caused by metal tuners using a three dimensional, electromagnetic particle-in-cell code MAGIC3D. By configuring perturbed rf magnetic fields, the operating characteristics of a relativistic magnetron are superior compared to those using uniform rf magnetic fields. Most significantly, by creating asymmetrically perturbed rf magnetic fields, the output power of the A6 magnetron increased by about 40% compared to the case of uniform rf magnetic fields.
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41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Study of selective amorphous silicon etching to silicon nitride using a pin-to-plate dielectric barrier discharge in atmospheric pressure

Se-Jin Kyung, Jae-Beom Park, June-Hee Lee, Jong-Tae Lim, and Geun-Young Yeom

Appl. Phys. Lett. 91, 091504 (2007); http://dx.doi.org/10.1063/1.2779096 (3 pages) | Cited 2 times

Online Publication Date: 30 August 2007

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Remote-type atmospheric pressure plasmas were generated using a modified dielectric barrier discharge with the powered electrode consisting of multipins instead of a conventional blank planar plate. For the N2/NF3 gas mixture, a high etch rate of a:Si close to 115 nm/s was obtained by adding 300 SCCM (SCCM denotes cubic centimeter per minute at STP) of NF3 to N2 [50 SLM (standard liters per minute)] at an ac rms voltage of 8.5 kV (2.5 kW, 30 kHz). However, the selectivity of a:Si to Si3N4 was as low as 1.3. A selectivity of a:Si/Si3N4>5.0 could be obtained while maintaining an etch rate of a:Si at 110 nm/s by adding 250 SCCM CF4 to the N2 (50 SLM)/NF3 (300 SCCM) mixture through the formation of a C–F polymer layer preferentially on the Si3N4 surface.
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81.05.Hd Other semiconductors
81.65.Cf Surface cleaning, etching, patterning
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Effects of alloying and localized electronic states on the resonant Raman spectra of Zn1−xMgxO nanocrystals

J. D. Ye, K. W. Teoh, X. W. Sun, G. Q. Lo, D. L. Kwong, H. Zhao, S. L. Gu, R. Zhang, Y. D. Zheng, S. A. Oh, X. H. Zhang, and S. Tripathy

Appl. Phys. Lett. 91, 091901 (2007); http://dx.doi.org/10.1063/1.2775813 (3 pages) | Cited 16 times

Online Publication Date: 27 August 2007

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Using resonant Raman spectroscopy, the authors report on the alloying effect and localization of electronic states in Zn1−xMgxO (x<0.15) nanostructures with average sizes in the range of 20–150 nm. Anomalous intensity enhancement of the second-order longitudinal optical phonon has been observed, which is due to Fröhlich interaction via the localized exciton as the resonant intermediate electronic states. The alloying-induced disorder due to Mg incorporation led to the enhancement of exciton localization as well as the asymmetric broadening of longitudinal optical phonon line shape. The composition in ZnMgO could be determined by the first-order longitudinal optical phonon frequency via a bowinglike quadratic fit. This simple relationship is in perfect match to the modified random-element-isodisplacement model and provides a nondestructive approach to probe the quantitative composition distributions in wurtzite ZnMgO alloy system.
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78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
61.46.-w Structure of nanoscale materials
63.20.kk Phonon interactions with other quasiparticles
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
71.55.Gs II-VI semiconductors

Stability and electronic structures of CuxTe

Juarez L. F. Da Silva, Su-Huai Wei, Jie Zhou, and Xuanzhi Wu

Appl. Phys. Lett. 91, 091902 (2007); http://dx.doi.org/10.1063/1.2775835 (3 pages) | Cited 11 times

Online Publication Date: 27 August 2007

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In this work, the authors study the stability and electronic properties of CuxTe as a function of the Cu/Te ratio using first-principles calculations. They find that CuxTe shows bistability with energy minimum at x ≈ 1.25 and x ≈ 1.75. At low x, CuxTe is more stable in the tetragonal-based structures, whereas for x>1.47, it is more stable in the trigonal-based structures. The valence-band maximum of Cu2Te is found to be 0.7 eV higher than that of CdTe, indicating that it can easily be doped p type. The Cu diffusion barriers and hole density decrease with increasing Cu concentration, indicating that for x ∼ 2, ionic conductivity may play a role.
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71.20.Nr Semiconductor compounds
71.10.-w Theories and models of many-electron systems
71.15.-m Methods of electronic structure calculations
66.30.H- Self-diffusion and ionic conduction in nonmetals
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