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18 Jan 2010

Volume 96, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 033101 (2010); http://dx.doi.org/10.1063/1.3291849 (3 pages)

Ferruccio Pisanello, Luigi Martiradonna, Godefroy Leménager, Piernicola Spinicelli, Angela Fiore, Liberato Manna, Jean-Pierre Hermier, Roberto Cingolani, Elisabeth Giacobino, Massimo De Vittorio, and Alberto Bramati
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Power scaling of widely-tunable monochromatic terahertz radiation by stacking high-resistivity GaP plates

Yi Jiang, Yujie J. Ding, and Ioulia B. Zotova

Appl. Phys. Lett. 96, 031101 (2010); http://dx.doi.org/10.1063/1.3292585 (3 pages) | Cited 7 times

Online Publication Date: 19 January 2010

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A high-resistivity GaP crystal was used to generate monochromatic THz pulses with peak output powers reaching 722 W at 108.1 μm by mixing two coherent beams at about 1 μm based on phase-matched difference-frequency generation. By stacking two and three GaP plates with their second-order nonlinear coefficients being switched between the adjacent ones, we have increased the peak power at 120.3 μm from 433.4 W to 1.36 and 2.36 kW, respectively. 2.36 kW corresponds to the photon conversion efficiency of 25%, which is two orders of magnitude higher than our previous result. In contrast, if they are stacked for having the same sign of the nonlinear coefficients, the wavelength corresponding to the highest peak power is red-shifted to 204.8 and 303.9 μm, respectively. Such a result indicates that there is an optimal interaction length for each specific output wavelength.
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72.20.-i Conductivity phenomena in semiconductors and insulators
78.30.Hv Other nonmetallic inorganics

Polarization-charge tunnel junctions for ultraviolet light-emitters without p-type contact

Martin F. Schubert

Appl. Phys. Lett. 96, 031102 (2010); http://dx.doi.org/10.1063/1.3280866 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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Polarization-charge tunnel junctions for ultraviolet light-emitters (λ<360 nm) are modeled using the k⋅p multiband quantum transmitting boundary method. It is shown that polarization-charge tunnel junctions can carry sufficient current to be viable for ultraviolet emitters. Sources of inefficiency in existing ultraviolet emitters are discussed, including poor hole-injection efficiency and optical absorption in the p-type GaN contact layers. It is demonstrated that polarization-charge tunnel junctions can deliver improvements in both areas, by eliminating the need for p-type contacts, and by enabling the use of a p-side-down structure, which is shown to have favorable characteristics for carrier transport compared to conventional p-side-up structures.
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85.60.Jb Light-emitting devices

Electron acceleration in vacuum induced by a tightly focused chirped laser pulse

Jian-Xing Li (栗建兴), Wei-Ping Zang (臧维平), and Jian-Guo Tian (田建国)

Appl. Phys. Lett. 96, 031103 (2010); http://dx.doi.org/10.1063/1.3294634 (3 pages) | Cited 10 times

Online Publication Date: 19 January 2010

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Electron acceleration in vacuum induced by a tightly focused chirped laser pulse has been studied. For a fixed laser output power, the tightly focused chirped laser pulse can accelerate electrons to much higher energies. Focusing laser down to the order of wavelength requires inclusion of terms of third order at least in the diffraction angle ε in the description of the associated field. Retained electron energy depends strongly on frequency chirp parameter and initial position of the electron. Besides, retained energy increases with laser intensity, pulse duration, and initial velocity of electron, and varies periodically with laser constant phase.
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42.79.-e Optical elements, devices, and systems
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.25.Fx Diffraction and scattering

Graded photonic crystal terahertz quantum cascade lasers

Y. Chassagneux, R. Colombelli, W. Maineult, S. Barbieri, S. P. Khanna, E. H. Linfield, and A. G. Davies

Appl. Phys. Lett. 96, 031104 (2010); http://dx.doi.org/10.1063/1.3273056 (3 pages) | Cited 14 times

Online Publication Date: 20 January 2010

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The use of integrated photonic structures to tailor the behavior of light is extremely promising for optimizing performance and for introducing advanced functionalities into optoelectronic devices. We demonstrate a powerful method based on photonic-band engineering which allows the optimization of the resonator quality factors of devices operating on band-edge photonic-crystal states. We also show that carefully designed π-shifts in two-dimensional photonic-resonators give enhanced beam properties. The application of these general techniques to terahertz quantum cascade lasers yields improved maximum operating temperatures, and angularly narrow, single-lobed surface emission of ≈ 12°×8°. The devices operate at ≈2.8/2.9 THz, with peak output powers of 5 mW at 78 K.
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42.55.Px Semiconductor lasers; laser diodes
85.60.-q Optoelectronic devices

Spectral modulation of ultraviolet femtosecond laser pulse by molecular alignment of CO2, O2, and N2

Yongdong Wang, Xiaomin Dai, Jian Wu, Liang’en Ding, and Heping Zeng

Appl. Phys. Lett. 96, 031105 (2010); http://dx.doi.org/10.1063/1.3292017 (3 pages) | Cited 2 times

Online Publication Date: 20 January 2010

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We demonstrate efficient third harmonic generation of a near infrared femtosecond pulse through cascaded frequency doubling and sum-frequency generation processes, where the group velocity mismatching between the involved fundamental and generated second harmonic pulses, before they are sent to frequency mixing, are precompensated with a properly inserted nonlinear crystal. The spectrum of the generated third harmonic pulse with energy of 1.1 mJ is further modulated by using impulsive molecular alignments of CO2, O2, and N2, where significantly broadened spectrum in the ultraviolet spectral region is observed due to the additional cross-focusing effect from the parallel aligned molecules and the consequently enhanced self-phase modulation.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Mode locking of ceramic Nd:yttrium aluminum garnet with graphene as a saturable absorber

W. D. Tan, C. Y. Su, R. J. Knize, G. Q. Xie, L. J. Li, and D. Y. Tang

Appl. Phys. Lett. 96, 031106 (2010); http://dx.doi.org/10.1063/1.3292018 (3 pages) | Cited 50 times

Online Publication Date: 20 January 2010

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The mode-locking of a ceramic Nd:yttrium aluminum garnet (YAG) solid-state laser (SSL) with solution processed graphene as saturable absorber (SA) was demonstrated. Transform-limited pulses with duration of 4 ps centered at 1064 nm were generated for a nondispersion compensated Nd:YAG SSL. Z-scan studies revealed that the graphene SA has a saturation intensity of 0.87 M W cm−2 and a normalized modulation depth of 17.4%. Our results illustrate the potential of using graphene as a mode locker for SSLs.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems

Photonic crystal cavities in silicon dioxide

Yiyang Gong and Jelena Vučković

Appl. Phys. Lett. 96, 031107 (2010); http://dx.doi.org/10.1063/1.3297877 (3 pages) | Cited 15 times

Online Publication Date: 21 January 2010

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One dimensional nanobeam photonic crystal cavities fabricated in silicon dioxide are considered in both simulation and experiment. Quality factors of over 104 are found via simulation, while quality factors of over 5×103 are found in experiment, for cavities with mode volumes of 2.0(λ/n)3 and in the visible wavelength range 600–716 nm. The dependences of the cavity quality factor and mode volume for different design parameters are also considered.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials

High extraction efficiency light-emitting diodes based on embedded air-gap photonic-crystals

Elison Matioli, Elizabeth Rangel, Micheal Iza, Blaise Fleury, Nathan Pfaff, James Speck, Evelyn Hu, and Claude Weisbuch

Appl. Phys. Lett. 96, 031108 (2010); http://dx.doi.org/10.1063/1.3293442 (3 pages) | Cited 21 times

Online Publication Date: 22 January 2010

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This letter reports on high extraction efficiency light-emitting diodes (LEDs) based on embedded two-dimensional air-gap photonic crystals (PhCs). High refractive index contrast provided by the air gaps along with high interaction of the embedded PhCs with the guided light resulted in an efficient extraction of all guided modes in the LED, in contrast to the common surface PhC configuration. Embedded PhC LEDs presented an enhanced directional light emission compared to non-PhC LEDs. High extraction efficiency, close to unity, provided by the encapsulated embedded PhC LEDs demonstrates the capability of this approach to achieve high efficiency devices with directional light emission.
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85.60.Jb Light-emitting devices

Slow-light-enhanced single quantum dot emission in a unidirectional photonic crystal waveguide

S. J. Dewhurst, D. Granados, D. J. P. Ellis, A. J. Bennett, R. B. Patel, I. Farrer, D. Anderson, G. A. C. Jones, D. A. Ritchie, and A. J. Shields

Appl. Phys. Lett. 96, 031109 (2010); http://dx.doi.org/10.1063/1.3294298 (3 pages) | Cited 10 times

Online Publication Date: 22 January 2010

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We report the observation of a Purcell enhancement of the in-plane spontaneous emission rates of InAs self-assembled quantum dots coupled to a mode of a unidirectional photonic crystal waveguide fabricated in GaAs(001). Three-dimensional finite-difference time-domain simulations predict the existence of high quality-factor modes due to the slow light resonances of the waveguide. These modes have been observed experimentally with microphotoluminescence and produce enhanced in-plane emission when resonant with a quantum dot.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
42.79.Gn Optical waveguides and couplers
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials

Density-dependent carrier dynamics in a quantum dots-in-a-well heterostructure

R. P. Prasankumar, W. W. Chow, J. Urayama, R. S. Attaluri, R. V. Shenoi, S. Krishna, and A. J. Taylor

Appl. Phys. Lett. 96, 031110 (2010); http://dx.doi.org/10.1063/1.3294309 (3 pages) | Cited 2 times

Online Publication Date: 22 January 2010

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The incorporation of semiconductor quantum dots into different heterostructures for applications in nanoscale lasing and amplification has been an active area of research in recent years. Here, we use ultrafast differential transmission spectroscopy to temporally and spectrally resolve density-dependent carrier dynamics in a quantum dots-in-a-well (DWELL) heterostructure. We observe excitation-dependent shifts of the quantum dot energy levels at low densities, while at high densities we observe an anomalous induced absorption at the quantum dot excited state that is correlated with quantum well population dynamics. These studies reveal unique Coulomb interaction-induced phenomena with important implications for DWELL-based lasers and amplifiers.
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73.63.Kv Quantum dots
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)

Ring cavity induced threshold reduction in single-mode surface emitting quantum cascade lasers

Elvis Mujagić, Michele Nobile, Hermann Detz, Werner Schrenk, Jianxin Chen, Claire Gmachl, and Gottfried Strasser

Appl. Phys. Lett. 96, 031111 (2010); http://dx.doi.org/10.1063/1.3292021 (3 pages) | Cited 6 times

Online Publication Date: 22 January 2010

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We present ring cavity surface emitting (RCSE) quantum cascade lasers operating at temperatures as high as 380 K and above. A reduction in threshold current density and enhanced radiation efficiency are observed as compared to Fabry–Pérot (FP) lasers. In continuous wave, the maximum operation temperature of RCSE lasers is 50 K higher than in FP emitters. The devices exhibit single-mode emission at a wavelength around 8 μm with a side mode suppression ratio of 30 dB at room temperature. A lithographic tuning of the resonance is achieved by a variation in the grating period. The emitters exhibit a low divergent ring-shaped beam pattern with a lobe separation of ∼ 1.5°.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Mode locking of an external-cavity bisection GaInN blue-violet laser diode producing 3 ps duration optical pulses

Kyosuke Saito, Hideki Watanabe, Takao Miyajima, Masao Ikeda, and Hiroyuki Yokoyama

Appl. Phys. Lett. 96, 031112 (2010); http://dx.doi.org/10.1063/1.3292025 (2 pages) | Cited 10 times

Online Publication Date: 22 January 2010

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Passive mode locking of a bisectional GaInN quantum well laser diode was confirmed with external-cavity geometry. Optical pulses of 3 ps duration were produced by controlling the reverse-bias voltage applied to a saturable absorber section. These are the shortest optical pulses ever generated from GaN-based laser diodes.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Tailoring a plasma focus as hard x-ray source for imaging

S. Hussain, M. Shafiq, and M. Zakaullah

Appl. Phys. Lett. 96, 031501 (2010); http://dx.doi.org/10.1063/1.3291039 (3 pages) | Cited 2 times

Online Publication Date: 19 January 2010

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An investigation on temporal and spatial properties of hard x-rays (15–88 keV) emitted in a 5.3 kJ plasma focus using Si pin diodes and a pinhole camera is reported. The maximum yield of hard x-rays of 15–88 keV range is estimated about 4.7 J and corresponding efficiency for x-ray generation is 0.09%. The x-rays with energy >15 keV have 15–20 ns pulse duration and ∼ 1 mm source size. This radiation is used for contact x-ray imaging of biological and compound objects and spatial resolution of ∼ 50 μm is demonstrated.
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52.59.Px Hard X-ray sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.75.-d Plasma devices
52.77.-j Plasma applications
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Silicon-on-diamond material by pulsed laser technique

S. Lagomarsino, G. Parrini, S. Sciortino, M. Santoro, M. Citroni, M. Vannoni, A. Fossati, F. Gorelli, G. Molesini, and A. Scorzoni

Appl. Phys. Lett. 96, 031901 (2010); http://dx.doi.org/10.1063/1.3291043 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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We present a method to bond directly silicon and diamond plates to obtain a single silicon-on-diamond material, with a carbon–silicon interface of unprecedented quality. The bonding is performed at room temperature, via picosecond 355 nm pulsed laser irradiation of the silicon-diamond interface, through the transparent diamond. The obtained material exhibits excellent mechanical strength and uniformity of the bonding, as shown by mechanical tests and analysis of the cross section based on scanning electron microscopy. The bonding is ascribed to silicon carbide nanolayers at the interface which, along with amorphous silicon nanolayers, have been quantitatively detected and evaluated by means of optical spectroscopy measurements. A physical insight into the processes occurring at the diamond-silicon interface during the pulsed irradiation and cooling has been provided by a finite element numerical model. A rationale is then given for the observed SiC bond in terms of silicon and diamond melting and inter-diffusion. A crucial outcome of the model consists in predicting the effect of the different laser beam parameters on the bonding process, thereby allowing us to obtain a well tailored procedure. An excellent quality silicon-on-diamond is now available for implementing highly integrated electronic devices for diverse application areas, ranging from pixel detectors to biosensors and prostheses for the human body.
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81.20.Vj Joining; welding
68.35.Fx Diffusion; interface formation
64.70.dj Melting of specific substances
42.62.-b Laser applications
68.35.Ct Interface structure and roughness
61.46.-w Structure of nanoscale materials

Ultraviolet light emission and excitonic fine structures in ultrathin single-crystalline indium oxide nanowires

Z. P. Wei, D. L. Guo, B. Liu, R. Chen, L. M. Wong, W. F. Yang, S. J. Wang, H. D. Sun, and T. Wu

Appl. Phys. Lett. 96, 031902 (2010); http://dx.doi.org/10.1063/1.3284654 (3 pages) | Cited 10 times

Online Publication Date: 19 January 2010

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We report the ultraviolet light emission from ultrathin indium oxide (In2O3) nanowires fabricated by the vapor-liquid-solid method. The high crystalline quality of the samples is confirmed by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Strong ultraviolet light emission is consistently observed in the temperature dependent photoluminescence measurements carried out between 10 and 300 K. Emissions related to free excitons and bound exciton complexes, donor-acceptor pair transition and its relevant longitudinal optical phonon replicas are identified and their temperature-dependent evolution is discussed in details.
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71.35.-y Excitons and related phenomena
81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
78.40.Fy Semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.67.Uh Nanowires

Formation, structure, and electric property of CaB4 single crystal synthesized under high pressure

Zhongyuan Liu, Xianyue Han, Dongli Yu, Yaxin Sun, Bo Xu, Xiang-Feng Zhou, Julong He, Hui-Tian Wang, and Yongjun Tian

Appl. Phys. Lett. 96, 031903 (2010); http://dx.doi.org/10.1063/1.3293451 (3 pages) | Cited 5 times

Online Publication Date: 19 January 2010

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Via the combination of theoretical and experimental investigations, we have synthesized the single crystal of pure calcium tetraboride (CaB4) under the conditions of high pressure and high temperature. The Temperature (T)-Pressure (P) phase diagram of Ca–B binary system has been obtained. The recovered CaB4 after decompression of high pressure is characterized to have a ThB4-type tetragonal structure. Both the calculated band structure and the measured temperature-dependent resistivity are indicative of the intrinsic metallic property of CaB4, contrary to the hypothetical semiconducting behavior.
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61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)
81.30.Dz Phase diagrams of other materials
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
71.15.-m Methods of electronic structure calculations
62.50.-p High-pressure effects in solids and liquids

Polariton effects in the dielectric function of ZnO excitons obtained by ellipsometry

Munise Cobet, Christoph Cobet, Markus R. Wagner, Norbert Esser, Christian Thomsen, and Axel Hoffmann

Appl. Phys. Lett. 96, 031904 (2010); http://dx.doi.org/10.1063/1.3284656 (3 pages) | Cited 7 times

Online Publication Date: 19 January 2010

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The complex dielectric tensor of ZnO in the regime of the excitonic transitions is determined with ellipsometry and analyzed concerning the quantization of the electromagnetic field in terms of coupled polariton-eigenmodes. Negative sections in the real part indicate the significant formation of polaritons for the dipole-allowed excitons of the three upper valence-bands Γ7,Γ9,Γ7. The transverse-longitudinal splittings which separate the upper polariton branch from the lower branch, corresponding to the k-vector of the used light, are deduced precisely for each subband. Mainly for E∥c, additional absorption peaks are observed at the longitudinal B-exciton and closely above. One is considered to be a mixed-mode and the other is seen as a consequence of interference effects in an exciton free surface layer which is also visible in reflectance anisotropy spectroscopy.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
73.20.At Surface states, band structure, electron density of states
71.35.-y Excitons and related phenomena
07.60.Fs Polarimeters and ellipsometers

Enhancement of plastic deformability in Fe–Ni–Nb–B bulk glassy alloys by controlling the Ni-to-Fe concentration ratio

J. M. Park, G. Wang, R. Li, N. Mattern, J. Eckert, and D. H. Kim

Appl. Phys. Lett. 96, 031905 (2010); http://dx.doi.org/10.1063/1.3291668 (3 pages) | Cited 13 times

Online Publication Date: 19 January 2010

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The influence of partial replacement of Fe by Ni in (Fe1−xNix)71Nb6B23 (0 ≤ x ≤ 0.5) bulk glassy alloys on the enhancement of the plasticity has been investigated. The increase of the Ni-to-Fe concentration ratio effectively improves the compressive plasticity. The (Fe0.5Ni0.5)71Nb6B23 alloy exhibits an enhanced plastic strain of ∼ 4.2%, together with high strength and distinct strain hardeninglike characteristics, when compared with the Ni-free Fe71Nb6B23 glass. The improved mechanical properties are ascribed to the control of the intrinsic elastic properties, followed by favorably tuning the interatomic interaction.
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81.40.Lm Deformation, plasticity, and creep
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.fq Plasticity and superplasticity
62.20.D- Elasticity

Carrier localization and nonradiative recombination in yellow emitting InGaN quantum wells

T. Li, A. M. Fischer, Q. Y. Wei, F. A. Ponce, T. Detchprohm, and C. Wetzel

Appl. Phys. Lett. 96, 031906 (2010); http://dx.doi.org/10.1063/1.3293298 (3 pages) | Cited 10 times

Online Publication Date: 20 January 2010

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InGaN quantum wells, with luminescence in the yellow region of the visible spectrum, have been studied using conventional and time-resolved cathodoluminescence. We observe the absence of strong localization effects and a relatively high internal quantum efficiency of ∼ 12%, which are unexpected for InGaN in this-long wavelength emission range. We have also observed a steady decrease of the peak emission energy, and a continuous increase in the radiative recombination lifetime with temperature up to 100 K. These two features are manifestations of recombination due to nonlocalized excitons. Nonradiative recombination centers, with activation energy of ∼ 6 meV, appear to constitute the main mechanism limiting the internal quantum efficiency of these films.
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78.67.De Quantum wells
71.35.-y Excitons and related phenomena
78.60.Hk Cathodoluminescence, ionoluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Hs Quantum wells
78.40.Fy Semiconductors

H-induced subcritical crack propagation and interaction phenomena in (001) Si using He-cracks templates

S. Reboh, J. F. Barbot, M. F. Beaufort, and P. F. P. Fichtner

Appl. Phys. Lett. 96, 031907 (2010); http://dx.doi.org/10.1063/1.3290249 (3 pages) | Cited 5 times

Online Publication Date: 21 January 2010

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H and He ion implantations allow the formation of nanocracks within controlled subsurface depths in semiconducting materials. Upon annealing, crack propagation and coalescence provides a way of cutting monocrystalline thin films. Here, the mechanisms of coalescence by crack-tip interactions are depicted in (001) Si wafers. Starting from overpressurized He-cracks, subcritical propagation was activated by diffusional H. Nanocrack interaction can occur by elastic forces, causing tip folding, or by plastic deformation forming extended defects. These observations are discussed and modeled using elasticity and fracture mechanics. The model suggests that kinetic effects in the cutting process depend on the crack interplanar separations.
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62.20.mt Cracks
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
66.30.J- Diffusion of impurities
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
61.72.uf Ge and Si
81.40.Lm Deformation, plasticity, and creep

Enhancing erbium emission by strain engineering in GaN heteroepitaxial layers

I. W. Feng, J. Li, A. Sedhain, J. Y. Lin, H. X. Jiang, and J. Zavada

Appl. Phys. Lett. 96, 031908 (2010); http://dx.doi.org/10.1063/1.3295705 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2010

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Much research has been devoted to the incorporation of erbium (Er) into semiconductors aimed at achieving photonic integrated circuits with multiple functionalities. GaN appears to be an excellent host material for Er ions due to its structural and thermal stability. Er-doped GaN (GaN:Er) epilayers were grown on different templates, GaN/Al2O3, AlN/Al2O3, GaN/Si (111), and c-GaN bulk. The effects of stress on 1.54 μm emission intensity, caused by lattice mismatch between the GaN:Er epilayer and the substrate, were probed. The emission intensity at 1.54 μm increased with greater tensile stress in the c-direction of the GaN:Er epilayers. These results indicate that the characteristics of photonic devices based on GaN:Er can be optimized through strain engineering.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors

Sol-gel deposition and piezoelectric properties of {110}-oriented Pb(Zr0.52Ti0.48)O3 thin films

D. Ambika, Viswanathan Kumar, Hideyuki Imai, and Isaku Kanno

Appl. Phys. Lett. 96, 031909 (2010); http://dx.doi.org/10.1063/1.3293446 (3 pages) | Cited 4 times

Online Publication Date: 22 January 2010

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Pb(ZrxTi1−x)O3 [PZT] thin films of thickness 2.0 μm were fabricated on silicon substrates (111)Pt/Ti/SiO2/Si using a sol-gel spin-coating technique. PZT films on substrates with a strontium titanate bottom layer are preferentially {110}-oriented with a columnar structure. The PZT films exhibit good dielectric properties with a dielectric permittivity, εr = 1545 and dielectric loss, tan δ = 0.04. Excellent piezoelectric characteristics are also exhibited by the {110}-oriented films with an average effective transverse piezocoefficient, e31∗ of −8.4 C/m2. The influence of film texture and composition on the transverse piezocoefficient have also been studied.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.jm Texture
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.65.-j Piezoelectricity and electromechanical effects
77.84.Cg PZT ceramics and other titanates
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
77.55.hj PZT

SrxBa1−xNb2O6−δ Ferroelectric-thermoelectrics: Crystal anisotropy, conduction mechanism, and power factor

Soonil Lee, Rudeger H. T. Wilke, Susan Trolier-McKinstry, Shujun Zhang, and Clive A. Randall

Appl. Phys. Lett. 96, 031910 (2010); http://dx.doi.org/10.1063/1.3291563 (3 pages) | Cited 5 times

Online Publication Date: 22 January 2010

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Nonstoichiometric tungsten bronze-structured ferroelectric SrxBa1−xNb2O6−δ (SBN) single crystals were found to be a promising n-type thermoelectric oxide. Thermopower anomalies were observed at the phase transition temperatures, depending on the degree of reduction as well as crystal anisotropy. Above 500 K, heavily reduced SBN crystals show high thermoelectric power factors ( ∼ 20 μW/cm K2 at 516 K) with both thermopower and electrical conductivity higher parallel to the c-axis. It is noted that the power factor increases with temperature due to the semiconducting behavior with high carrier concentration. The carrier transport mechanism also varies with the degree of reduction and temperature.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.20.-i Conductivity phenomena in semiconductors and insulators
75.30.Gw Magnetic anisotropy
77.80.-e Ferroelectricity and antiferroelectricity

Surface-energy triggered phase formation and epitaxy in nanometer-thick Ni1−xPtx silicide films

Jun Luo, Zhijun Qiu, Chaolin Zha, Zhen Zhang, Dongping Wu, Jun Lu, Johan Åkerman, Mikael Östling, Lars Hultman, and Shi-Li Zhang

Appl. Phys. Lett. 96, 031911 (2010); http://dx.doi.org/10.1063/1.3291679 (3 pages) | Cited 9 times

Online Publication Date: 22 January 2010

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The formation of ultrathin silicide films of Ni1−xPtx at 450–850 °C is reported. Without Pt (x = 0) and for tNi<4 nm, epitaxially aligned NiSi2−y films readily grow and exhibit extraordinary morphological stability up to 800 °C. For tNi ≥ 4 nm, polycrystalline NiSi films form and agglomerate at lower temperatures for thinner films. Without Ni (x = 1) and for tPt = 1–20 nm, the annealing behavior of the resulting PtSi films follows that for the NiSi films. The results for Ni1−xPtx of other compositions support the above observations. Surface energy is discussed as the cause responsible for the distinct behavior in phase formation and morphological stability.
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65.40.gp Surface energy
61.46.-w Structure of nanoscale materials
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.55.J- Morphology of films
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Electronic band structure information of GdN extracted from x-ray absorption and emission spectroscopy

A. R. H. Preston, B. J. Ruck, W. R. L. Lambrecht, L. F. J. Piper, J. E. Downes, K. E. Smith, and H. J. Trodahl

Appl. Phys. Lett. 96, 032101 (2010); http://dx.doi.org/10.1063/1.3291057 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2010

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The electronic structure of GdN films grown by pulsed laser deposition has been investigated by soft x-ray absorption (XAS) and x-ray emission spectroscopy (XES) at the N K-edge. Density functional calculations within the local spin density approximation with Hubbard-U corrections of the N p weighted bands and density of states are used to extract band information from the spectra. Gd M4,5 XAS and XES spectra are also presented. The XES-XAS separation is shown to give information on the f-band spin splitting and the XAS line shapes are shown to reflect atomic multiplet effects.
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78.70.Dm X-ray absorption spectra
71.20.-b Electron density of states and band structure of crystalline solids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.10.Fd Lattice fermion models (Hubbard model, etc.)
81.15.Fg Pulsed laser ablation deposition
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