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3 Jul 2006

Volume 89, Issue 1, Articles (01xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 011901 (2006); http://dx.doi.org/10.1063/1.2218670 (3 pages)

L. S. Wang, S. Tripathy, B. Z. Wang, J. H. Teng, S. Y. Chow, and S. J. Chua
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70-mm-long periodically poled Mg-doped stoichiometric LiNbO3 devices for nanosecond optical parametric generation

Masayuki Maruyama, Hirochika Nakajima, Sunao Kurimura, Nan Ei Yu, and Kenji Kitamura

Appl. Phys. Lett. 89, 011101 (2006); http://dx.doi.org/10.1063/1.2219084 (3 pages) | Cited 10 times

Online Publication Date: 5 July 2006

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A low-threshold, nanosecond, optical parametric generator (OPG) was produced by using a 70-mm-long, periodically poled, Mg-doped, stoichiometric LiNbO3 (PPMgSLN). The periodically poled structure was obtained by applying an electric field of 1.8 kV/mm, which is lower than the coercive field of 3.9 kV/mm. The PPMgSLN OPG pumped with a 6 ns, 6.8 kHz, Nd:YAG microchip laser had a generation threshold of 12 MW/cm2 and a slope efficiency of 37% of signal at 1.61 μm.
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42.70.Mp Nonlinear optical crystals
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Yj Optical parametric oscillators and amplifiers
61.66.Bi Elemental solids
61.66.Dk Alloys
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.Jq Electro-optical effects

Long-wavelength vertical-cavity surface-emitting laser using an electro-optic index modulator with 10 nm tuning range

C. Levallois, B. Caillaud, J.-L. de Bougrenet de la Tocnaye, L. Dupont, A. Le Corre, H. Folliot, O. Dehaese, and S. Loualiche

Appl. Phys. Lett. 89, 011102 (2006); http://dx.doi.org/10.1063/1.2219144 (3 pages) | Cited 1 time

Online Publication Date: 5 July 2006

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We demonstrate an original approach to achieving a tunable 1.55 μm vertical-cavity surface-emitting laser. The tunability is based on an electro-optic index modulator using nanosized droplets of liquid crystal as a phase layer. Such an approach can produce a robust and a low-cost device. A 10 nm tuning range with less than 170 V applied voltage has been demonstrated. The device is formed by a conventional InP-based active region with an epitaxial and a dielectric Bragg mirror. This optically pumped device exhibits an excellent side-mode suppression ratio of higher than 20 dB over the whole spectral range.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Hp Optical processors, correlators, and modulators
42.79.Kr Display devices, liquid-crystal devices
42.79.Bh Lenses, prisms and mirrors
42.70.Df Liquid crystals

High-temperature random lasing in ZnO nanoneedles

H. Y. Yang, S. P. Lau, S. F. Yu, A. P. Abiyasa, M. Tanemura, T. Okita, and H. Hatano

Appl. Phys. Lett. 89, 011103 (2006); http://dx.doi.org/10.1063/1.2219419 (3 pages) | Cited 11 times

Online Publication Date: 5 July 2006

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We report the high-temperature ultraviolet random laser action in ZnO nanoneedles. The characteristic temperature of the ZnO nanoneedle lasers was derived to be 138 K in the temperature range from 300 to 615 K. The cavity length of the random lasers as a function of temperature was determined by Fourier transform spectroscopy. The cavity length decreased with an increase in temperature from ∼ 14 μm at 300 K to  ∼ 2 μm at 550 K. The optical gain of the ZnO nanoneedle lasers at high temperature is attributed to a self-compensation mechanism in the cavity length.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Two-photon photoluminescence and excitation spectra of InGaN/GaN quantum wells

Q. Li, S. J. Xu, G. Q. Li, D. C. Dai, and C. M. Che

Appl. Phys. Lett. 89, 011104 (2006); http://dx.doi.org/10.1063/1.2218772 (3 pages) | Cited 6 times

Online Publication Date: 6 July 2006

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We report an observation of efficient two-photon photoluminescence (TPL) of InGaN/GaN multi-quantum-well (MQW) structures using broadband femtosecond near-infrared excitation laser. Near quadratic excitation-intensity dependence and asymmetric collinear interferometric autocorrelation trace of the TPL signal unambiguously verify the nonlinearity of the TPL process. We also measured the excitation spectrum of the TPL signal and found that it can be fitted well with the theoretical two-photon absorption coefficient formula for direct wide gap semiconductors. The decay time of the TPL signal was determined using a time-resolved photoluminescence technique. These results demonstrate the strong nonlinear optical property of InGaN/GaN MQWs.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics

Charge photogeneration effect on the exciplex emission from thin organic films

J. Kalinowski, M. Cocchi, D. Virgili, and C. Sabatini

Appl. Phys. Lett. 89, 011105 (2006); http://dx.doi.org/10.1063/1.2218821 (3 pages) | Cited 8 times

Online Publication Date: 6 July 2006

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The photoexcited singlet and triplet exciplex emission of thin photocondcuctive films containing an amine derivative N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′diamine (TPD) electron donor and the bathophenathroline (BPT) electron acceptor drops largely with electric fields, falling down to about 20% of its zero-field value at high fields. This strong electric-field-induced exciplex emission quenching is interpreted in terms of the charge-imposed decay of singlet molecular excitons of TPD acting as precursors of the exciplexes and charge photogenerated on the TPD:BPT contacting sites. The favorable interrelation between the ionization potential of the donor and electron affinity of the acceptor leads there to an efficient field-enhanced exciton dissociation. The electrons trapped on acceptor molecules act in turn as charged exciton quenching centers.
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78.66.Qn Polymers; organic compounds
72.40.+w Photoconduction and photovoltaic effects
71.35.-y Excitons and related phenomena

First direct observation of self-imaging effect in active multimode-interference semiconductor laser diodes

Syogo Shimizu, Mohd Dannial Bin Razali, Kenichi Kasahara, Kiichi Hamamoto, Masaki Ohya, Koichi Naniwae, Jan De Merlier, Kazuhiro Shiba, Shinya Sudo, and Tatsuya Sasaki

Appl. Phys. Lett. 89, 011106 (2006); http://dx.doi.org/10.1063/1.2219087 (3 pages)

Online Publication Date: 6 July 2006

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We report the first direct observation of the self-imaging effect in active multimode-interference semiconductor laser diodes (MMI-SLDs). Interference patterns inside laser diode waveguides were obtained by using the electroluminescence (EL) method. To the best of our knowledge, this result is the first direct observation of the self-imaging effect in self-photon-emitting active waveguides such as laser diodes. The observed EL pattern confirms the adequateness of the design of the higher light output-aimed MMI-SLDs.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Optical gain in dye-impregnated oxidized porous silicon waveguides

C. J. Oton, D. Navarro-Urrios, N. E. Capuj, M. Ghulinyan, L. Pavesi, S. González-Pérez, F. Lahoz, and I. R. Martín

Appl. Phys. Lett. 89, 011107 (2006); http://dx.doi.org/10.1063/1.2219121 (3 pages) | Cited 8 times

Online Publication Date: 6 July 2006

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Positive optical gain under pulsed excitation in oxidized porous silicon planar waveguides impregnated with Nile blue (LC 6900) is reported. Amplified spontaneous emission measurements show a dramatic line narrowing when the pump energy is increased, together with a strong superlinear behavior. Variable stripe length measurements were performed to characterize quantitatively the amplification, and an unambiguous transition from losses to gain is observed with a threshold of ∼ 3 mJ/cm2 at 700 nm. A maximum gain coefficient of 8.7 cm−1 ( ∼ 40 dB/cm) is reported. Shifting excitation spot measurements confirm the reliability of our results. This system is interesting in view of an optically pumped silicon-based pulsed laser.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.55.Mv Dye lasers
42.70.Hj Laser materials

Hole emitter of photonic quantum ring

O’Dae Kwon, M. J. Kim, S.-J. An, D. K. Kim, S. E. Lee, J. Bae, J. H. Yoon, B. H. Park, J. Y. Kim, and J. Ahn

Appl. Phys. Lett. 89, 011108 (2006); http://dx.doi.org/10.1063/1.2219346 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2006

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We report on the observation of “hole” whispering gallery lasers from semiconductor microcavities with three dimensional optical confinement, with thresholds potentially reducible to micro- to nanoampere regimes according to a quadratic size-dependent reduction, consistent with a photonic quantum corral effect of naturally formed recombinant quantum rings. If the device size grows over a critical diameter, the quantum ring whispering gallery then begins to disappear. However, cooperative small hole laser arrays, exhibiting photonic crystal structure properties, avoid the criticality and open a possibility of constructing practical high-density electropumped emitter arrays.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials

Design of a ZnMnSe/ZnMgSe spin-polarized terahertz quantum cascade laser tunable by magnetic field

Ivana Savić, Zoran Ikonić, Nenad Vukmirović, Dragan Indjin, Paul Harrison, and Vitomir Milanović

Appl. Phys. Lett. 89, 011109 (2006); http://dx.doi.org/10.1063/1.2219423 (3 pages) | Cited 2 times

Online Publication Date: 6 July 2006

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A design of a magnetic field tunable ZnMnSe/ZnMgSe terahertz quantum cascade laser is proposed. It relies on the spin-dependent potential induced by a magnetic field. The electron dynamics are calculated using the Boltzmann equation approach, with electron-longitudinal optical phonon, electron-longitudinal acoustic phonon, and electron-electron scattering included. Tunability of the emission energy between 10 and 26 meV, and 38 and 42 meV, for transitions of spin-down and spin-up electrons, respectively, may be achieved by varying a magnetic field up to 5 T, at a temperature of 1.5 K. Population inversion of up to 42% for spin-down and 27% for spin-up electrons is predicted, which in conjunction with the estimated waveguide losses, yields sufficient gain for laser operation.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
78.20.Ls Magneto-optical effects
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
72.25.Dc Spin polarized transport in semiconductors

Thermal relaxation time and heat distribution in pulsed InGaAs quantum dot lasers

P. K. L. Chan, K. P. Pipe, Z. Mi, J. Yang, P. Bhattacharya, and D. Lüerßen

Appl. Phys. Lett. 89, 011110 (2006); http://dx.doi.org/10.1063/1.2219721 (3 pages) | Cited 7 times

Online Publication Date: 7 July 2006

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Using a charge coupled device-based thermoreflectance technique, we achieve a high-resolution ( ∼ 700 nm) cross-sectional temperature profile of a semiconductor laser. This two-dimensional profile allows us to identify separate heat sources due to contact heating and nonradiative recombination in the active region. By adapting the technique to pulsed operation and varying the laser’s duty cycle, we measure the thermal relaxation time constant. We also quantitatively determine the heat transfer from device-internal heat sources and demonstrate both the large effect of lateral heat spreading and the distinction between a laser’s top surface temperature and its active region temperature.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Gain narrowing and random lasing from dye-doped polymer-dispersed liquid crystals with nanoscale liquid crystal droplets

Y. J. Liu, X. W. Sun, H. I. Elim, and W. Ji

Appl. Phys. Lett. 89, 011111 (2006); http://dx.doi.org/10.1063/1.2219988 (3 pages) | Cited 18 times

Online Publication Date: 7 July 2006

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Dye-doped polymer-dispersed liquid crystals have been studied for random lasing. The dye-doped polymer-dispersed liquid crystal film was fabricated by photoinitiated polymerization with a collimated 514.5 nm Ar+ laser beam. Scanning electron microscopy analysis showed that most liquid crystal droplets in polymer matrix ranged from 20 to 80 nm. Gain narrowing and random lasing from dye-doped polymer dispersed liquid crystals were observed under the excitation of a frequency-doubled Nd:YAG (yttrium aluminum garnet) laser operating at a wavelength of 532 nm. The possible mechanism was proposed to explain the random lasing. The threshold of the random lasing was about 25 μJ/pulse. The linewidth of the lasing peaks was about 1 nm. With the film thickness of 6.5 μm, the lasing mode was nearly transverse electric polarized.
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42.55.Zz Random lasers
42.70.Df Liquid crystals
42.70.Hj Laser materials

GaN ultraviolet avalanche photodiodes with optical gain greater than 1000 grown on GaN substrates by metal-organic chemical vapor deposition

J. B. Limb, D. Yoo, J. H. Ryou, W. Lee, S. C. Shen, R. D. Dupuis, M. L. Reed, C. J. Collins, M. Wraback, D. Hanser, E. Preble, N. M. Williams, and K. Evans

Appl. Phys. Lett. 89, 011112 (2006); http://dx.doi.org/10.1063/1.2219390 (3 pages) | Cited 40 times

Online Publication Date: 7 July 2006

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We report the performance of GaN p-i-n ultraviolet avalanche photodiodes grown on bulk GaN substrates by metal-organic chemical vapor deposition. The low dislocation density in the devices enables low reverse-bias dark currents prior to avalanche breakdown for ∼ 30 μm diameter mesa photodetectors. The photoresponse is relatively independent of the bias voltage prior to the onset of avalanche gain which occurs at an electric field of ∼ 2.8 MV/cm. The magnitude of the reverse-bias breakdown voltage shows a positive temperature coefficient of ∼ 0.05 V/K, confirming that the avalanche breakdown mechanism dominates. With ultraviolet illumination at λ ∼ 360 nm, devices with mesa diameters of ∼ 50 μm achieve stable maximum optical gains greater than 1000. To the best of our knowledge, this is the highest optical gain achieved for GaN-based avalanche photodiodes and the largest area III-N avalance photodetectors yet reported.
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85.60.Dw Photodiodes; phototransistors; photoresistors
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Phase effect on flow control for dielectric barrier plasma actuators

K. P. Singh and Subrata Roy

Appl. Phys. Lett. 89, 011501 (2006); http://dx.doi.org/10.1063/1.2218770 (3 pages) | Cited 3 times

Online Publication Date: 6 July 2006

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Active control of flow has a wide range of applications. Specifically, mitigation of detachment due to the weakly ionized gas flow past a flat plate at an angle of attack is studied using two asymmetric sets of electrode pairs kept at a phase lag. The equations governing the dynamics of electrons, helium ions, and neutrals are solved self-consistently with charge-Poisson equation. The eletrodynamic forces produced by two actuators largely depend on the relative phase between the potentials applied to rf electrodes and distance between them. A suitable phase and an optimum distance exist between two actuators for effective separation control.
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52.75.-d Plasma devices
52.30.-q Plasma dynamics and flow
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.25.Ya Neutrals in plasmas
02.60.Lj Ordinary and partial differential equations; boundary value problems

Electron and metastable state interactions in two-step ionization waves

Nicholas S. Siefert, Brian L. Sands, and Biswa N. Ganguly

Appl. Phys. Lett. 89, 011502 (2006); http://dx.doi.org/10.1063/1.2219982 (3 pages) | Cited 5 times

Online Publication Date: 7 July 2006

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We demonstrate the use of a microwave hairpin resonator to measure the time-dependent, phase-resolved electron number density in ionization waves. Under our argon glow discharge conditions, the instability was caused by two-step ionization; and the wave frequency depended on the volume quenching rate of the metastable states. We measured the 1s5 metastable state density using diode laser absorption. The peak electron number density lagged behind the peak metastable state density by 60°. This phase shift reveals the nonlocal nature of the electron kinetics due to two-step ionization.
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52.25.Jm Ionization of plasmas
52.70.Gw Radio-frequency and microwave measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Hc Glow; corona
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.25.Fi Transport properties
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Nanoscale epitaxial overgrowth process and properties of GaN layers on Si (111) substrates

L. S. Wang, S. Tripathy, B. Z. Wang, J. H. Teng, S. Y. Chow, and S. J. Chua

Appl. Phys. Lett. 89, 011901 (2006); http://dx.doi.org/10.1063/1.2218670 (3 pages) | Cited 14 times

Online Publication Date: 5 July 2006

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Nanoscale epitaxial overgrowth has been explored to realize continuous specular GaN films on patterned SiO2/GaN/Si (111) substrates. We have employed both polystyrene-based nanosphere and interferometric lithographies to form the nanohole array patterns and then subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition. The nanoscale epitaxial overgrowth process of GaN layers is studied by scanning and transmission electron microscopy measurements. Optical spectroscopic methods such as microphotoluminescence and micro-Raman scattering show an improvement of the optical and crystalline quality in such overgrown GaN layers when compared to GaN simultaneously grown on bulk Si (111) without patterning. Realization of such thicker and good quality GaN layer would be useful to achieve III-nitride-based optoelectronic integration on Si substrates.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Nd Micro- and nanolithography
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Structure and photoluminescence properties of evaporated GeOx thin films

M. Ardyanian, H. Rinnert, X. Devaux, and M. Vergnat

Appl. Phys. Lett. 89, 011902 (2006); http://dx.doi.org/10.1063/1.2218830 (3 pages) | Cited 16 times

Online Publication Date: 5 July 2006

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Amorphous GeOx alloys were prepared by evaporation of GeO2 powder on substrates maintained at 100 °C. The evolution of the structure was investigated by infrared-absorption spectrometry, Raman spectrometry and transmission electron microscopy experiments for annealing temperatures less than 600 °C. These experiments allowed us to follow the phase separation of the alloy and to observe the appearance of amorphous and crystallized Ge aggregates. The evolution of the photoluminescence in the range of 560–1550 nm was correlated to the structure of the films.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
68.55.-a Thin film structure and morphology
78.66.Db Elemental semiconductors and insulators
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth

Enhanced optical second harmonic generation in hybrid polymer nanoassemblies based on coupled surface plasmon resonance of a gold nanoparticle array

Miki Ishifuji, Masaya Mitsuishi, and Tokuji Miyashita

Appl. Phys. Lett. 89, 011903 (2006); http://dx.doi.org/10.1063/1.2219086 (3 pages) | Cited 11 times

Online Publication Date: 5 July 2006

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Effective utilization of coupled surface plasmon resonance from gold nanoparticles was demonstrated experimentally for optoelectronic applications based on second-order nonlinear optics. Hybrid polymer nanoassemblies were constructed by manipulating gold nanoparticle arrays with nonlinear optical active polymer nanosheets to investigate the second harmonic generation. The gold nanoparticle arrays were assembled on heterodeposited polymer nanosheets. The second harmonic light intensity was enhanced by a factor of 8. The observed enhancement was attributed to coupling of surface plasmons between two adjacent gold nanoparticles, thereby enhancing the surface electromagnetic field around the nanoparticles at the fundamental light wavelength (1064 nm).
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.68.+m Optical properties of surfaces
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Phase selective growth and properties of rhombohedral and cubic indium oxide

Ch. Y. Wang, V. Cimalla, H. Romanus, Th. Kups, G. Ecke, Th. Stauden, M. Ali, V. Lebedev, J. Pezoldt, and O. Ambacher

Appl. Phys. Lett. 89, 011904 (2006); http://dx.doi.org/10.1063/1.2219125 (3 pages) | Cited 28 times

Online Publication Date: 5 July 2006

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Phase selective growth of rhombohedral and cubic indium oxide polytypes was studied. The selective growth of different polytypes was achieved by adjusting substrate temperature and trimethylindium flow rate during metal organic chemical vapor deposition on c-plane sapphire. The optical band gaps of the cubic and rhombohedral phases were determined to be ∼ 3.7 and ∼ 3.0 eV, respectively. On the basis of the performed structural investigations, a phenomenological model of the nucleation and growth of highly textured cubic In2O3 on Al2O3 (0001) is proposed.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Propagation of surface water wave pulses over an uneven topographical bottom

Liang-Shan Chen, Sheng Li, Thomas F. George, Chao-Hsien Kuo, and Xin Sun

Appl. Phys. Lett. 89, 011905 (2006); http://dx.doi.org/10.1063/1.2219130 (3 pages) | Cited 1 time

Online Publication Date: 5 July 2006

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The propagation of surface water wave pulses over a topographical bottom with randomly arranged cylindrical steps is investigated by multiple scattering theory. It is shown that the waves within a certain frequency range can be localized due to the strong multiple scattering process. In the localized state, the wave intensity decreases exponentially as the transmitted distance increases. By making use of this effect, some components contained in the pulse can be filtered or inhibited by the cylinder ensemble and trapped for a relatively long period of time until dissipation.
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47.35.-i Hydrodynamic waves

Carrier capture times of the localized states in an InGaN thin film with indium-rich nanocluster structures

Hsiang-Chen Wang, Yen-Cheng Lu, Cheng-Yen Chen, and C. C. Yang

Appl. Phys. Lett. 89, 011906 (2006); http://dx.doi.org/10.1063/1.2219131 (3 pages) | Cited 5 times

Online Publication Date: 5 July 2006

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A femtosecond nondegenerate pump-probe technique of using two beta barium borate crystals for frequency doubling a 7 fs Ti:sapphire laser is used for studying the ultrafast carrier dynamics in an InGaN thin film, in which nanoscale indium-rich clusters have been observed. The carrier capture time of the localized states (the cluster states) from the free-carrier states (the states of the background compound) is calibrated. The initial rise times of the differential transmission of the probe intensity are calibrated to give the time constant of about 300 fs for the degenerate cases over the whole photoluminescence spectral range and for the nondegenerate cases, in which both pump and probe wavelengths correspond to the free-carrier states. However, when the carriers are excited in the free-carrier states and probed in the localized states, the rise time increases to the range of 590–715 fs, which represents the carrier capture time of the localized states from the free-carrier states.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
78.47.-p Spectroscopy of solid state dynamics

Impurity-induced phase stabilization of semiconductors

Gustavo M. Dalpian, Yanfa Yan, and Su-Huai Wei

Appl. Phys. Lett. 89, 011907 (2006); http://dx.doi.org/10.1063/1.2218311 (3 pages) | Cited 6 times

Online Publication Date: 5 July 2006

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We propose an approach to stabilize the cubic zinc-blende (ZB) phase of semiconductor compounds that are usually more stable in the hexagonal wurtzite (WZ) phase. This approach is based on impurity doping and we take advantage of the band offset between the ZB and WZ phases. We show that introduction of donors should stabilize the one with lower conduction band (ZB), whereas holes should stabilize the one with higher valence band (WZ). A mechanism to invert the valence band offset is proposed in order to stabilize the ZB phase through holes. We used GaN, ZnO, and AlN as examples.
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71.20.Nr Semiconductor compounds
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
71.55.Eq III-V semiconductors
71.55.Gs II-VI semiconductors

Two-dimensional nonclose-packed colloidal crystals formed by spincoating

Peng Jiang, Tushar Prasad, Michael J. McFarland, and Vicki L. Colvin

Appl. Phys. Lett. 89, 011908 (2006); http://dx.doi.org/10.1063/1.2218832 (3 pages) | Cited 45 times

Online Publication Date: 6 July 2006

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We report a simple spin-coating technique for the production of monolayer nonclose-packed colloidal crystals. Dispersions of submicron silica spheres in triacrylate monomers are spincoated and polymerized to form two-dimensional colloidal crystal-polymer nanocomposites. By removing the polymer matrix, wafer-scale nonclose-packed colloidal crystals with high crystalline quality can be made. The technique is compatible with standard microfabrication and allows for the production of microstructures for potential devices. Normal-incidence reflectivity spectra in the visible and near-infrared regions show sharp peaks due to Bragg diffraction from the colloidal monolayers. The peak position matches with the theoretical prediction using scalar wave approximation.
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81.16.-c Methods of micro- and nanofabrication and processing
82.35.-x Polymers: properties; reactions; polymerization
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
82.70.Dd Colloids
78.20.-e Optical properties of bulk materials and thin films

Unusual hydrogen distribution and its change in hydrogenated amorphous silicon prepared using bias electric-field molecular beam deposition

Nobuyuki Matsuki, Satoshi Shimizu, Michio Kondo, and Akihisa Matsuda

Appl. Phys. Lett. 89, 011909 (2006); http://dx.doi.org/10.1063/1.2219119 (3 pages)

Online Publication Date: 6 July 2006

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Hydrogenated amorphous silicon (a-Si:H) films prepared using a molecular beam deposition (MBD) method show an unusually sharp, narrow infrared absorption peak at 2080–2090 cm−1, which is thought to result from surface SiH species in the a-Si:H. The sharp, narrow peak is eliminated by a bias electric field of several kilovolts during deposition. The absence or presence of incoming high-energy silicon atoms or clusters accelerated by the field seems to be crucial for the resulting network structure and hydrogen distribution in a-Si:H prepared using MBD.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Method for analyzing the in-plane uniaxial anisotropy of soft magnetic thin film

Desheng Xue, Xiaolong Fan, and Changjun Jiang

Appl. Phys. Lett. 89, 011910 (2006); http://dx.doi.org/10.1063/1.2219127 (3 pages) | Cited 10 times

Online Publication Date: 6 July 2006

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Based on the vibrating sample magnetometer, a method is proposed to comprehensively analyze the in-plane uniaxial anisotropy of magnetic thin film. It can be used to determine accurately the values of effective anisotropy magnetic field Ha, anisotropy constants K1 and K2, as well as the directions of easy and hard axes. All of them can be carried out by fitting experimental M/Ms-θ0 curves with theoretical equations that only require one measurement. Using this method an effective anisotropy magnetic field Ha = 25.3 Oe and anisotropy constants K1 = 2.24×104 erg/cm3 and K2 = −4.7×103 erg/cm3 for the Co92Zr8 thin film were derived.
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75.70.Ak Magnetic properties of monolayers and thin films
07.55.Ge Magnetometers for magnetic field measurements
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
75.50.Cc Other ferromagnetic metals and alloys
75.30.Gw Magnetic anisotropy

Influence of V/III molar ratio on the formation of In vacancies in InN grown by metal-organic vapor-phase epitaxy

A. Pelli, K. Saarinen, F. Tuomisto, S. Ruffenach, and O. Briot

Appl. Phys. Lett. 89, 011911 (2006); http://dx.doi.org/10.1063/1.2219335 (3 pages) | Cited 20 times

Online Publication Date: 6 July 2006

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We have applied a slow positron beam to study InN samples grown by metal-organic vapor-phase epitaxy with different V/III molar ratios (3300–24 000) and at different growth temperatures (550–625 °C). Indium vacancies were identified in samples grown at V/III ratios below 4000. Their concentration is in the 1017cm−3 range. No strong dependence of vacancy concentration on the molar ratio was observed. At low V/III ratios, however, In droplets and vacancy clusters are formed near the substrate interface. The elevated growth temperature enhances the In vacancy formation, possibly due to limited sticking of In on the growth surface close to the decomposition temperature.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
61.72.J- Point defects and defect clusters
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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