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29 Aug 2011

Volume 99, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 99, 094101 (2011); http://dx.doi.org/10.1063/1.3629783 (3 pages)

Tomasz Szymborski, Piotr M. Korczyk, Robert Hołyst, and Piotr Garstecki
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A hybrid surface passivation on HgCdTe long wave infrared detector with in-situ CdTe deposition and high-density hydrogen plasma modification

W. D. Hu, X. S. Chen, Z. H. Ye, and W. Lu

Appl. Phys. Lett. 99, 091101 (2011); http://dx.doi.org/10.1063/1.3633103 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2011

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A hybrid surface passivation, in-situ CdTe passivation and high-density hydrogen plasma modification, is used to improve the surface quality of typical n+-on-p HgCdTe long wave infrared photodiode detectors. Three types of surface-passivated pixels, conventional, in-situ CdTe, and hybrid surface passivation, are fabricated in one chip for better comparison. The maximum dynamic resistances of the hybrid-surface-passivation device are increased to 1∼2 times greater than that in the conventional surface passivation technique. Theoretical modeling shows that the hybrid passivation can significantly suppress the trap-assisted tunneling current. Shallow traps close to the Fermi level under reverse voltage, which are the main source of the trap-assisted tunneling current for conventional surface passivation processing, are reduced by the hybrid passivation treatment.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.Dw Photodiodes; phototransistors; photoresistors

A quasi-droplet optofluidic ring resonator laser using a micro-bubble

Wonsuk Lee, Yuze Sun, Hao Li, Karthik Reddy, Misha Sumetsky, and Xudong Fan

Appl. Phys. Lett. 99, 091102 (2011); http://dx.doi.org/10.1063/1.3629814 (3 pages) | Cited 6 times

Online Publication Date: 29 August 2011

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Optofluidic ring resonator lasers based on micro-bubbles filled with liquid gain medium are demonstrated. Due to the sub-micron wall thickness of the micro-bubble, significant amount of the electric field resides inside the liquid. Consequently, micro-bubbles mimic the droplets in air that have 3-dimensional optical confinement, extremely high Q-factors, and versatility in handling liquids of different refractive index. Furthermore, they enable repetitive interrogation and easy directional laser emission out-coupling without evaporation or size/shape variations. The laser using Rhodamine 6G in methanol is achieved with a threshold of 300 nJ/mm2 and 5.3 μJ/mm2 for 1 mM and 10 μM in concentration, respectively.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
47.85.Np Fluidics
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.55.Mv Dye lasers

Doping of GaAs by laser ablated ZnTe

B. Ullrich and G. J. Brown

Appl. Phys. Lett. 99, 091103 (2011); http://dx.doi.org/10.1063/1.3630033 (3 pages)

Online Publication Date: 29 August 2011

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The exposure of GaAs to laser ablated ZnTe causes the formation of donor (Te)-acceptor (Zn) pair states. The photonically transferred dopants resulted in a distinct transition at 1.378 eV (FWHM ≤ 30 meV), visualized by room temperature photocurrent spectroscopy. The presence of impurity absorption in the GaAs was confirmed by transmission measurements. Notably, from the standpoint of technological applications, flipping the applied bias (±1.0 V) to the ZnTe/GaAs heterostructure switches the spectral photocurrent response between the fundamental GaAs absorption and the donor-acceptor transition peak. The results further reveal the influence of the ablating laser line on the optoelectronic device properties.
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61.72.uj III-V and II-VI semiconductors
79.20.Eb Laser ablation
72.40.+w Photoconduction and photovoltaic effects
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.-b Surface treatments

Efficiency droop in InGaN/GaN multiple-quantum-well blue light-emitting diodes grown on free-standing GaN substrate

Zhiqiang Liu, Tongbo Wei, Enqing Guo, Xiaoyan Yi, Liancheng Wang, Junxi Wang, Guohong Wang, Yi Shi, Ian Ferguson, and Jinmin Li

Appl. Phys. Lett. 99, 091104 (2011); http://dx.doi.org/10.1063/1.3605572 (3 pages) | Cited 9 times

Online Publication Date: 29 August 2011

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In this work, the dislocation-related efficiency droop in InGaN/GaN blue light-emitting diodes (LEDs) was investigated by comparing the external quantum efficiency (EQE) of GaN grown on c-plane sapphire and free-standing GaN substrate over a wide range of operation conditions. The values of A, B, and C coefficients had been iteratively obtained by fitting quantum efficiency in the rate equation model. Analysis revealed that threading dislocation density was strongly related to the decrease in EQE of InGaN LEDs at elevated currents by introducing a number of acceptor-like levels with the energy EA lying within the band gap.
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85.60.Jb Light-emitting devices
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Realization of a narrowband single wavelength microring mirror

Amir Arbabi, Young Mo Kang, Ching-Ying Lu, Edmond Chow, and Lynford L. Goddard

Appl. Phys. Lett. 99, 091105 (2011); http://dx.doi.org/10.1063/1.3633111 (3 pages) | Cited 3 times

Online Publication Date: 30 August 2011

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We present a small footprint narrowband on-chip mirror made by integration of a distributed Bragg reflector (DBR) inside a microring resonator. The DBR covers half of the ring’s circumference and is only reflective at one of the ring resonances. Design, fabrication, and characterization of the proposed device are presented. A single reflection peak with maximum power reflectivity of 92.3% and full width at half maximum of 0.4 nm is demonstrated. The device has potential application as an in-line mirror for low-threshold, narrow linewidth single mode laser diodes.
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42.79.Bh Lenses, prisms and mirrors
42.82.Bq Design and performance testing of integrated-optical systems
42.82.Cr Fabrication techniques; lithography, pattern transfer

Random lasing in the composites consisting of photonic crystals and semiconductor nanowires

M. L. Lu, H. Y. Lin, T. T. Chen, and Y. F. Chen

Appl. Phys. Lett. 99, 091106 (2011); http://dx.doi.org/10.1063/1.3631673 (3 pages) | Cited 4 times

Online Publication Date: 30 August 2011

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A well designed material composed of photonic crystals (PCs) and semiconductor nanowires was proposed. To illustrate our working principle, the nanocomposites consisting of SnO2 nanowires and PCs based on Tb(OH)3/SiO2 core/shell nanospheres have been synthesized and characterized. It is found that lasing behavior can be easily achieved using this composite material. The light confined inside the PCs due to the formation of stop band can be extracted along SnO2 nanowires. The observation of random lasing behavior indicates that the composites developed here open a route for the creation of optoelectronic devices.
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42.55.Zz Random lasers
42.60.By Design of specific laser systems

Advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers

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

Appl. Phys. Lett. 99, 091107 (2011); http://dx.doi.org/10.1063/1.3633268 (3 pages) | Cited 10 times

Online Publication Date: 31 August 2011

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The advantages of InGaN light-emitting diodes with GaN-InGaN-GaN barriers are studied. The energy band diagrams, carrier concentrations in the quantum wells, radiative recombination rate in the active region, light-current performance curves, and internal quantum efficiency are investigated. The simulation results show that the InGaN/GaN-InGaN-GaN light-emitting diode has better performance over its conventional InGaN/GaN and InGaN/InGaN counterparts due to the appropriately modified energy band diagrams which are favorable for the injection of electrons and holes and uniform distribution of these carriers in the quantum wells.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.Fg Quantum wells

Patterned polarized fluorescence from a thin film

G. Myhre, A Sayyad, S. Mataka, and S. Pau

Appl. Phys. Lett. 99, 091108 (2011); http://dx.doi.org/10.1063/1.3631670 (3 pages) | Cited 2 times

Online Publication Date: 31 August 2011

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Patterned polarized fluorescence from a thin film comprised of fluorescent dichroic dye dispersed in liquid crystalline polymer is demonstrated with features as small as 11 μm. Cooperative alignment of these fluorescent dichroic molecules in a liquid crystal polymer leads to films exhibiting polarized green, red, and yellow emission. The dichroic fluorescence emission ratios for these films are 10 to 16 depending on the type of the dye. This simple strategy could be utilized for generating large area linearly polarized light sources or electroluminescent displays.
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81.05.Qk Reinforced polymers and polymer-based composites
42.70.Df Liquid crystals
61.30.Vx Polymer liquid crystals
78.55.Bq Liquids
78.66.Qn Polymers; organic compounds

A numerical study of broadband absorbers for visible to infrared detectors

C. A. Keasler and E. Bellotti

Appl. Phys. Lett. 99, 091109 (2011); http://dx.doi.org/10.1063/1.3632110 (3 pages) | Cited 4 times

Online Publication Date: 31 August 2011

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We have studied the electromagnetic response of micro-structured surfaces realized with pillar arrays intended to provide a broadband (0.5–5.0 μm) absorption enhancement for HgCdTe photovoltaic detector arrays. We have considered both square and hexagonal lattice pillar configurations. Using a finite-difference time-domain approach we have found that the absorption enhancement is weakly dependent on the pillar lattice type, but the lattice period does have a significant impact on the enhancement. The use of these micro-structured surfaces makes it possible to eliminate the need for anti-reflection coatings on the detector back-side while maintaining negligible reflectance over a broad spectral band.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Room temperature, continuous-wave coupled-cavity InAsP/InP photonic crystal laser with enhanced far-field emission directionality

Jingqing Huang, Se-Heon Kim, Jonathan Gardner, Philippe Regreny, Christian Seassal, Pablo Aitor Postigo, and Axel Scherer

Appl. Phys. Lett. 99, 091110 (2011); http://dx.doi.org/10.1063/1.3633120 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2011

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We demonstrate room temperature, continuous-wave lasing with enhanced far field emission directionality in coupled-cavity photonic crystal lasers, made with InAsP/InP quantum well material. These surface-emitting lasers can have a very low effective threshold power of 14.6 μW, with a linewidth of 60 pm, and 40% of the surface emitted power concentrated within a small divergence angle of ±30°.
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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
42.70.Qs Photonic bandgap materials

All-optical four-state magnetization reversal in (Ga,Mn)As ferromagnetic semiconductors

M. D. Kapetanakis, P. C. Lingos, C. Piermarocchi, J. Wang, and I. E. Perakis

Appl. Phys. Lett. 99, 091111 (2011); http://dx.doi.org/10.1063/1.3634031 (3 pages) | Cited 2 times

Online Publication Date: 1 September 2011

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Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100 fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after ∼100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un-adiabatic light-induced spin interactions.
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78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Jk Magnetization reversal mechanisms
75.50.Pp Magnetic semiconductors
81.05.Ea III-V semiconductors
78.47.jh Coherent nonlinear optical spectroscopy

Magneto-photonic crystal optical sensors with sensitive covers

Neluka Dissanayake, Miguel Levy, A. Chakravarty, P. A. Heiden, N. Chen, and V. J. Fratello

Appl. Phys. Lett. 99, 091112 (2011); http://dx.doi.org/10.1063/1.3633344 (3 pages) | Cited 1 time

Online Publication Date: 2 September 2011

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We report on a magneto-photonic crystal on-chip optical sensor for specific analyte detection with polypyrrole and gold nano particles as modified photonic crystal waveguide cover layers. The reaction of the active sensor material with various analytes modifies the electronic structure of the sensor layer causing changes in its refractive index and a strong transduction signal. Magneto-photonic crystal enhanced polarization rotation sensitive to the nature of the cover layer detects the index modification upon analyte adsorption. A high degree of selectivity and sensitivity are observed for aqueous ammonia and methanol with polypyrrole and for thiolated-gold- with gold-nanoparticles covers.
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85.70.Sq Magnetooptical devices
42.70.Qs Photonic bandgap materials
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Gn Optical waveguides and couplers
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Dynamics and particle fluxes in atmospheric-pressure electronegative radio frequency microplasmas

K. McKay, D. X. Liu, M. Z. Rong, F. Iza, and M. G. Kong

Appl. Phys. Lett. 99, 091501 (2011); http://dx.doi.org/10.1063/1.3631758 (3 pages) | Cited 4 times

Online Publication Date: 29 August 2011

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We report on intricate dynamics observed in atmospheric-pressure rf electronegative discharges where electrons and anions are separated due to their different mobilities. This results in the formation of positively charged regions between an electronegative plasma core and an oscillating electron ensemble. It is found that for a given input power, the electron, ion (both positive and negative) and neutral fluxes increase as the gap size is reduced, resulting in a more efficient delivery of chemical species to a treated target.
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52.30.-q Plasma dynamics and flow
52.50.Dg Plasma sources
52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties

Laser wakefield acceleration of electron beams beyond 1 GeV from an ablative capillary discharge waveguide

Haiyang Lu, Mingwei Liu, Wentao Wang, Cheng Wang, Jiansheng Liu, Aihua Deng, Jiancai Xu, Changquan Xia, Wentao Li, Hui Zhang, Xiaoming Lu, Cheng Wang, Jianzhou Wang, Xiaoyan Liang, Yuxin Leng, et al.

Appl. Phys. Lett. 99, 091502 (2011); http://dx.doi.org/10.1063/1.3626042 (3 pages) | Cited 6 times

Online Publication Date: 31 August 2011

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Laser wakefield acceleration of electrons well beyond 1 GeV and optical guiding of ultraintense laser pulses of peak powers up to 160 TW over a 4-cm long ablative capillary discharge plasma channel were experimentally demonstrated. Electron beams, with energies up to 1.8 GeV, were generated by using the 130 TW, 55 fs driving laser pulses. A comparison of oxygen-containing acrylic resin (C:O:H = 4:2:7) capillary and no oxygen-containing polyethylene (C:O:H = 1:0:2) capillary measurements suggests that the injection of electron into the laser wakefield is assisted by the ionization of oxygen K-shell electrons.
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52.77.-j Plasma applications
29.20.Ej Linear accelerators
41.75.Fr Electron and positron beams
41.75.Jv Laser-driven acceleration
52.38.Hb Self-focussing, channeling, and filamentation in plasmas

Photoluminescence of hydrogen amorphous carbon nitrile particles obtained in a 13.56 MHz dusty plasma

I. Géraud-Grenier, R. Jaffiol, V. Massereau-Guilbaud, and A. Plain

Appl. Phys. Lett. 99, 091503 (2011); http://dx.doi.org/10.1063/1.3632112 (3 pages) | Cited 2 times

Online Publication Date: 1 September 2011

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In this article, we report the photoluminescence (PL) of small particles generated in CH4/N2 radiofrequency (13.56 MHz) discharges. The particles have been produced with various mixtures of N2 and CH4 gases. The particle PL has been analysed using fluorescence microscopy in air with an Ar+ laser at 488 nm. It appears that the photoluminescence intensity is in relation to the particle size. However, the incorporation of nitrogen modifies the peak position of the PL spectrum.
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78.55.Qr Amorphous materials; glasses and other disordered solids
52.77.-j Plasma applications
78.55.Hx Other solid inorganic materials

Generation of laser-induced plasma in supercritical water and vibrational spectroscopic study of accompanying stimulated Raman scattering

Hiroharu Yui, Takaaki Tomai, Masayoshi Sawada, and Kazuo Terashima

Appl. Phys. Lett. 99, 091504 (2011); http://dx.doi.org/10.1063/1.3627161 (3 pages)

Online Publication Date: 2 September 2011

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We have formed a laser-induced plasma (LIP) in supercritical water (SCW) and studied associated molecular vibrations using spectroscopic methods. The accompanying forward and backward stimulated Raman scattering (SRS) of water molecules showed anisotropic behavior at supercritical conditions (>647 K and >22.1 MPa). The Raman shift of the backward SRS indicated that attractive interactions between water molecules and excess electrons generated by the LIP were dominant in the SCW. The backward SRS spectrum provided a microscopic view of the hydration environment around an excess electron, which is useful for controlling electron-driven chemical reactions and materials processing in SCW.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Bv Rayleigh scattering; stimulated Brillouin and Raman scattering
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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Dense and uniform Au nanospheres on glass through confined nanosecond pulsed laser irradiation

Yingling Yang, Martin Y. Zhang, and Gary J. Cheng

Appl. Phys. Lett. 99, 091901 (2011); http://dx.doi.org/10.1063/1.3633123 (3 pages) | Cited 1 time

Online Publication Date: 29 August 2011

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We utilize confined nanosecond pulsed laser irradiation to fabricate one monolayer of gold nanospheres on glass, with narrow size distribution and high packing densities. With a laser fluence of ∼400 mJ/cm2, the size of the nanospheres is as small as ∼50 nm and the packing density is as high as ∼2 × 1010 cm−2. The light heating efficiency is higher for smaller size nanospheres, so the heating and sphere regrowing process naturally results in the narrow size distribution for the gold nanospheres.
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81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

First-principles generalized gradient approximation + U study of cubic CuAl2O4

Qi-Jun Liu and Zheng-Tang Liu

Appl. Phys. Lett. 99, 091902 (2011); http://dx.doi.org/10.1063/1.3630131 (3 pages)

Online Publication Date: 29 August 2011

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We have investigated the electronic, magnetic, mechanical, and optical properties in cubic CuAl2O4 by a first-principles ultrasoft pseudopotential of the plane-wave within the density-functional theory (DFT) plus the generalized gradient approximation (GGA) + U (Hubbard parameter) formalism. We find the polarized hole dz2 character induced the dz2 magnetic orbital ordering and the p-d hybridization results in the covalent bonding between Cu and O. The origins of electrons transitions in dielectric function are consistent with electronic structure aroused by crystal-field and Janhn-Teller effect.
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71.20.Ps Other inorganic compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.10.Dg Crystal-field theory and spin Hamiltonians
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Improving thermal stability of hard coating films via a concept of multicomponent alloying

H. Lind, R. Forsén, B. Alling, N. Ghafoor, F. Tasnádi, M. P. Johansson, I. A. Abrikosov, and M. Odén

Appl. Phys. Lett. 99, 091903 (2011); http://dx.doi.org/10.1063/1.3631672 (3 pages) | Cited 13 times

Online Publication Date: 29 August 2011

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We propose a design route for the next generation of nitride alloys via a concept of multicomponent alloying based on self-organization on the nanoscale via a formation of metastable intermediate products during the spinodal decomposition. We predict theoretically and demonstrate experimentally that quasi-ternary (TiCrAl)N alloys decompose spinodally into (TiCr)N and (CrAl)N-rich nanometer sized regions. The spinodal decomposition results in age hardening, while the presence of Cr within the AlN phase delays the formation of a detrimental wurtzite phase leading to a substantial improvement of thermal stability compared to the quasi-binary (TiAl)N or (CrAl)N alloys.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.30.Mh Solid-phase precipitation
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
65.40.-b Thermal properties of crystalline solids
68.35.Gy Mechanical properties; surface strains

Growth of Si-doped GaInP on Ge-on-Si substrates and its photoluminescence characteristics

Changjae Yang, Sangsoo Lee, Keun Wook Shin, Sewoung Oh, Jinsub Park, Chang-Zoo Kim, Won-Kyu Park, Seung-kyu Ha, Won Jun Choi, and Euijoon Yoon

Appl. Phys. Lett. 99, 091904 (2011); http://dx.doi.org/10.1063/1.3623757 (3 pages) | Cited 5 times

Online Publication Date: 30 August 2011

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Optical properties of Si-doped GaInP grown on Ge-on-Si substrates were investigated using photoluminescence (PL). Similar to spontaneously ordered GaInP, two peaks were observed around 1.74 and 1.85 eV at 19 K; however, no satellite peaks were observed in the selected-area diffraction pattern. Based on temperature-dependent PL, the peak at 1.74 eV was attributed to the donor–acceptor pair transition caused by the amphoteric characteristics of Si and/or Ge from the dopant and/or substrate. In addition, the S-shape in the temperature dependence of the 1.85 eV peak was attributed to the interaction of the donor levels with the conduction band of GaInP.
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68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Tuning thermal transport in nanotubes with topological defects

Jian Wang, Liang Li, and Jian-Sheng Wang

Appl. Phys. Lett. 99, 091905 (2011); http://dx.doi.org/10.1063/1.3631725 (3 pages) | Cited 3 times

Online Publication Date: 30 August 2011

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Using the atomistic nonequilibrium Green’s function, we find that thermal conductance of carbon nanotubes with presence of topological lattice imperfects is remarkably reduced, due to the strong Rayleigh scattering of high-frequency phonons. Phonon transmission across multiple defects behaves as a cascade scattering based with the random phase approximation. We elucidate that phonon scattering by structural defects is related to the spatial fluctuations of local vibrational density of states (LVDOS). An effective method of tuning thermal transport in low-dimensional systems through the modulation of LVDOS has been proposed. Our findings provide insights into experimentally controlling thermal transport in nanoscale devices.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
02.30.-f Function theory, analysis
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion
61.72.-y Defects and impurities in crystals; microstructure
63.20.-e Phonons in crystal lattices
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Zero-phonon emission and magnetic polaron parameters in EuTe

A. B. Henriques, G. D. Galgano, E. Abramof, B. Diaz, and P. H. O. Rappl

Appl. Phys. Lett. 99, 091906 (2011); http://dx.doi.org/10.1063/1.3634030 (3 pages) | Cited 1 time

Online Publication Date: 31 August 2011

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A phonon structure in the photoluminescence of EuTe was discovered, with a well-defined zero-phonon emission line (ZPL). The ZPL redshifts linearly with the intensity of applied magnetic field, indicating spin relaxation of the photoexcited electron, and saturates at a lower magnetic field than the optical absorption bandgap, which is attributed to formation of magnetic polarons. From the difference in these saturation fields, the zero-field polaron binding energy and radius are estimated to be 43 meV and 3.2 (in units of the EuTe lattice parameter), respectively.
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78.20.-e Optical properties of bulk materials and thin films
78.55.-m Photoluminescence, properties and materials
78.20.Ls Magneto-optical effects
71.20.Nr Semiconductor compounds
71.38.-k Polarons and electron-phonon interactions

Graphitization of amorphous carbon on a multiwall carbon nanotube surface by catalyst-free heating

Koji Asaka, Motoyuki Karita, and Yahachi Saito

Appl. Phys. Lett. 99, 091907 (2011); http://dx.doi.org/10.1063/1.3630132 (3 pages) | Cited 5 times

Online Publication Date: 1 September 2011

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Structural changes in amorphous carbon coating the surfaces of multiwall carbon nanotubes (MWNTs) under applying an electric current were investigated by in situ transmission electron microscopy with simultaneous measurements of the bias voltage and electric current. Joule heating transformed amorphous carbon on the surfaces of individual MWNTs suspended between gold electrodes into graphite layers even without a metal catalyst through a phase of glasslike carbon. The MWNTs after the formation of ordered surface layers sustained a high current with a density of up to 3.1 × 108 A/cm2.
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81.16.-c Methods of micro- and nanofabrication and processing
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Gh Other heat and thermomechanical treatments
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.De Nanotubes

Effect of compressive stress on stability of N-doped p-type ZnO

Xingyou Chen, Zhenzhong Zhang, Bin Yao, Mingming Jiang, Shuangpeng Wang, Binghui Li, Chongxin Shan, Lei Liu, Dongxu Zhao, and Dezhen Shen

Appl. Phys. Lett. 99, 091908 (2011); http://dx.doi.org/10.1063/1.3631677 (3 pages) | Cited 4 times

Online Publication Date: 1 September 2011

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Nitrogen-doped p-type zinc oxide (p-ZnO:N) thin films were fabricated on a-/c-plane sapphire (a-/c-Al2O3) by plasma-assisted molecular beam epitaxy. Hall-effect measurements show that the p-type ZnO:N on c-Al2O3 degenerated into n-type after a preservation time; however, the one grown on a-Al2O3 showed good stability. The conversion of conductivity in the one grown on c-Al2O3 ascribed to the faster disappearance of NO and the growing N2(O), which is demonstrated by x-ray photoelectron spectroscopy (XPS). Compressive stress, caused by lattice misfit, was revealed by Raman spectra and optical absorption spectra, and it was regarded as the root of the instability in ZnO:N.
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73.61.Ga II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
72.20.My Galvanomagnetic and other magnetotransport effects

Donor bound excitons involving a hole from the B valence band in ZnO: Time resolved and magneto-photoluminescence studies

S. L. Chen, W. M. Chen, and I. A. Buyanova

Appl. Phys. Lett. 99, 091909 (2011); http://dx.doi.org/10.1063/1.3628332 (3 pages) | Cited 3 times

Online Publication Date: 1 September 2011

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Show Abstract
Time-resolved and magneto-photoluminescence (PL) studies are performed for the so-called I6B and I7B excitonic transitions, previously attributed to neutral donor bound excitons involving a hole from the B valence band (VB), D0XB. It is shown that PL decays of these emissions at 2 K are faster than that of their I6 and I7 counterparts involving an A VB hole, which is interpreted as being due to energy relaxation of the hole assisted by acoustic phonons. From the magneto-PL measurements, values of effective Landé g factors for conduction electrons and B VB holes are determined as ge = 1.91, gh// = 1.79, and gh⊥ = 0, respectively.
Show PACS
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
71.55.Gs II-VI semiconductors
78.47.jd Time resolved luminescence
78.20.Ls Magneto-optical effects
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