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16 Jan 2012

Volume 100, Issue 3, Articles (03xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 033109 (2012); http://dx.doi.org/10.1063/1.3664636 (3 pages)

Sang H. Yun, Hyung-Seok Lee, Young Ha Kwon, Mats Göthelid, Sang Mo Koo, Lars Wågberg, Ulf O. Karlsson, and Jan Linnros
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A tapered parallel-plate-waveguide probe for THz near-field reflection imaging

Jingbo Liu, Rajind Mendis, Daniel M. Mittleman, and Naokazu Sakoda

Appl. Phys. Lett. 100, 031101 (2012); http://dx.doi.org/10.1063/1.3677678 (3 pages) | Cited 5 times

Online Publication Date: 17 January 2012

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We demonstrate a broad-band low-loss THz near-field imaging technique based on a tapered parallel-plate waveguide. This technique works in a reflection geometry, which avoids the problem of low energy throughput due to the impedance mismatch and consequently limited spatial resolution, in the transmission geometry. Images reconstructed by the filtered-back-projection algorithm are able to resolve features of size ∼100 μm using radiation with an average wavelength of 1.5 mm.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.30.Va Image forming and processing
42.30.Wb Image reconstruction; tomography

Self-assembled broadband plasmonic nanoparticle arrays for sensing applications

R. Verre, K. Fleischer, O. Ualibek, and I. V. Shvets

Appl. Phys. Lett. 100, 031102 (2012); http://dx.doi.org/10.1063/1.3674982 (3 pages) | Cited 4 times

Online Publication Date: 17 January 2012

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Highly ordered noble metal nanoparticle (NP) arrays are produced using a glancing angle deposition on stepped substrates. The versatility of the technique is demonstrated by depositing different metals, resulting in shifts of the resonance positions. The behaviour of the NP arrays grown is predicted by a dipolar model, and it is measured using reflectance anisotropy spectroscopy (RAS). Fine tuning of the resonances can be finally realised by selecting the deposition parameters. The combined application of both RAS and deposition at glancing angles provides a unique tool to grow NP arrays with the tunable plasmonic resonances in the entire visible range.
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81.16.Dn Self-assembly
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.Bz Metals and metallic alloys

Low-voltage driven visible and infrared electroluminescence from light-emitting device based on Er-doped TiO2/p+-Si heterostructure

Yang Yang, Lu Jin, Xiangyang Ma, and Deren Yang

Appl. Phys. Lett. 100, 031103 (2012); http://dx.doi.org/10.1063/1.3678026 (4 pages) | Cited 5 times

Online Publication Date: 18 January 2012

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We report on visible and infrared electroluminescence (EL) from the light-emitting device based on Er-doped TiO2/p+-Si heterostructure. Under a forward bias voltage as low as 5.5 V, the device emits ∼1540 nm infrared light and visible light peaking at 522, 553, 564, and 663 nm, respectively, which are originated from Er3+ intra-4f transitions. It is found that the existence of sufficient oxygen vacancies in TiO2 is critical for triggering the Er-related EL. Furthermore, the energy transfer from the oxygen-vacancy-related excitons in TiO2 matrix to Er3+ ions is supposed to be responsible for the above-mentioned EL.
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85.60.Jb Light-emitting devices

Fabrication of nanometer-size structures in metal thin films using femtosecond laser Bessel beams

B. Yalizay, T. Ersoy, B. Soylu, and S. Akturk

Appl. Phys. Lett. 100, 031104 (2012); http://dx.doi.org/10.1063/1.3678030 (3 pages) | Cited 3 times

Online Publication Date: 18 January 2012

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We report nanometer-scale fabrication on metal thin films using ablation by femtosecond laser pulses, with Bessel beam profiles. Choosing the laser fluence around ablation threshold allows control of the structure size below the diffraction limit. We show that using Bessel beams has several advantages. Bessel beams have focal spot sizes insensitive to longitudinal position, which significantly relaxes alignment constraints. Tighter foci are easier to generate, less costly, and less prone to aberrations. Scaling the method to shorter wavelengths, and hence increasing the resolution is also straightforward. By using the proposed method, we generate structures with resolution below 200 nm.
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42.62.-b Laser applications
42.82.Cr Fabrication techniques; lithography, pattern transfer
68.55.-a Thin film structure and morphology
81.16.-c Methods of micro- and nanofabrication and processing

Improvement of hole injection and electron overflow by a tapered AlGaN electron blocking layer in InGaN-based blue laser diodes

Wei Yang, Ding Li, Ningyang Liu, Zhao Chen, Lei Wang, Lei Liu, Lei Li, Chenghao Wan, Weihua Chen, Xiaodong Hu, and Weimin Du

Appl. Phys. Lett. 100, 031105 (2012); http://dx.doi.org/10.1063/1.3678197 (5 pages) | Cited 2 times

Online Publication Date: 18 January 2012

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We studied the influence of a tapered AlGaN electron blocking layer (EBL) with step-graded aluminum composition on hole injection and electron overflow effects in InGaN-based laser diodes (LDs) theoretically. Schrödinger-Poisson self-consistent method together with transfer matrix method was applied to calculate carrier distribution and transport properties for both electrons and holes in tapered EBL and conventional EBL. The results indicate that the new structure favors the tunneling of low energy holes from the p-side to the active region. Meanwhile, more uniform carrier distribution and better balance between electrons and holes are obtained for the tapered structure by proper modification of band diagrams. An advanced device simulation shows the elimination of electron overflow even at a current of 180 mA in the LD with tapered EBL. Decrease of threshold current density from 2.0 kA/cm2 to 1.6 kA/cm2 is benefited from the more uniform local gain profile.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultrafast all-optical tunable Fano resonance in nonlinear ferroelectric photonic crystals

Yingbo Zhang, Xiaoyong Hu, Yulan Fu, Hong Yang, and Qihuang Gong

Appl. Phys. Lett. 100, 031106 (2012); http://dx.doi.org/10.1063/1.3678184 (4 pages) | Cited 5 times

Online Publication Date: 19 January 2012

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We report an ultrafast all-optical tunable Fano resonance in a nonlinear ferroelectric photonic crystal made of polycrystal lithium niobate, which provides a large nonlinear susceptibility because of strong quantum size effect of nanoscale crystal grains. The femtosecond pump and probe method is adopted to measure the tunability of the Fano resonance based on the nonlinear optical Kerr effect. A 37-nm shift in the Fano resonance wavelength is obtained under excitation of a 30 MW/cm2 pump laser. An ultrafast response time of 43 ps is achieved due to fast relaxation dynamics of bound electrons in polycrystal lithium niobate.
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42.70.Qs Photonic bandgap materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

High-power laterally coupled distributed-feedback GaSb-based diode lasers at 2 μm wavelength

Siamak Forouhar, Ryan M. Briggs, Clifford Frez, Kale J. Franz, and Alexander Ksendzov

Appl. Phys. Lett. 100, 031107 (2012); http://dx.doi.org/10.1063/1.3678187 (4 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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We report on GaSb-based laterally coupled distributed-feedback (DFB) diode lasers designed to operate at wavelengths near 2.05 μm. Second-order Bragg gratings were etched alongside narrow ridge waveguides to enable single-mode DFB operation in 2-mm-long laser diodes. At a heat-sink temperature of 10 °C, the lasers emit more than 40 mW continuous-wave in a single longitudinal mode, while increasing the current beyond 300 mA results in multimode operation due to spectral shifting of the laser gain with respect to the peak grating reflectivity. At −10 °C, we observe DFB operation at higher current, with single-facet emission exceeding 80 mW.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Thermal resistance reduction in high power superluminescent diodes by using active multi-mode interferometer

Zhigang Zang, Keisuke Mukai, Paolo Navaretti, Marcus Duelk, Christian Velez, and Kiichi Hamamoto

Appl. Phys. Lett. 100, 031108 (2012); http://dx.doi.org/10.1063/1.3678188 (4 pages) | Cited 29 times

Online Publication Date: 19 January 2012

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Low thermal resistance of high power superluminescent diodes (SLEDs) by using active multi-mode interferometer (active-MMI) is presented in this paper. The active layer temperature evaluation demonstrates that the power saturation mechanism in active-MMI SLED is heat for the first time. Low thermal resistance of 4.83 K/W in active-MMI SLEDs leads to a high power of 115 mW. Moreover, the effect of the active area size on the output power is demonstrated both experimentally and theoretically. Good agreement between the theoretical and experimental results indicates that active-MMI configuration is a new design in support of efficient heat dissipation and thermal resistance reduction for SLEDs.
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85.60.Jb Light-emitting devices

Semiconductor disk laser at 2.05 μm wavelength with <100 kHz linewidth at 1 W output power

Sebastian Kaspar, Marcel Rattunde, Tino Töpper, Christian Manz, Klaus Köhler, and Joachim Wagner

Appl. Phys. Lett. 100, 031109 (2012); http://dx.doi.org/10.1063/1.3675637 (3 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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We report on an optically pumped single-mode GaSb-based semiconductor disk laser (SDL) emitting at 2.05 μm at an output power of 960 mW (1100 mW) with a side-mode suppression of better than 30 dB (20 dB). A linewidth of 60 kHz (sampling time: 100 μs) was measured at an output power of 960 mW. This improvement in output power over previous reports, which was achieved via a careful design of the SDL cavity paying close attention to the spatial overlap between cavity mode and pump spot, makes this class of SDL particularly attractive for remote sensing and optical free-space communication.
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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

Microwire (Mg,Zn)O/ZnO and (Mg,Zn)O/(Cd,Zn)O non-polar quantum well heterostructures for cavity applications

C. P. Dietrich, M. Lange, M. Stölzel, and M. Grundmann

Appl. Phys. Lett. 100, 031110 (2012); http://dx.doi.org/10.1063/1.3678594 (4 pages) | Cited 3 times

Online Publication Date: 19 January 2012

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Pulsed-laser deposited, non-polar MgxZn1−xO/ZnO and MgxZn1−xO/Zn1−yCdyO quantum well heterostructures were fabricated in radial direction on ZnO microwires with well-defined hexagonal cross section. Optical resonances modulate room-temperature luminescence spectra for all fabricated heterostructures demonstrating their applicability as microcavities. Quantum confinement was proven by time-integrated and time-resolved luminescence. The ZnO quantum well emission was tuned between 3.76 and 3.35 eV by adjusting the well thickness and barrier composition. In order to further reduce the QW emission energy, active Zn1−yCdyO quantum wells in MgxZn1−xO barriers were grown emitting between 3.07 and 2.70 eV for different well thicknesses but fixed barrier composition.
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42.79.-e Optical elements, devices, and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
06.60.Vz Workshop procedures (welding, machining, lubrication, bearings, etc.)

Room temperature, continuous wave lasing in microcylinder and microring quantum dot laser diodes

M. Munsch, J. Claudon, N. S. Malik, K. Gilbert, P. Grosse, J.-M. Gérard, F. Albert, F. Langer, T. Schlereth, M. M. Pieczarka, S. Höfling, M. Kamp, A. Forchel, and S. Reitzenstein

Appl. Phys. Lett. 100, 031111 (2012); http://dx.doi.org/10.1063/1.3678031 (4 pages) | Cited 1 time

Online Publication Date: 20 January 2012

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We demonstrate room temperature, continuous wave lasing of laser diodes based on AlGaAs whispering gallery mode (WGM) resonators (microcylinder and microring) embedding a quantum dot (QD) active layer. Using InGaAlAs QDs, high-Q (>60 000) lasing modes are observed around 910 nm, up to 50 °C. Lasing with similar performance is obtained around 1230 nm, using InAs QDs. Furthermore, we show that the current injection in the active part of the device is improved in ring resonators, leading to threshold currents of approximately 4 mA for a device with 80 μm diameter. This geometry also suppresses WGMs with a high radial order, thus simplifying the lasing spectra. In these conditions, stable single-mode and two-color lasing can be obtained.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Advantages of blue InGaN light-emitting diodes with InGaN-AlGaN-InGaN barriers

Yen-Kuang Kuo, Tsun-Hsin Wang, and Jih-Yuan Chang

Appl. Phys. Lett. 100, 031112 (2012); http://dx.doi.org/10.1063/1.3678341 (3 pages) | Cited 3 times

Online Publication Date: 20 January 2012

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Efficiency enhancement of the blue InGaN light-emitting diodes (LEDs) with InGaN-AlGaN-InGaN barriers is studied numerically. The energy band diagrams, carrier concentrations in quantum wells, radiative recombination rate in active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results suggest that the blue InGaN/InGaN-AlGaN-InGaN LED has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams, which are caused mainly by the reduced polarization charges at the interface between the well and barrier.
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85.60.Jb Light-emitting devices

Enhancement of light-extraction efficiency of SiNx light emitting devices through a rough Ag island film

Feng Wang, Dongsheng Li, Deren Yang, and Duanlin Que

Appl. Phys. Lett. 100, 031113 (2012); http://dx.doi.org/10.1063/1.3678632 (4 pages) | Cited 11 times

Online Publication Date: 20 January 2012

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Based on an ITO/Ag/SiNx/p+-Si/Al structure, a significant enhancement of the external quantum efficiency was achieved compared with the device without Ag island film. Analysis showed that the increase of the light-extraction efficiency resulted from the surface roughening of ITO electrode has a main contribution to this enhancement. The increase of the internal quantum efficiency induced by the enhancement of spontaneous emission rate and the carrier injection level also has an instructive contribution. Our results demonstrate that localized surface plasmons enhanced SiNx-based light emitting devices show great promise for the development of efficiency Si-based optical device.
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85.60.Jb Light-emitting devices
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Morphology control of Fe films using ordered termination on SrTiO3 surfaces

TeYu Chien (簡德宇), John W. Freeland, and Nathan P. Guisinger

Appl. Phys. Lett. 100, 031601 (2012); http://dx.doi.org/10.1063/1.3679177 (4 pages) | Cited 1 time

Online Publication Date: 18 January 2012

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Long-range nanometer-scale stripe patterns of alternating termination on fractured Nb-doped SrTiO3 surfaces were used as templates to control the Fe film morphology. The as deposited Fe film consisted of a uniform layer of small Fe clusters (∼4 nm) randomly distributed on the surface. After annealing, two distinct morphologies were formed and were directly correlated to the underlying SrO and TiO2 terminated stripes. This behavior is consistent with a higher interfacial energy of the Fe/SrO interface than that of the Fe/TiO2 interface.
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68.55.at Other materials
65.40.gp Surface energy
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Ultrabroadband terahertz spectroscopy of chalcogenide glasses

Maksim Zalkovskij, Christer Zoffmann Bisgaard, Andrey Novitsky, Radu Malureanu, Dan Savastru, Aurelian Popescu, Peter Uhd Jepsen, and Andrei V. Lavrinenko

Appl. Phys. Lett. 100, 031901 (2012); http://dx.doi.org/10.1063/1.3676443 (4 pages) | Cited 4 times

Online Publication Date: 17 January 2012

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Chalcogenide glasses are receiving a lot of attention due to their unique optical properties. In this paper we study the optical properties of As2S3 and GaLaS glasses in a broad terahertz (THz) frequency range (0.2-18 THz). Complex dispersion behavior with drastic changes of refractive index and absorption coefficient is found for both glasses. We observe the breakdown of the universal power-law dependence of the absorption coefficient due to atomic vibrations observed at low THz frequencies in disordered materials, and see the transition to localized vibrational dynamics for the As2S3 compound at higher frequencies. In addition, As2S3 displays two transparency regions, at 7-8 THz and 12.2 THz, of potential interest for future nonlinear applications in the THz range.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
78.66.Jg Amorphous semiconductors; glasses

Tuning of nonlinear vibration via topology variation and its application in energy harvesting

Xuhan Dai, Xiaodan Miao, Linghe Sui, Hailin Zhou, Xiaolin Zhao, and Guifu Ding

Appl. Phys. Lett. 100, 031902 (2012); http://dx.doi.org/10.1063/1.3676661 (4 pages) | Cited 1 time

Online Publication Date: 17 January 2012

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A topology variation method for the tuning of nonlinear vibration of planar spring was proposed and experimentally validated, which exhibited great potential for the application of energy harvesting by broadening the response bandwidth of the device. According to the numerical simulation and experimental results of all the three typical topological configurations, the topological scheme with inclined straight shape could provide the best nonlinearity. When this method was applied to the energy harvesting, the prototype device demonstrated a bandwidth of 28 Hz @180 Hz. It is concluded that the topological variation methodology could be efficient for the performance optimization of the energy harvester.
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84.60.Bk Performance characteristics of energy conversion systems; figure of merit

On the entanglement of electrostriction and non-linear piezoelectricity in non-centrosymmetric materials

L. Pedesseau, C. Katan, and J. Even

Appl. Phys. Lett. 100, 031903 (2012); http://dx.doi.org/10.1063/1.3676666 (4 pages) | Cited 3 times

Online Publication Date: 17 January 2012

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An extended and complete thermodynamical model of third-order electro-elastic coupling is proposed with symmetry analyses and density functional theory (DFT) calculations to evaluate consistently the various linear and non-linear coefficients. It is shown that in non-centrosymmetric materials, electrostrictive and non-linear piezoelectric phenomena are strongly coupled, except for materials crystallizing in a cubic lattice associated to the 432 point group. Thorough numerical results are given for GaN and AlN compounds in the Würtzite structure. Electrostriction dominates, but non-linear elasticity and non-linear piezoelectricity must be taken into account for strain evaluation whereas non-linear piezoelectricity yields a significant correction for electric field.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Epitaxial graphene on SiC(000math): Stacking order and interfacial structure

Xiaojun Weng, Joshua A. Robinson, Kathleen Trumbull, Randall Cavalero, Mark A. Fanton, and David Snyder

Appl. Phys. Lett. 100, 031904 (2012); http://dx.doi.org/10.1063/1.3678021 (4 pages) | Cited 1 time

Online Publication Date: 18 January 2012

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The fundamental structural properties of multilayer epitaxial graphene (MEG) on C-face SiC(000math) were revealed in a straightforward manner using cross-sectional transmission electron microscopy (TEM) and scanning TEM (STEM). The AB-stacking and the azimuthal rotational disorder of the graphene layers were directly identified by selected area electron diffraction and high-resolution TEM. The directly interpretable STEM revealed that the interlayer spacing between the first graphene layer and the top SiC bilayer is substantially larger than that of the bulk graphite. Such a large interlayer spacing combined with the regional partially decomposed top bilayers of the SiC substrate provides a plausible explanation to the weak bonding between the MEG film and the SiC(000math) substrate.
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61.48.Gh Structure of graphene
68.55.-a Thin film structure and morphology
68.65.Ac Multilayers

Experimental determination of current spill-over and its effect on the efficiency droop in InGaN/GaN blue-light-emitting-diodes

Byung-Jun Ahn, Tae-Soo Kim, Yanqun Dong, Moon-Taek Hong, Jung-Hoon Song, Jae-Ho Song, Hwan-Kuk Yuh, Sung-Chul Choi, Duk-Kyu Bae, and Youngboo Moon

Appl. Phys. Lett. 100, 031905 (2012); http://dx.doi.org/10.1063/1.3678029 (4 pages) | Cited 8 times

Online Publication Date: 18 January 2012

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We report the experimental determination of current spill-over in InGaN/GaN blue light emitting diodes by measuring the change in the forward current generated by a resonant excitation. To quantify accurately, the absorption of the laser as a function of the forward current was also determined. Two samples that have clearly different behavior of efficiency droop were compared to clarify the relationship between the current spill-over and the efficiency droop. We conclude that the carrier spill-over does occur and can be a significant cause for the efficiency droop but cannot single-handedly account for the efficiency droop.
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85.60.Jb Light-emitting devices
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Measurement of heavy-hole spin dephasing in (InGa)As quantum dots

R. Dahbashi, J. Hübner, F. Berski, J. Wiegand, X. Marie, K. Pierz, H. W. Schumacher, and M. Oestreich

Appl. Phys. Lett. 100, 031906 (2012); http://dx.doi.org/10.1063/1.3678182 (4 pages) | Cited 9 times

Online Publication Date: 19 January 2012

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We measure the spin dephasing of holes localized in self-assembled (InGa)As quantum dots by spin noise spectroscopy. The localized holes show a distinct hyperfine interaction with the nuclear spin bath despite the p-type symmetry of the valence band states. The experiments reveal a short spin relaxation time τfasthh of 27 ns and a second, long spin relaxation time τslowhh which exceeds the latter by more than one order of magnitude. The two times are attributed to heavy-hole spins aligned perpendicular and parallel to the stochastic nuclear magnetic field. Intensity dependent measurements and numerical simulations reveal that the long relaxation time is still obscured by light absorption, despite low laser intensity and large detuning. Off-resonant light absorption causes a suppression of the spin noise signal due to the creation of a second hole entailing a vanishing hole spin polarization.
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72.25.Dc Spin polarized transport in semiconductors
73.21.La Quantum dots
76.60.Es Relaxation effects
78.67.Hc Quantum dots
71.20.Nr Semiconductor compounds
71.70.Jp Nuclear states and interactions

The relationship between structural evolution and electrical percolation of the initial stages of tungsten chemical vapor deposition on polycrystalline TiN

A. Rozenblat, S. Haimson, Y. Shacham-Diamand, and D. Horvitz

Appl. Phys. Lett. 100, 031907 (2012); http://dx.doi.org/10.1063/1.3678194 (4 pages)

Online Publication Date: 20 January 2012

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This paper presents experimental results and a geometric model of the evolution of sheet resistance and surface morphology during the transition from nucleation to percolation of tungsten chemical vapor deposition over ultrathin polycrystalline titanium nitride (TiN). We observed two mechanisms of reduction in sheet resistance. At deposition temperatures higher than 310 °C, percolation effect is formed at ∼35% of surface coverage, θ, and characterized with a sharp drop in resistance. At temperature below 310 °C, a reduction in resistance occurs in two steps. The first step occurs when θ = 35% and the second step at θ = 85%. We suggest a geometric model in which the electrical percolation pass is modulated by the thickness threshold of the islands at the instant of collision.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.60.qj Studies of nucleation in specific substances
68.35.bd Metals and alloys
68.55.at Other materials
73.61.At Metal and metallic alloys
81.05.Bx Metals, semimetals, and alloys

Below band-gap optical absorption and photoluminescence excitation spectroscopy at room temperature in low-defect-density bulk GaN:Fe

P. Gladkov, E. Hulicius, T. Paskova, E. Preble, and K. R. Evans

Appl. Phys. Lett. 100, 031908 (2012); http://dx.doi.org/10.1063/1.3678195 (3 pages)

Online Publication Date: 20 January 2012

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We present a detailed study of the below band-gap optical absorption at room temperature in bulk semi-insulating GaN:Fe versus the Fe-doping. It was established that the 1.24 eV photoluminescence band at 300 K consists of only vibrational replicas of the Fe3+ 4T1(G)→6A1(S) internal transition. We also studied the below band-gap photoluminescence excitation of the 1.24 eV band. The identical exponential rise of the photoluminescence excitation and the optical absorption coefficient identify the Fe3+/2+ charge-transfer as the main contributor to the 300 K optical absorption in the range 400-500 nm. Practical implications of these results for Fe-doping determination are discussed.
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78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Temperature dependence of current conduction in semi-insulating 4H-SiC epitaxial layer

Peter G. Muzykov, Ramesh M. Krishna, and Krishna C. Mandal

Appl. Phys. Lett. 100, 032101 (2012); http://dx.doi.org/10.1063/1.3676270 (4 pages) | Cited 2 times

Online Publication Date: 17 January 2012

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We have investigated temperature dependence (94 K–650 K) of current conduction in semi-insulating 4H-SiC epitaxial layer. The epitaxial layer was grown on highly doped n-type (0001) 4H-SiC substrate using chemical vapor deposition with dichlorosilane precursor. The current—voltage (I-V) characteristics exhibited steps at ∼1 V and ∼70 V that were attributed to the filling of deep level centers by injected electrons. Correlation of the I-V characteristics with the results of thermally stimulated current measurements showed that deep centers peaked at 242 K, 285 K, and 500 K, were responsible for the steps in the I-V characteristics. Slow processes of the injected carrier capture on traps resulted in the I-V characteristic with negative differential resistance.
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73.61.Le Other inorganic semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
71.55.Ht Other nonmetals
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Metal insulator transition with ferrimagnetic order in epitaxial thin films of spinel NiCo2O4

Punam Silwal, Ludi Miao, Ilan Stern, Xiaolan Zhou, Jin Hu, and Dae Ho Kim

Appl. Phys. Lett. 100, 032102 (2012); http://dx.doi.org/10.1063/1.3676439 (3 pages)

Online Publication Date: 17 January 2012

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We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.
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71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials

Surface transfer doping of diamond with a molecular heterojunction

D. P. Langley, Y. Smets, C. B. Stark, M. T. Edmonds, A. Tadich, K. J. Rietwyk, A. Schenk, M. Wanke, Q.-H. Wu, P. J. Barnard, L. Ley, and C. I. Pakes

Appl. Phys. Lett. 100, 032103 (2012); http://dx.doi.org/10.1063/1.3676445 (4 pages) | Cited 3 times

Online Publication Date: 17 January 2012

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Surface conductivity and C1s core level measurements were employed to show that surface transfer doping of hydrogen-terminated diamond C(100) can be achieved with a molecular heterojunction formed with C60F48 and an intralayer of zinc-tetraphenylporphyrin. Measurement of the shift in the diamond Fermi energy shows that the zinc-tetraphenylporphyrin (ZnTPP) layer modifies the C60F48–diamond interaction, modulating the extent of charge transfer between the diamond and the fluorofullerene. In contrast to the case of C60F48 acceptors, the presence of a ZnTPP layer prevents the formation of air-induced surface conductivity, showing that the intralayer acts to selectively separate these two doping channels.
Show PACS
73.20.At Surface states, band structure, electron density of states
73.25.+i Surface conductivity and carrier phenomena
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