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17 Nov 2008

Volume 93, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 93, 201101 (2008); http://dx.doi.org/10.1063/1.3025818 (3 pages)

W. Dai and C. M. Soukoulis
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Converging and wave guiding of Gaussian beam by two-layer dielectric rods

W. Dai and C. M. Soukoulis

Appl. Phys. Lett. 93, 201101 (2008); http://dx.doi.org/10.1063/1.3025818 (3 pages) | Cited 2 times

Online Publication Date: 17 November 2008

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We have shown that a two-layer dielectric structure can give excellent beaming and enhanced transmission simultaneously of a Gaussian source. The front surface of the layer of dielectric rods supports surface states and the rear grading layer couples the surface states to radiation modes. By repeating periodically this two-layer structure, one can obtain excellent beaming and enhanced transmission for very long distances.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Gn Optical waveguides and couplers

Compensation of thermal refraction effect in high-Q toroidal microresonator by polydimethylsiloxane coating

L. He, Y.-F. Xiao, C. Dong, J. Zhu, V. Gaddam, and L. Yang

Appl. Phys. Lett. 93, 201102 (2008); http://dx.doi.org/10.1063/1.3030986 (3 pages) | Cited 26 times

Online Publication Date: 17 November 2008

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We experimentally and theoretically characterize the thermal refraction effect in a silica microtoroid and demonstrate that such effect can be reduced or even eliminated by applying a thin layer of polydimethylsiloxane (PDMS) to the surface of the silica resonator. By increasing the coating thickness, the whispering gallery modes (WGMs) experience a transition from redshift to blueshift induced by thermal absorption. Experiment results demonstrate that at the thickness of 0.52 μm, the fundamental WGM with observed Q factor of 1.5×106 shows no shift with the input optical power since the thermal refraction of the silica for this mode is compensated completely by the PDMS layer, which has an opposite thermal refraction effect. This work shows that the PDMS layer could be used to reduce thermal noise in high-Q silica microcavities for applications in sensing, lasing, and nonlinear optics.
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42.79.-e Optical elements, devices, and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Coherent anti-Stokes Raman microspectroscopy using spectral focusing with glass dispersion

Israel Rocha-Mendoza, Wolfgang Langbein, and Paola Borri

Appl. Phys. Lett. 93, 201103 (2008); http://dx.doi.org/10.1063/1.3028346 (3 pages) | Cited 21 times

Online Publication Date: 18 November 2008

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We demonstrate experimentally that coherent anti-Stokes Raman microspectroscopy with high spectral resolution is achieved using femtosecond laser pulses chirped up to a few picoseconds by glass elements of known group-velocity dispersion without significant intensity losses. By simply choosing the length of the glass, the chirp of Stokes and pump pulses is tailored to obtain a spectral resolution given by the Fourier limit of the chirped pulse duration. We show that for chirped pulse durations shorter than or comparable to the Raman coherence time, maximum signal occurs for a pump arriving after the Stokes pulse, a time-ordering effect confirmed by numerical simulations.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.47.J- Ultrafast spectroscopy (<1 psec)
81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses

Strain-induced low dimensional confinement structures

Nadir Sekkal and V. R. Velasco

Appl. Phys. Lett. 93, 201104 (2008); http://dx.doi.org/10.1063/1.3030981 (3 pages)

Online Publication Date: 18 November 2008

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We propose here confinement structures similar to heterostructures and superlattices. The present structures can be obtained by applying strain to a single material in a periodic or aperiodic way. The conversion of an indirect gap into an optical active direct or quasidirect gap problem has also been investigated together with the role of zone folding in this phenomenon.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.63.-b Electronic transport in nanoscale materials and structures
73.43.Jn Tunneling
71.70.Fk Strain-induced splitting
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Multiple pulse thermal damage thresholds of materials for x-ray free electron laser optics investigated with an ultraviolet laser

Stefan P. Hau-Riege, Richard A. London, Richard M. Bionta, Regina Soufli, Dmitri Ryutov, Michael Shirk, Sherry L. Baker, Patrick M. Smith, and Pradeep Nataraj

Appl. Phys. Lett. 93, 201105 (2008); http://dx.doi.org/10.1063/1.3021081 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2008

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Optical elements to be used for x-ray free electron lasers (XFELs) must withstand multiple high-fluence pulses. We have used an ultraviolet laser to study the damage of two candidate materials, crystalline Si and B4C-coated Si, emulating the temperature profile expected to occur in optics exposed to XFEL pulses. We found that the damage threshold for 105 pulses is ∼ 20% to 70% lower than the melting threshold.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
41.60.Cr Free-electron lasers
42.79.-e Optical elements, devices, and systems
61.82.Fk Semiconductors

Experimental demonstration of tunable negative phase velocity and negative refraction in a ferromagnetic/ferroelectric composite metamaterial

Hongjie Zhao, Lei Kang, Ji Zhou, Qian Zhao, Longtu Li, Liang Peng, and Yang Bai

Appl. Phys. Lett. 93, 201106 (2008); http://dx.doi.org/10.1063/1.3033397 (3 pages) | Cited 7 times

Online Publication Date: 20 November 2008

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A tunable left-handed transmission is demonstrated experimentally in a ferromagnetic/ferroelectric composite metamaterial (CMM) consisting of an array of yttrium iron garnet (YIG) rods combined with barium strontium titanate (BST) rods. We observed a passband in the CMM within the overlap of the stop bands of YIG rods alone and BST rods alone. Both measured phase velocity and refractive index of the CMM are shown to be negative at the relevant frequency range. The frequency showing left handedness can be adjusted continuously, dynamically, and reversibly by an applied magnetic field with a sensitive response of 3.5 GHz/kOe.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.80.+q Magnetomechanical effects, magnetostriction
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Dd Nonmetallic ferromagnetic materials
77.80.-e Ferroelectricity and antiferroelectricity

Phonon-assisted ultraviolet anti-Stokes photoluminescence from GaN film grown on Si (111) substrate

Suvranta K. Tripathy, Guibao Xu, Xiaodong Mu, Yujie J. Ding, Muhammad Jamil, Ronald A. Arif, Nelson Tansu, and Jacob B. Khurgin

Appl. Phys. Lett. 93, 201107 (2008); http://dx.doi.org/10.1063/1.3030883 (3 pages) | Cited 2 times

Online Publication Date: 20 November 2008

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Phonon-assisted anti-Stokes photoluminescence (ASPL) in the ultraviolet region has been observed in the GaN film grown on a Si (111) substrate. The ASPL peaks are observable only at sufficiently low temperatures. In addition, even if the photon energy is ≈ 318 meV below the transition energy for bound excitons, the ASPL peaks can be still observed. Based on our analysis, the donor-acceptor pairs and bound excitons have played primary roles in the generation of ASPL. Upon the absorption of photons, the ionizations of the neutral donors and neutral acceptors are assisted by longitudinal-optical phonons.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Ponderomotive electron acceleration by polarization-gated surface-enhanced optical fields

Peifen Lu, Jian Wu, Hongxing Qi, and Heping Zeng

Appl. Phys. Lett. 93, 201108 (2008); http://dx.doi.org/10.1063/1.3020711 (3 pages) | Cited 2 times

Online Publication Date: 21 November 2008

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We study ponderomotive electron acceleration with polarization-gated surface-plasmon-resonance enhanced optical fields excited by two counter-incident femtosecond laser pulses. Such a polarization-gated excitation scheme creates an intense linearly polarized high-gradient evanescent field for electron acceleration. The maximum kinetic energy of the accelerated ultrafast electrons is doubled with a symmetric angular distribution about the normal of the metal surface as compared with the conventional one-pulse excitation scheme.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.47.-p Spectroscopy of solid state dynamics
42.25.Ja Polarization
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Magnetic steering of a helicon double layer thruster

C. Charles, R. W. Boswell, W. Cox, R. Laine, and P. MacLellan

Appl. Phys. Lett. 93, 201501 (2008); http://dx.doi.org/10.1063/1.3033201 (3 pages) | Cited 7 times

Online Publication Date: 19 November 2008

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The ion beam generated by a helicon double layer has been electrically steered up to 20° off axis by using a solenoid placed normal to the two axial solenoids of the helicon plasma source without significantly changing the beam exhaust velocity.
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52.75.Di Ion and plasma propulsion
52.27.-h Basic studies of specific kinds of plasmas

Controlled electron injection into laser wakefields with a perpendicular injection laser pulse

W.-M. Wang, Z.-M. Sheng, and J. Zhang

Appl. Phys. Lett. 93, 201502 (2008); http://dx.doi.org/10.1063/1.3020301 (3 pages) | Cited 6 times

Online Publication Date: 20 November 2008

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Electron injection into laser wakefields for acceleration by two orthogonally directed laser pulses is investigated theoretically. It is found that efficient injection occurs provided the two pulses are collinearly polarized, even if the injection pulse is much weaker than the pump pulse driving wakefields. Compared with the head-on colliding injection geometry, this scheme allows for a shorter propagation distance less than a Rayleigh length for the injection pulse, before its overlapping with the pump pulse. Moreover, it can generate electron beams stably with comparable low energy spread and emittance, as demonstrated by particle-in-cell simulations. The optimization of laser parameters is also investigated.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.65.Rr Particle-in-cell method

Directional properties of hard x-ray sources generated by tightly focused ultrafast laser pulses

Bixue Hou, Aghapi Mordovanakis, James Easter, Karl Krushelnick, and John A. Nees

Appl. Phys. Lett. 93, 201503 (2008); http://dx.doi.org/10.1063/1.3023065 (3 pages) | Cited 5 times

Online Publication Date: 20 November 2008

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Directional properties of ultrafast laser-based hard x-ray sources are experimentally studied using tightly focused approximately millijoule laser pulses incident on a bulk Mo target. Energy distributions of Kα and total x rays, as well as source-size distributions are directionally resolved in vacuum and in flowing helium, respectively. Directional distributions of x-ray emission is more isotropic for p-polarized pump than for s-polarized. Based on source-size measurements, a simple two-location model, with expanded plasma and bulk material, is employed to represent the x-ray source profile.
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52.59.Px Hard X-ray sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Ph X-ray, γ-ray, and particle generation
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Polymer stabilized liquid crystal films reflecting both right- and left-circularly polarized light

Jinbao Guo, Hui Cao, Jie Wei, Duowei Zhang, Fang Liu, Guohui Pan, Dongyu Zhao, Wanli He, and Huai Yang

Appl. Phys. Lett. 93, 201901 (2008); http://dx.doi.org/10.1063/1.3003869 (3 pages) | Cited 15 times

Online Publication Date: 17 November 2008

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A single-layer polymer stabilized liquid crystal (PSLC) film reflecting both right- and left-circularly polarized light has been developed by a wash-out/refill method. The PSLC film was achieved by prefabricating the polymer network with a left-handed helical structure and then refilling a cholesteric liquid crystal with a right-handed helical structure into the network. The reflection intensity of the PSLC film is close to 100% when the pitch lengths of the two opposite helical structures are the same. It was demonstrated that the memory effect of the polymer network is an important mechanism for the resulting film properties.
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68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics

A Dnv point group structure possessing complete band gap based on gradual heterostructure and self-simulating sphere

Tianrui Zhai, Zhaona Wang, Rongkuo Zhao, Jing Zhou, Dahe Liu, and Xiangdong Zhang

Appl. Phys. Lett. 93, 201902 (2008); http://dx.doi.org/10.1063/1.3031671 (3 pages) | Cited 4 times

Online Publication Date: 17 November 2008

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A structure with Dnv point group was fabricated by compounding a gradual heterostructure and a self-simulating sphere. The gradual heterostructure has two-dimensional omnidirectional band gap and the self-simulating sphere makes it possess a complete band gap. The experimental results were explained by theoretical analysis. This kind of structure can be implemented using low refractive index materials.
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42.70.Qs Photonic bandgap materials
79.60.Jv Interfaces; heterostructures; nanostructures
71.20.Tx Fullerenes and related materials; intercalation compounds

Ab initio investigation on oxygen defect clusters in UO2+x

Hua Y. Geng, Ying Chen, Yasunori Kaneta, and Motoyasu Kinoshita

Appl. Phys. Lett. 93, 201903 (2008); http://dx.doi.org/10.1063/1.3035846 (3 pages) | Cited 7 times

Online Publication Date: 19 November 2008

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Oxygen defect clustering in uranium dioxide had been indicated in powder neutron diffraction measurements, and an empirical clustering mechanism had been proposed to explain the data. However, using first-principles LSDA+U calculations, we find that this empirical model, in fact, cannot work. A more physically reasonable model is proposed based on a thermodynamical competition between point defects and cuboctahedral clusters. This mechanism interprets the puzzled origin of the observed asymmetric interstitial O′ and O″ naturally. It also gives a good and consistent agreement with all available experimental data, except the high occupation of the O″ site.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jj Interstitials
71.20.Ps Other inorganic compounds

Directional enhanced acoustic radiation caused by a point cavity in a finite-size two-dimensional phononic crystal

Feng-Chia Hsu, Tsung-Tsong Wu, Jin-Chen Hsu, and Jia-Hong Sun

Appl. Phys. Lett. 93, 201904 (2008); http://dx.doi.org/10.1063/1.3033220 (3 pages) | Cited 6 times

Online Publication Date: 19 November 2008

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In this letter, we present results of a study on the directional enhanced radiation generated by a point resonant cavity operating at the band-gap frequency of a two-dimensional finite-size phononic crystal. We find that the directive radiation for operating frequency within the band gap comes from the direction-dependent transmittance property of the square-lattice phononic crystal. The directive-radiation characteristic can be capitalized on enhancing the emission from the phononic crystals by coupling the source with point-defect modes, and the enhanced directive radiation patterns with main lobe width less than 12.9° are demonstrated.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
62.65.+k Acoustical properties of solids
63.20.kp Phonon-defect interactions
61.72.J- Point defects and defect clusters

Segregation of tungsten at γ′(L12)/γ(fcc) interfaces in a Ni-based superalloy: An atom-probe tomographic and first-principles study

Yaron Amouyal, Zugang Mao, and David N. Seidman

Appl. Phys. Lett. 93, 201905 (2008); http://dx.doi.org/10.1063/1.3026745 (3 pages) | Cited 9 times

Online Publication Date: 20 November 2008

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γ(fcc)/γ′(L12) heterophase interfaces in a Ni-based superalloy are investigated using atom-probe tomography and first-principles calculations. Flat {100} interfaces exhibit a confined (nonmonotonic) Gibbsian interfacial excess of tungsten, ΓW = 1.2±0.2 nm−2, corresponding to a 5 mJ m−2 decrease in interfacial free energy. Conversely, no measurable segregation of W is detected at curved interfaces. First-principles calculations for a Ni–Al–W system having a {100} interface indicate a decrease in the interfacial energy of 5 mJ m−2 due to W segregation. Similar calculations for {110} and {111} interfaces predict an increase of 1 and 9 mJ m−2 in their energies, respectively, and therefore no heterophase segregation.
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64.75.Op Phase separation and segregation in alloying
68.35.Md Surface thermodynamics, surface energies

Influence of a bimodal eutectic structure on the plasticity of a (Ti70.5Fe29.5)91Sn9 ultrafine composite

J. H. Han, K. B. Kim, S. Yi, J. M. Park, D. H. Kim, S. Pauly, and J. Eckert

Appl. Phys. Lett. 93, 201906 (2008); http://dx.doi.org/10.1063/1.3029745 (3 pages) | Cited 19 times

Online Publication Date: 20 November 2008

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Systematic investigations on the microstructural evolution of a bimodal eutectic (Ti70.5Fe29.5)91Sn9 ultrafine composite containing Ti3Sn dendrites upon compression reveal that local deformation of the dendrites dominates the early stage of deformation with a plastic strain of εp = 5.8%. After further deformation (εp = 10.2%), a wavy propagation of shear bands indicative of dissipation of the shear stress is caused by a rotation of the coarse eutectic structure along the interfaces of the bimodal eutectic structure.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
68.35.Gy Mechanical properties; surface strains

Nanomechanical thermal analysis of electrospun polymer fibers

Wei Wang, Andrew J. Bushby, and Asa H. Barber

Appl. Phys. Lett. 93, 201907 (2008); http://dx.doi.org/10.1063/1.3033222 (3 pages) | Cited 9 times

Online Publication Date: 20 November 2008

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Thermomechanical properties of individual electrospun semicrystalline polyethylene oxide (PEO) fibers were measured using atomic force microscopy based indentation. Fibers showed a higher elastic modulus than corresponding films despite a lower crystallinity, indicating significant molecular alignment along the principle fiber axis. Heating of the fibers gave a progressive loss in elastic modulus highlighting a dominant amorphous thermomechanical response. This is in contrast to softening of an amorphous phase and melting of a crystalline phase in semicrystalline bulk PEO films.
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81.40.Gh Other heat and thermomechanical treatments
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.60.Bs Mechanical and acoustical properties
62.20.de Elastic moduli
62.20.Qp Friction, tribology, and hardness

Polarity driven formation of InAs/GaAs hierarchical nanowire heterostructures

Mohanchand Paladugu, Jin Zou, Ya-Nan Guo, Xin Zhang, Hannah J. Joyce, Qiang Gao, H. Hoe Tan, C. Jagadish, and Yong Kim

Appl. Phys. Lett. 93, 201908 (2008); http://dx.doi.org/10.1063/1.3033551 (3 pages) | Cited 16 times

Online Publication Date: 20 November 2008

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The structural and morphological characteristics of InAs/GaAs radial nanowire heterostructures were investigated using transmission electron microscopy. It has been found that the radial growth of InAs was preferentially initiated on the {112}A sidewalls of GaAs nanowires. This preferential deposition leads to extraordinarily asymmetric InAs/GaAs radial nanowire heterostructures. Such formation of radial nanowire heterostructures provides an opportunity to engineer hierarchical nanostructures, which further widens the potential applications of semiconductor nanostructures.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
62.23.Hj Nanowires
68.37.Lp Transmission electron microscopy (TEM)

Why so strong for the lotus leaf?

Zhiguang Guo, Weimin Liu, and Bao-Lian Su

Appl. Phys. Lett. 93, 201909 (2008); http://dx.doi.org/10.1063/1.3036535 (3 pages) | Cited 9 times

Online Publication Date: 21 November 2008

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The authors discussed the potential reasons why the lotus leaf is so strong by means of scanning electron microscopy (SEM). The results showed that the good mechanical properties of lotus leaf should be attributed to its architecture, such as paralleled microtubes structure, umbrellalike structure, and hierarchically layered hexagon structure. The important observation from this work is that the surface of the rear face of the lotus leaf seems to be constituted by the layers of hexagons whose hierarchical pilling up of size decreases as we go deeper from surface. This is a typical fractal-like phenomenon.
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87.17.Rt Cell adhesion and cell mechanics

Characterizing the global dispersion of carbon nanotubes in ceramic matrix nanocomposites

Orsolya Koszor, Levente Tapasztó, Márton Markó, and Csaba Balázsi

Appl. Phys. Lett. 93, 201910 (2008); http://dx.doi.org/10.1063/1.3029746 (3 pages) | Cited 3 times

Online Publication Date: 21 November 2008

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The dispersion of single-walled carbon nanotubes in silicon nitride ceramic matrices has been investigated by small angle neutron scattering experiments. In contrast to electron microscopy investigations of fracture surfaces, neutron scattering measurements provide information on the bulk dispersion of nanotubes within the matrix. The scattering intensities reveal a decay exponent characteristic to surface fractals, which indicates that the predominant part of nanotubes can be found in loose networks surrounding the grains of the polycrystalline matrix.
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81.05.Mh Cermets, ceramic and refractory composites
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.25.Mn Fracture/brittleness
61.46.-w Structure of nanoscale materials
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Experimental determination of valence band offset at PbTe/CdTe(111) heterojunction interface by x-ray photoelectron spectroscopy

Jianxiao Si, Shuqiang Jin, Hanjie Zhang, Ping Zhu, Dongjiang Qiu, and Huizhen Wu

Appl. Phys. Lett. 93, 202101 (2008); http://dx.doi.org/10.1063/1.3028028 (3 pages) | Cited 6 times

Online Publication Date: 17 November 2008

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Lattice-matched PbTe/CdTe(111) heterojunction interfaces were studied using x-ray photoelectron spectroscopy. A type-I band alignment with a valence band offset of ΔEV = 0.135±0.05 eV and a conduction band offset of ΔEC = 1.145±0.05 eV is concluded. Within experimental error the determined valence band offset is in agreement with theoretical prediction by inclusion of spin-orbit interaction.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Advanced luminescence based effective series resistance imaging of silicon solar cells

H. Kampwerth, T. Trupke, J. W. Weber, and Y. Augarten

Appl. Phys. Lett. 93, 202102 (2008); http://dx.doi.org/10.1063/1.2982588 (3 pages) | Cited 19 times

Online Publication Date: 18 November 2008

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A technique for fast and spatially resolved measurement of the effective series resistance of silicon solar cells from luminescence images is introduced. Without compromising the speed of existing luminescence based series resistance imaging methods, this method offers significant advantages in that it is more robust against variations in local diode characteristics. Lateral variations in the series resistance of an industrial screen printed multicrystalline silicon solar cell obtained from this method show excellent correlation with a Corescan measurement and are also shown to be unaffected by lateral variations in the diode properties.
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84.60.Jt Photoelectric conversion

Low specific contact resistance of heavily phosphorus-doped diamond film

Hiromitsu Kato, Hitoshi Umezawa, Norio Tokuda, Daisuke Takeuchi, Hideyo Okushi, and Satoshi Yamasaki

Appl. Phys. Lett. 93, 202103 (2008); http://dx.doi.org/10.1063/1.3005639 (3 pages) | Cited 15 times

Online Publication Date: 18 November 2008

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Low resistive contacts were formed on heavily phosphorus-doped diamond (n+) films with phosphorus concentration of over ∼ 1020 cm−3 grown on (111) diamond substrates by microwave plasma enhanced chemical vapor deposition with precise control of growth conditions. The specific contact resistance was determined by characterizing the current-voltage relations by means of transfer length method. It was found that the resistance of Ti/n+ contact was significantly reduced down to the order of ∼ 10−3 Ω cm2 even at room temperature, which indicates that the barrier width would be narrow for tunneling through the barrier to take place by heavy phosphorus doping.
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73.40.Cg Contact resistance, contact potential
73.40.Gk Tunneling
61.72.up Other materials
73.40.Ns Metal-nonmetal contacts
81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Polarization-induced two-dimensional electron gases in ZnMgO/ZnO heterostructures

H. Tampo, H. Shibata, K. Maejima, A. Yamada, K. Matsubara, P. Fons, S. Kashiwaya, S. Niki, Y. Chiba, T. Wakamatsu, and H. Kanie

Appl. Phys. Lett. 93, 202104 (2008); http://dx.doi.org/10.1063/1.3028338 (3 pages) | Cited 19 times

Online Publication Date: 18 November 2008

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Both the formation mechanism and the origin of the two-dimensional electron gas (2DEG) in ZnMgO/ZnO heterostructures have been investigated. The 2DEG in the heterostructures was confirmed to originate from polarization-induced charge and was found to be dominant for transport at low temperatures as well as room temperature (RT) by transport measurements. The origin of 2DEG was concluded to be the surface of the ZnMgO layer based on both capacitance-voltage measurements and the dependence of the carrier concentration on the ZnMgO layer thickness. The largest sheet carrier concentration was 1.1×1013 cm−2 and the highest mobility for the heterostructure was obtained for a Mg composition of 0.61 at RT.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
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