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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Direct modulation of excited state quantum dot lasers

B. J. Stevens, D. T. D. Childs, H. Shahid, and R. A. Hogg

Appl. Phys. Lett. 95, 061101 (2009); http://dx.doi.org/10.1063/1.3193664 (3 pages) | Cited 8 times

Online Publication Date: 10 August 2009

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The use of the excited state quantum dot lasers for high speed direct modulation is proposed and demonstrated. A direct comparison of lasers utilizing the ground state and excited state from the same laser material reveals a factor of two increase in the K-factor limited bandwidth. This is attributed to an increase in the saturated gain and reduced carrier scattering time of the excited state compared to the ground state.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking

Complex emission dynamics of type-II GaSb/GaAs quantum dots

Kamil Gradkowski, Nicola Pavarelli, Tomasz J. Ochalski, David P. Williams, Jun Tatebayashi, Guillaume Huyet, Eoin P. O’Reilly, and Diana L. Huffaker

Appl. Phys. Lett. 95, 061102 (2009); http://dx.doi.org/10.1063/1.3202419 (3 pages) | Cited 7 times

Online Publication Date: 10 August 2009

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Optical properties of the GaSb/GaAs quantum dot system are investigated using a time-resolved photoluminescence technique. In this type-II heterostructure the carriers of different species are spatially separated and, as a consequence, a smooth evolution of both the emission wavelength and decay timescale is observed. A wavelength shift of 170 nm is measured simultaneously with the progressive timescale change from 100 ps to 23 ns. These phenomena are explained by the evolution of the carrier density, which brings a modification to the optical transition probability as well as the shift in the emission toward the higher energies.
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78.67.Hc Quantum dots
78.47.jd Time resolved luminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)

External cavity quantum cascade laser tunable from 7.6 to 11.4 μm

Andreas Hugi, Romain Terazzi, Yargo Bonetti, Andreas Wittmann, Milan Fischer, Mattias Beck, Jérôme Faist, and Emilio Gini

Appl. Phys. Lett. 95, 061103 (2009); http://dx.doi.org/10.1063/1.3193539 (3 pages) | Cited 41 times

Online Publication Date: 11 August 2009

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We present the development of a broad gain quantum cascade active region. By appropriate cascade design and using a symmetric active region arrangement, we engineer a flat gain and increase the total modal gain in the desired spectral range. Grating-coupled external cavity quantum cascade lasers using this symmetric active region are tunable from 7.6 to 11.4 μm with a peak optical output power of 1 W and an average output power of 15 mW at room-temperature. With a tuning of over 432 cm−1, this single source covers an emission range of over 39% around the center frequency.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Dj Gratings
42.60.Fc Modulation, tuning, and mode locking
42.60.By Design of specific laser systems

Growths of staggered InGaN quantum wells light-emitting diodes emitting at 520–525 nm employing graded growth-temperature profile

Hongping Zhao, Guangyu Liu, Xiao-Hang Li, G. S. Huang, Jonathan D. Poplawsky, S. Tafon Penn, Volkmar Dierolf, and Nelson Tansu

Appl. Phys. Lett. 95, 061104 (2009); http://dx.doi.org/10.1063/1.3204446 (3 pages) | Cited 51 times

Online Publication Date: 12 August 2009

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Three-layer staggered InGaN quantum wells (QWs) light-emitting diodes (LEDs) emitting at 520–525 nm were grown by metal-organic chemical vapor deposition by employing graded growth-temperature profile. The use of staggered InGaN QW, with improved electron-hole wave functions overlap design, leads to an enhancement of its radiative recombination rate. Both cathodoluminescence and electroluminescence measurements of three-layer staggered InGaN QW LED exhibited enhancements by 1.8–2.8 and 2.0–3.5 times, respectively, over those of conventional InGaN QW LED.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Hk Cathodoluminescence, ionoluminescence
78.60.Fi Electroluminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Photonic crystal membrane waveguides with low insertion losses

Quynh Vy Tran, Sylvain Combrié, Pierre Colman, and Alfredo De Rossi

Appl. Phys. Lett. 95, 061105 (2009); http://dx.doi.org/10.1063/1.3205452 (3 pages) | Cited 20 times

Online Publication Date: 13 August 2009

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We demonstrate experimentally that the fiber to fiber total insertion loss into a single-mode waveguide in a suspended photonic crystal membrane can be reduced to less than 10 dB (input, output, and propagation) without introducing any supplementary processing step (e.g., polymer deposition and etching). This is achieved through a suitable design of the waveguide end-facets minimizing the impedance mismatch and thereby the residual reflectance at the waveguide ends.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

Probing exciton-phonon interaction in AlN epilayers by photoluminescence

A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 95, 061106 (2009); http://dx.doi.org/10.1063/1.3206672 (3 pages) | Cited 4 times

Online Publication Date: 14 August 2009

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Deep ultraviolet (DUV) photoluminescence (PL) spectroscopy has been employed to investigate the exciton-phonon interaction in AlN. Longitudinal optical (LO) phonon replicas of free exciton recombination lines were observed in PL emission spectra, revealing the coupling of excitons with LO phonons. We have quantified such interaction by measuring Huang–Rhys factor based on polarization resolved DUV PL measurements. It was observed that the exciton-phonon coupling strength in AlN depends on the polarization configuration and is much larger in the direction with the electrical field (math) of the emitted light perpendicular to the wurtzite c-axis (math⊥math) than in the direction of math∥math. Furthermore, a larger coupling constant was also measured in AlN than in GaN. The large effective hole to electron mass ratio in AlN, especially in the math⊥math configuration, mainly accounts for the observed results.
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63.20.kk Phonon interactions with other quasiparticles
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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Experimental investigation of transition from Fowler–Nordheim field emission to space-charge-limited flows in a nanogap

Sudeep Bhattacharjee and Tathagata Chowdhury

Appl. Phys. Lett. 95, 061501 (2009); http://dx.doi.org/10.1063/1.3194297 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2009

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An experimental investigation of the transition from Fowler–Nordheim (FN) field emission to space-charge-limited (SCL) flows in a nanogap is presented. Electrodes with gap size D ∼ 30–70 nm corresponding to D/λo up to a maximum of ∼ 2×103, where λo is the de Broglie wavelength of the space-charge-electrons, are experimented. The transition from the FN field emission to the classical SCL flow is a function of the applied bias and lies in the range 5–15 V. The equilibrium transmitted current density for the 50 nm sample indicates a transition from the FN to the quantum SCL flow at ∼ 0.4 V with D/λo of ∼ 35 and then gradually to the classical SCL behavior as the voltage is increased beyond ∼ 9 V. The experiments indicate no sharp demarcation between the different regimes.
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73.63.Rt Nanoscale contacts
72.20.Ht High-field and nonlinear effects
82.45.Fk Electrodes

Properties of dielectric-barrier-free atmospheric pressure microplasma driven by submicrosecond dc pulse voltage

Chang-Seung Ha (하창승), Joon-Young Choi (최준영), Dong-Hyun Kim (김동현), Chung-Hoo Park (박정후), Hae June Lee (이해준), and Ho-Jun Lee (이호준)

Appl. Phys. Lett. 95, 061502 (2009); http://dx.doi.org/10.1063/1.3194298 (3 pages) | Cited 7 times

Online Publication Date: 10 August 2009

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Atmospheric pressure microplasma driven by dc pulse is developed. This device has a simple structure comprised of a flowing helium (He) feed gas and dielectric-free metal electrodes without an external current limiting resistor. It is shown that a stable glow mode plasma can be sustained without arc runaway by limiting the voltage pulse width to shorter than 300 ns. The properties of the device are reported in terms of discharge current waveforms, rotational temperature of N2+, and spatiotemporally resolved optical emission characteristics.
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52.75.-d Plasma devices
52.80.Hc Glow; corona
52.25.Mq Dielectric properties
52.50.Dg Plasma sources

Impact energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation

Qiu Yuan Lu, Liu He Li, Jian Hui Li, Ricky K. Y. Fu, and Paul K. Chu

Appl. Phys. Lett. 95, 061503 (2009); http://dx.doi.org/10.1063/1.3204697 (3 pages) | Cited 3 times

Online Publication Date: 12 August 2009

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The implantation energy and retained dose uniformity in enhanced glow discharge plasma immersion ion implantation (EGD-PIII) is investigated numerically and experimentally. Depth profiles obtained from different samples processed by EGD-PIII and traditional PIII are compared. The retained doses under different pulse widths are calculated by integrating the area under the depth profiles. Our results indicate that the improvement in the impact energy and retained dose uniformity by this technique is remarkable.
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52.77.Dq Plasma-based ion implantation and deposition
61.72.U- Doping and impurity implantation
52.80.Hc Glow; corona
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Speed determination of single Sr adatoms moving within Si(111)-7×7 half unit cells

R. Zhachuk, S. Teys, B. Olshanetsky, and S. Pereira

Appl. Phys. Lett. 95, 061901 (2009); http://dx.doi.org/10.1063/1.3198205 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2009

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In this paper we report on the motion of individual Sr adatoms within the limits of Si(111)-7×7 half unit cells (HUCs). The fast movement of the atom at the Si surface produces sharp signal fluctuations in scanning tunneling microscopy (STM) images resulting into noiselike patches. It is found that the length of the observed image streaks is a function of the scanning tip velocity. A Monte Carlo simulation implementing a model of independently moving Sr adatom and scanning tip, accounts for the observed STM image features quantitatively. Thus, by colleting STM images at various scanning speeds and matching simulated image features to the experimental observations, allows the average speed of Sr adatom within the limits of Si(111)-7×7 HUC to be estimated: 300 nm/s.
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68.35.Fx Diffusion; interface formation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Quasi-single-crystal (001) SrTiO3 templates on Si

J. W. Park, S. H. Baek, C. W. Bark, M. D. Biegalski, and C. B. Eom

Appl. Phys. Lett. 95, 061902 (2009); http://dx.doi.org/10.1063/1.3202398 (3 pages) | Cited 5 times

Online Publication Date: 10 August 2009

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The integration of multifunctional oxides on semiconductor devices requires the formation of single-crystal-like oxide templates directly on silicon. We report the fabrication of quasi-single-crystal (001) SrTiO3 templates on (001) Si by annealing 100 nm thick molecular beam epitaxy-grown epitaxial SrTiO3 films at 900 °C. The full width at half maximum of the (002) rocking curve is 0.006°, which is much narrower than SrTiO3 bulk single crystals. An atomically smooth TiO2-terminated surface is obtained by buffered-HF etching, which allows us to create functional oxide heterointerfaces on Si. Epitaxial SrRuO3 thin films grown on the quasi-single-crystal SrTiO3 template exhibit a superior crystalline quality and surface morphology.
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68.55.J- Morphology of films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Thermoelastic damping in micromechanical resonators

Thomas H. Metcalf, Bradford B. Pate, Douglas M. Photiadis, and Brian H. Houston

Appl. Phys. Lett. 95, 061903 (2009); http://dx.doi.org/10.1063/1.3190509 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2009

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We show that the dominant energy loss mechanism in plate modes of a 1.5 μm thick silicon micromechanical resonator is thermoelastic damping. In situ ultra-high vacuum annealing lowers the dissipation of two neighboring resonance modes (460 and 510 kHz) at 120 K to Q−1 ≤ 5×10−7. From 120 to 400 K, the Q−1 of these modes increase at different rates, in quantitative agreement with a modification (that accounts for mode shape) of Zener’s theory of thermoelastic damping.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
61.72.Cc Kinetics of defect formation and annealing
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

A multiscale approach to diffraction tomography of complex three-dimensional objects

F. Simonetti, L. Huang, and N. Duric

Appl. Phys. Lett. 95, 061904 (2009); http://dx.doi.org/10.1063/1.3204021 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2009

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Tomography of complex three-dimensional objects with diffractive waves remains an open challenge due to the large number of scattering measurements required to obtain a stable solution to the inverse problem of reconstructing an image of the object from a set of independent scattering experiments. Here, this problem is addressed with a multiscale approach that is demonstrated experimentally using ultrasonic waves and which leads to high resolution images comparable to x-ray computerized tomography but without the limitations associated with ionizing radiation.
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42.30.Wb Image reconstruction; tomography
42.25.Fx Diffraction and scattering
87.63.L- Visual imaging

Polarization and temperature dependence of photoluminescence of m-plane GaN grown on γ-LiAlO2 (100) substrate

B. Liu, J. Y. Kong, R. Zhang, Z. L. Xie, D. Y. Fu, X. Q. Xiu, P. Chen, H. Lu, P. Han, Y. D. Zheng, and S. M. Zhou

Appl. Phys. Lett. 95, 061905 (2009); http://dx.doi.org/10.1063/1.3204453 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2009

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We investigated the polarization and temperature dependence of photoluminescence (PL) of m-plane GaN grown on γ-LiAlO2 (100) substrate. The calculated electronic band structure with k•p Hamiltonian points out the energy splitting as well as polarization selection originate from the m-plane GaN epilayer under anisotropic strain. The polarization-angle dependence PL spectra are found to be selected from in-plane x- and z-polarized emission, corresponding to T1 and T2 transition. And the intensity distribution of the fitting peaks satisfies the Malus’ law. An S-shape energy evolution of near band edge peak on temperatures is observed, which originates from the transition between the localized holes and electrons in triangular potentials induced by basal stacking faults.
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78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Probing the structural, crystalline, and electrical properties of carbon nanotubes grown on nickel filled carbon nanofibers

Hongxin Zhang, Peter X. Feng, Peng Jin, Vladimir I. Makarov, Luis Fonseca, Gerardo Morell, and Brad R. Weiner

Appl. Phys. Lett. 95, 061906 (2009); http://dx.doi.org/10.1063/1.3204475 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2009

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Carbon nanotubes (CNTs) were produced on nickel filled carbon nanofiber substrates. The carbon source was provided by irradiation of pyrolytic graphite. The mean outer diameter of the CNTs, which was identified as multiwalled carbon nanotubes, varies in the range of 5–15 nm. The crystallographic structures, chemical compositions, and bond structures of the carbon materials were investigated. The modified crystal structure was attributed to better lattice arrangement resulting from increased lattice vibration at high substrate temperature. The improved electron field emission behavior of the obtained sample at higher temperature could be caused by the increasing effective emission sites.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption

Influence of deviatoric stress on the pressure-induced structural phase transition of ZnO studied by optical second harmonic generation measurements

L. Bayarjargal, B. Winkler, E. Haussühl, and R. Boehler

Appl. Phys. Lett. 95, 061907 (2009); http://dx.doi.org/10.1063/1.3205120 (3 pages) | Cited 5 times

Online Publication Date: 12 August 2009

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The pressure-induced B4⇆B1 structural phase transition of ZnO has been studied with the second harmonic generation (SHG) technique. Measurements in nonhydrostatic and hydrostatic pressure transmitting media show slightly different transition pressures (9–11 GPa) and a different pressure dependence of the SHG intensities. These observations are consistent with the presence of a tetragonal and hexagonal intermediate phase as a result of hydrostatic and axial compression, respectively. In contrast to earlier work, it is shown that it is not necessary to use nanocrystalline starting material to be able to recover the B1 phase at ambient conditions.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Characteristics of ultraviolet photoluminescence from high quality tin oxide nanowires

Rui Chen, G. Z. Xing, J. Gao, Z. Zhang, T. Wu, and H. D. Sun

Appl. Phys. Lett. 95, 061908 (2009); http://dx.doi.org/10.1063/1.3205122 (3 pages) | Cited 16 times

Online Publication Date: 12 August 2009

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We investigate the optical properties of ultraviolet range emission from high quality tin oxide nanowires prepared by vapor-liquid-solid growth technique. Temperature dependent photoluminescence (PL) measurement is performed between 10 and 300 K. At low temperatures, the PL originates from radiative recombination of excitons bound to neutral donors, donor-acceptor pair transition and their associated longitudinal optical (LO) phonon replicas. The LO-phonon replicas up to third order with Huang–Rhys factor of 0.34 are observed. Evolution of the peaks and the origin of PL thermal quenching at high temperatures are discussed in detail.
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81.07.Vb Quantum wires
78.67.Lt Quantum wires
78.55.Hx Other solid inorganic materials
78.40.Fy Semiconductors
73.21.Hb Quantum wires
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.-y Excitons and related phenomena

Optoacoustic response of a single submicronic gold particle revealed by the picosecond ultrasonics technique

Yannick Guillet, Clément Rossignol, Bertrand Audoin, Gaëtan Calbris, and Serge Ravaine

Appl. Phys. Lett. 95, 061909 (2009); http://dx.doi.org/10.1063/1.3205472 (3 pages) | Cited 7 times

Online Publication Date: 13 August 2009

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The optoacoustic response of a single submicron (430 nm) gold particle embedded in a silica thin film is experimentally revealed by femtosecond pump-probe experiments. A semianalytical model is developed to calculate the transient reflectivity accounting for optical index changes in both media and for particle and film surface displacements. The displacement of the particle-film interface turns out to be the major contribution to the measured signal. The amplitude of the acoustical component of the transient reflectivity is modulated by the depth at which the particle is buried in the film.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
62.65.+k Acoustical properties of solids
78.47.J- Ultrafast spectroscopy (<1 psec)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Strong photoluminescence at 1.53 μm from GaSb/AlGaSb multiple quantum wells grown on Si substrate

D. H. Nguyen, J. Park, Y. K. Noh, M. D. Kim, D. Lee, and J. E. Oh

Appl. Phys. Lett. 95, 061910 (2009); http://dx.doi.org/10.1063/1.3205473 (3 pages) | Cited 1 time

Online Publication Date: 13 August 2009

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Strong photoluminescence at 1.53 μm was obtained from a GaSb/Al0.4Ga0.6Sb multiple-quantum-well sample grown on Si substrate, indicating greatly reduced defects by InSb quantum-dot layers that terminate dislocations. The carrier lifetime of 1.4 ns, comparable to typical InP-based quantum wells, and its independence on excitation power indicates the low defect density. Due to the wide well width and tensile strain, photoluminescence was dominated by the light hole-electron transition at low temperature. However, the heavy hole-electron transition was dominant at room temperature due to the proximity of energy levels and higher density of states for the heavy hole transition.
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78.67.De Quantum wells
73.21.Fg Quantum wells
61.72.Lk Linear defects: dislocations, disclinations
73.20.At Surface states, band structure, electron density of states
78.55.Cr III-V semiconductors

Photovoltaic cells fabricated utilizing core-shell CdSe/ZnSe quantum dot/multiwalled carbon nanotube heterostructures

Fushan Li, Dong Ick Son, Tae Whan Kim, Euidock Ryu, Sang Wook Kim, Sun Kyun Lee, and Yong Hoon Cho

Appl. Phys. Lett. 95, 061911 (2009); http://dx.doi.org/10.1063/1.3204696 (3 pages) | Cited 11 times

Online Publication Date: 13 August 2009

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An efficient quenching of the photoluminescence spectrum was observed for the quantum dot (QD)-multiwalled carbon nanotubes (MWCNTs) nanocomposite. While the lifetime of the blue emission from ZnSe shell was significantly reduced, it did not exhibit any obvious change in the red emission from CdSe core-crystal. This difference revealed two competing charge transfer processes between the CdSe core-crystal, the ZnSe shell and the MWCNTs. Current-voltage measurements on devices fabricated utilizing CdSe QD-MWCNT nanocomposites showed photovoltaic (PV) effect under ultraviolet light illumination. Charge transfer mechanisms of the PV cells are described on the basis of the experimental results.
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85.60.-q Optoelectronic devices
85.35.-p Nanoelectronic devices
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Electrical transport in laser-crystallized polycrystalline silicon-germanium thin-films

L.-P. Scheller, M. Weizman, N. H. Nickel, and B. Yan

Appl. Phys. Lett. 95, 062101 (2009); http://dx.doi.org/10.1063/1.3194147 (3 pages) | Cited 6 times

Online Publication Date: 10 August 2009

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We report on the electrical transport properties of intentionally undoped, laser-crystallized polycrystalline silicon-germanium thin-films. The electrical transport in this material strongly depends on the alloy composition and the crystallization procedure. At low temperatures the undoped germanium-rich samples show an unexpected high p-type conductivity with a weak temperature dependence. Posthydrogenation results in a pronounced decrease in the conductivity and a change in the dominating low temperature transport behavior. The results are discussed in terms of a grain-boundary dominated transport model.
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73.61.Le Other inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries

Characterization of boron charge traps at the interface of Si/SiO2 using second harmonic generation

H. Park, J. Qi, Y. Xu, K. Varga, S. M. Weiss, B. R. Rogers, G. Lüpke, and N. Tolk

Appl. Phys. Lett. 95, 062102 (2009); http://dx.doi.org/10.1063/1.3202420 (3 pages) | Cited 10 times

Online Publication Date: 10 August 2009

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We report results from optical second harmonic generation studies of boron charge traps near the interface of Si/SiO2. Our data suggest that a static electric field at the interface is formed during the oxide growth process due to the presence of negative boron ions (B−) in the silicon substrate and positive boron ions (B+) in the oxide. We demonstrated that the B+ state traps could be filled through the creation of neutral boron states created by internal photoelectron emission. By fitting our data, we found that the effective interface susceptibility |χ(2)| depends on doping concentration.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.uf Ge and Si
79.60.Jv Interfaces; heterostructures; nanostructures

Stress-induced anomalous shift of optical band gap in ZnO:Al thin films

Bhaskar Chandra Mohanty, Yeon Hwa Jo, Deuk Ho Yeon, Ik Jin Choi, and Yong Soo Cho

Appl. Phys. Lett. 95, 062103 (2009); http://dx.doi.org/10.1063/1.3202399 (3 pages) | Cited 24 times

Online Publication Date: 11 August 2009

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Thickness-dependent stress relaxation and its unreported effect on optical band gap of Al-doped ZnO thin films have been investigated. The thinnest film ( ∼ 84 nm) had a stress of −8.39×109 Nm−2, carrier concentration of 1.73×1019 cm−3 and optical band gap of 3.69 eV, a value significantly higher than the reported ones. With increase in thickness, magnitude of the stress decreased, and correspondingly a redshift of fundamental absorption band edge was observed. A linear dependence of optical band gap on stress in the films with a coefficient of 54.6 meV/GPa has been observed.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
73.61.Ga II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.jd Thickness
81.05.Dz II-VI semiconductors

Defect reduction in epitaxial GaSb grown on nanopatterned GaAs substrates using full wafer block copolymer lithography

Smita Jha, C.-C. Liu, T. S. Kuan, S. E. Babcock, P. F. Nealey, J. H. Park, L. J. Mawst, and T. F. Kuech

Appl. Phys. Lett. 95, 062104 (2009); http://dx.doi.org/10.1063/1.3204013 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2009

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Defect reduction in the large lattice mismatched system of GaSb on GaAs, ∼ 7%, was accomplished using full wafer block copolymer (BCP) lithography. A self-assembled BCP mask layer was used to generate a hexagonal pattern of ∼ 20 nm holes on ∼ 40 nm centers in a 20 nm SiO2 layer. GaSb growth initially takes place selectively within these holes leading to a dense array of small, strain-relaxed epitaxial GaSb islands. The GaSb grown on the patterned SiO2 layer exhibits a reduction in the x-ray linewidth attributed to a decrease in the threading dislocation density when compared to blanket pseudomorphic film growth.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
52.77.Dq Plasma-based ion implantation and deposition
68.55.ag Semiconductors

Controllable resistance switching behavior of NiO/SiO2 double layers for nonvolatile memory applications

Ji-Hyuk Choi, Sachindra Nath Das, and Jae-Min Myoung

Appl. Phys. Lett. 95, 062105 (2009); http://dx.doi.org/10.1063/1.3204450 (3 pages) | Cited 7 times

Online Publication Date: 12 August 2009

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Resistive switching characteristics of the double layer (NiO/SiO2) were studied for possible nonvolatile memory applications. The effect of SiO2 thickness variation in the memory device was investigated. A repeatable resistance switching behavior was observed with on/off ratio 105. The operation voltage of the device depended on the thickness of SiO2 layer and it increases with increasing SiO2 thickness. High-resolution transmission electron microscopy analyses revealed that the formation/rapture of Ni filament like percolation path inside SiO2 layer is responsible for the current transport mechanism.
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73.61.-r Electrical properties of specific thin films
84.30.Sk Pulse and digital circuits
68.55.-a Thin film structure and morphology
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