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16 Jun 2003

Volume 82, Issue 24, pp. 4215-4390

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages)

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin
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High-conductivity n-AlGaN with high Al mole fraction grown by metalorganic vapor phase deposition

M. Pophristic, S. P. Guo, and B. Peres

Appl. Phys. Lett. 82, 4289 (2003); http://dx.doi.org/10.1063/1.1582377 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2003

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Highly-conductive and crack-free n-Al0.6Ga0.4N films with thickness up to 1 μm were achieved by using high-temperature AlN or AlGaN/AlN superlattice (SL) buffer layers. Room-temperature Hall measurements show the highest electron concentration of 3.5×1018 cm−3 with mobility of 25 cm2/V s. Electron mobility was increased from 25 to 35 cm2/V s by introducing the AlGaN/AlN SL buffer layer. Second ion mass spectroscopy indicates that there is high oxygen doping concentration in the film, and that the film resistivity decreases with increasing oxygen concentration from 1×1017 to ∼ 1×1019 cm−3. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
72.80.Ey III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Dn Low-field transport and mobility; piezoresistance

Photocurrent noise in multi-quantum-well infrared photodetectors

A. Carbone, R. Introzzi, and H. C. Liu

Appl. Phys. Lett. 82, 4292 (2003); http://dx.doi.org/10.1063/1.1581388 (3 pages) | Cited 8 times

Online Publication Date: 10 June 2003

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We report on photocurrent noise in AlGaAs/GaAs quantum-well infrared photodetectors having nominally the same design, except the number of wells N. The power spectral density does not scale as the inverse of the number of wells N in the presence of infrared radiation. These features can be understood by taking into account the nonlinearity arising at high infrared power as a consequence of the nonuniform potential distribution through the quantum-well structure. © 2003 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Td Noise processes and phenomena
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.50.Pz Photoconduction and photovoltaic effects

Epitaxial colossal magnetoresistive La0.67(Sr,Ca)0.33MnO3 films on Si

J.-H. Kim, S. I. Khartsev, and A. M. Grishin

Appl. Phys. Lett. 82, 4295 (2003); http://dx.doi.org/10.1063/1.1583133 (3 pages) | Cited 30 times

Online Publication Date: 10 June 2003

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La0.67(Sr,Ca)0.33MnO3 (LSCMO) films have been grown by a pulsed-laser deposition technique on Si(001) substrates buffered with Bi4Ti3O12/CeO2/yttrium-stabilized zirconia (YSZ) heteroepitaxial layers. X-ray diffraction has revealed cube-on-cube growth of an epitaxial Bi4Ti3O12/CeO2/YSZ/Si heterostructure whereas the LSCMO layer grows in the “diagonal-on-side” manner on top of the Bi4Ti3O12 (BTO) template. The maximum temperature coefficient of resistivity (TCR)=4.4% K−1 and colossal magnetoresistance (CMR) Δρ/ρ∼2.9% kOe−1 have been reached at 294 K. This was achieved due to the successive improvement of c-axis orientation of the layers: Full widths at half-maximum 0.65°, 0.58°, 0.65°, 1.13°, and 0.18° in LSCMO/BTO/CeO2/YSZ/Si stack, respectively. As a prototype of an uncooled bolometer, heteroepitaxial CMR structure on Si demonstrates, at 294 K, the noise equivalent temperature difference of 1.2 μK/√Hz@30 Hz. © 2003 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
68.55.A- Nucleation and growth
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.80.Jc Other crystalline inorganic semiconductors
81.05.Hd Other semiconductors
81.15.Fg Pulsed laser ablation deposition
73.50.Dn Low-field transport and mobility; piezoresistance

First-principles study of n-type dopants and their clustering in SiC

R. Rurali, P. Godignon, J. Rebollo, E. Hernández, and P. Ordejón

Appl. Phys. Lett. 82, 4298 (2003); http://dx.doi.org/10.1063/1.1583870 (3 pages) | Cited 11 times

Online Publication Date: 10 June 2003

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We report the results of an ab initio study of N and P dopants in SiC. We find that while N substitutes most favorably at a C lattice site, P does so preferably at a Si site, except in n-doping and Si-rich 3C-SiC. Furthermore, we consider a series of dopant complexes that could form in high-dose implantation, in order to investigate the dopant activation behavior in this limit. We find that all N complexes considered lead to passivation through the formation of a deep level. For P, the most stable aggregate is still an active dopant, while passivation is only observed for complexes with a higher formation energy. We discuss how these results could help in the understanding of the observed experimental high-dose doping and codoping behavior of these species. © 2003 American Institute of Physics.
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61.72.up Other materials
71.55.Ht Other nonmetals
61.72.S- Impurities in crystals
61.80.Jh Ion radiation effects

Enhancement of Schottky barrier height on AlGaN/GaN heterostructure by oxidation annealing

Chang Min Jeon and Jong-Lam Lee

Appl. Phys. Lett. 82, 4301 (2003); http://dx.doi.org/10.1063/1.1583140 (3 pages) | Cited 19 times

Online Publication Date: 10 June 2003

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The effect of preannealing of AlGaN under an oxygen ambient on the improvement of the Schottky barrier height on an AlGaN/GaN heterostructure was studied using synchrotron radiation photoemission spectroscopy. The oxidation annealing increased the Schottky barrier height from 0.59 to 0.84 eV, and dramatically reduced the reverse leakage current. The group-III elements (Ga, Al) outdiffused to the surface to form group-III oxides during the annealing, leaving group-III vacancies behind. The surface Fermi level shifted to the energy levels of group-III vacancies, leading to the enhancement of Schottky properties of AlGaN. © 2003 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
79.60.Jv Interfaces; heterostructures; nanostructures
61.72.J- Point defects and defect clusters

Metal–oxide–semiconductor devices using Ga2O3 dielectrics on n-type GaN

Ching-Ting Lee, Hong-Wei Chen, and Hsin-Ying Lee

Appl. Phys. Lett. 82, 4304 (2003); http://dx.doi.org/10.1063/1.1584520 (3 pages) | Cited 52 times

Online Publication Date: 10 June 2003

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Using a photoelectrochemical method involving a He–Cd laser, Ga2O3 oxide layers were directly grown on n-type GaN. We demonstrated the performance of the resultant metal–oxide–semiconductor devices based on the grown Ga2O3 layer. An extremely low reverse leakage current of 200 pA was achieved when devices operated at −20 V. Furthermore, high forward and reverse breakdown electric fields of 2.80 MV/cm and 5.70 MV/cm, respectively, were obtained. Using a photoassisted current–voltage method, a low interface state density of 2.53×1011 cm−2 eV−1 was estimated. The varactor devices permit formation of inversion layers, so that they may be applied for the fabrication of metal–oxide–semiconductor field-effect transistors. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
73.61.Ey III-V semiconductors
81.65.Mq Oxidation
77.22.Jp Dielectric breakdown and space-charge effects
81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
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High-coercivity ultralight transparent magnets

M. Gich, Ll. Casas, A. Roig, E. Molins, J. Sort, S. Suriñach, M. D. Baró, J. S. Muñoz, L. Morellon, M. R. Ibarra, and J. Nogués

Appl. Phys. Lett. 82, 4307 (2003); http://dx.doi.org/10.1063/1.1578538 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2003

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Magnetic silica-aerogel composites have been synthesized by dispersing hard magnetic Nd2Fe14B particles in a sol during a fast sol-gel process and subsequently supercritically drying the resulting gels. The composites are found to retain most of the outstanding properties of their constituents: the large coercivity and moderate remanence of the magnetic powders and the transparency and low density of silica aerogels. Moreover, aerogels synthesized in the presence of a magnetic field exhibit the alignment of the particles, forming needle-like structures along the direction of the applied magnetic field, which results in optical and magnetic anisotropies. Due to their unique combination of properties, these types of materials may be appealing for magneto-optics and magnetic actuator applications. © 2003 American Institute of Physics.
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81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.50.Tt Fine-particle systems; nanocrystalline materials
81.05.Mh Cermets, ceramic and refractory composites
75.50.Vv High coercivity materials
82.70.Gg Gels and sols
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

In1−xMnxSb—a narrow-gap ferromagnetic semiconductor

T. Wojtowicz, G. Cywiński, W. L. Lim, X. Liu, M. Dobrowolska, J. K. Furdyna, K. M. Yu, W. Walukiewicz, G. B. Kim, M. Cheon, X. Chen, S. M. Wang, and H. Luo

Appl. Phys. Lett. 82, 4310 (2003); http://dx.doi.org/10.1063/1.1583142 (3 pages) | Cited 33 times

Online Publication Date: 10 June 2003

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A narrow-gap ferromagnetic In1−xMnxSb semiconductor alloy was grown by low-temperature molecular-beam epitaxy on CdTe/GaAs hybrid substrates. Ferromagnetic order in In1−xMnxSb was unambiguously established by the observation of clear hysteresis loops both in direct magnetization measurements and in the anomalous Hall effect, with Curie temperatures TC ranging up to 8.5 K. The observed values of TC agree well with the existing models of carrier-induced ferromagnetism. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Sensitive detection of irreversible switching in a single FePt nanosized dot

N. Kikuchi, S. Okamoto, O. Kitakami, Y. Shimada, and K. Fukamichi

Appl. Phys. Lett. 82, 4313 (2003); http://dx.doi.org/10.1063/1.1580994 (3 pages) | Cited 37 times

Online Publication Date: 10 June 2003

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Magnetization of an isolated single dot as small as 60 nm in diameter fabricated from a single crystal L10-FePt(001) film has been measured by detection of the anomalous Hall effect in the temperature range from 10 to 300 K. Over the whole temperature range, the dots with diameter ranging from 60 nm to 12 μm exhibit perfect rectangular magnetization loops with coercivity almost constant regardless of the very large difference in diameter. The activation energy has been evaluated to be about 4×10−19 J, equivalent to the domain-wall energy times the square of the domain-wall thickness, suggesting that the magnetization reversals are initiated by nucleation of reversed embryo with the dimension of the exchange length. © 2003 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Et Exchange and superexchange interactions
75.47.Np Metals and alloys

Experimental probing of the anisotropy of the empty p states near the Fermi level in MgB2

R. F. Klie, Y. Zhu, G. Schneider, and J. Tafto

Appl. Phys. Lett. 82, 4316 (2003); http://dx.doi.org/10.1063/1.1583132 (3 pages) | Cited 10 times

Online Publication Date: 10 June 2003

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We have studied the boron K edge in the superconductor MgB2 by electron energy loss spectroscopy (EELS) and experimentally resolved the empty p states at the Fermi level that have previously been observed within an energy window of 0.8 eV by soft x-ray absorption spectroscopy. Using angular-resolved EELS, we find that these states at the immediate edge onset have pxy character in agreement with predictions from first-principle electronic structure calculations. © 2003 American Institute of Physics.
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74.25.Jb Electronic structure (photoemission, etc.)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Thickness dependence of the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition

A. V. Pogrebnyakov, J. M. Redwing, J. E. Jones, X. X. Xi, S. Y. Xu, Qi Li, V. Vaithyanathan, and D. G. Schlom

Appl. Phys. Lett. 82, 4319 (2003); http://dx.doi.org/10.1063/1.1583852 (3 pages) | Cited 56 times

Online Publication Date: 10 June 2003

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We have studied the effect of deposition rate and layer thickness on the properties of epitaxial MgB2 thin films grown by hybrid physical-chemical vapor deposition on 4H-SiC substrates. The MgB2 film deposition rate depends linearly on the concentration of B2H6 in the inlet gas mixture. We found that the superconducting and normal-state properties of the MgB2 films are determined by the film thickness, not by the deposition rate. When the film thickness was increased, the transition temperature Tc increased and the residual resistivity ρ0 decreased. Above 3000 Å, a Tc of 41.8 K, a ρ0 of 0.28 μΩ cm, and a residual resistance ratio RRR of over 30 were obtained. © 2003 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
74.62.Yb Other effects
74.25.F- Transport properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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Nanoscale polarization manipulation and conductance switching in ultrathin films of a ferroelectric copolymer

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages) | Cited 39 times

Online Publication Date: 10 June 2003

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We report the direct observation of induced molecular reorientation on a ferroelectric copolymer with a scanning tunneling microscope (STM). Ultrathin copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%) revealed a quasihexagonal close-packing structure with long-range polymer chain ordering. By flipping the polarity of the STM tip bias voltage, a reversal of local polarization was observed through an apparent lattice shift and was accompanied by an asymmetric “diode-like” character in tunneling current I(V). These results clearly demonstrated conductance switching behavior on nanoscale with local polarization reversal. © 2003 American Institute of Physics.
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77.84.Jd Polymers; organic compounds
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
68.55.-a Thin film structure and morphology

Ferroelectric properties of (Ba0.5Sr0.5)TiO3/Pb(Zr0.52Ti0.48)O3/ (Ba0.5Sr0.5)TiO3 thin films with platinum electrodes

Feng Yan, Yening Wang, Helen L. W. Chan, and Chung Loong Choy

Appl. Phys. Lett. 82, 4325 (2003); http://dx.doi.org/10.1063/1.1583137 (3 pages) | Cited 17 times

Online Publication Date: 10 June 2003

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Multilayered Pt/(Ba0.5Sr0.5)TiO3/Pb(Zr0.52Ti0.48)O3/(Ba0.5Sr0.5)TiO3/Pt (BST/PZT/BST) thin films with different thicknesses of the BST layers were prepared by the pulsed-laser deposition method. The existence of a BST layer between the PZT and Pt electrode can greatly improve the fatigue properties of the PZT film. However, the heterostructure with thicker BST layers exhibits lower remnant polarization because of a lower electric field applied on the PZT layer. So, the thickness of BST layers should be decreased to decrease the working voltage of the multilayered film. A heterostructure with very thin BST layers (thickness ∼7.5 nm) has good ferroelectric properties, such as high remnant polarization and rare fatigue resistance after 1010 switching cycles. A possible reason for the effect of BST is that the BST layer can absorb oxygen vacancies or other point defects from the PZT layer and greatly improve its fatigue properties. © 2003 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Supercritical carbon dioxide extraction of porogens for the preparation of ultralow-dielectric-constant films

T. Rajagopalan, B. Lahlouh, J. A. Lubguban, N. Biswas, S. Gangopadhyay, J. Sun, D. H. Huang, S. L. Simon, A. Mallikarjunan, H.-C. Kim, W. Volksen, M. F. Toney, E. Huang, P. M. Rice, E. Delenia, et al.

Appl. Phys. Lett. 82, 4328 (2003); http://dx.doi.org/10.1063/1.1583139 (3 pages) | Cited 12 times

Online Publication Date: 10 June 2003

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Supercritical carbon dioxide extraction of poly(propylene glycol) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen, is demonstrated to produce nanoporous, ultralow-dielectric-constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. 25 and 55 wt % porogen loads were investigated in the present work. Structural characterization of the samples conducted using transmission electron microscope, small angle x-ray scattering, and Fourier transform infrared spectroscopy, confirms the extraction of the porogen from the PMSSQ matrix at relatively low temperatures (⩽200 °C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 °C–450 °C). The values of dielectric constants and refractive indices measured are in good agreement with the structural properties of these samples. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
81.05.Rm Porous materials; granular materials
77.22.Ch Permittivity (dielectric function)
77.84.Jd Polymers; organic compounds
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
78.66.Qn Polymers; organic compounds
81.07.Pr Organic-inorganic hybrid nanostructures

Effects of interfacial nitrogen on the structural and electrical properties of ultrathin ZrO2 gate dielectrics on partially strain-compensated SiGeC/Si heterolayers

R. Mahapatra, S. Maikap, Je-Hun Lee, G. S. Kar, A. Dhar, Nong-M. Hwang, Doh-Y. Kim, B. K. Mathur, and S. K. Ray

Appl. Phys. Lett. 82, 4331 (2003); http://dx.doi.org/10.1063/1.1583143 (3 pages) | Cited 3 times

Online Publication Date: 10 June 2003

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The interfacial characteristics of high-κ ZrO2 on O2 and N2O-plasma-treated Si0.69Ge0.3C0.01 surfaces have been investigated using secondary ion mass spectroscopy and x-ray photoelectron spectroscopy. N2O-plasma-treated films show the formation of a nitrogen-rich Zr–germano–silicate interfacial layer between the deposited ZrO2 and SiGeC films. The N-treated film has a higher accumulation capacitance (∼1200 pF), lower leakage current density (7×10−9 A/cm2−1 V), higher breakdown field (∼11 MV/cm), and higher interfacial layer dielectric constant (∼10) than that of the non-nitrogen-treated films. Relatively lower positive trap charge generated by a constant current stressing in N-incorporated dielectric films makes it attractive for scaled metal–oxide–semiconductor field-effect transistor applications. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
79.60.Jv Interfaces; heterostructures; nanostructures
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Role of extrinsic atoms on the morphology and field emission properties of carbon nanotubes

L. H. Chan, K. H. Hong, D. Q. Xiao, W. J. Hsieh, S. H. Lai, H. C. Shih, T. C. Lin, F. S. Shieu, K. J. Chen, and H. C. Cheng

Appl. Phys. Lett. 82, 4334 (2003); http://dx.doi.org/10.1063/1.1579136 (3 pages) | Cited 29 times

Online Publication Date: 10 June 2003

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Extrinsic atoms were doped into multiwalled carbon nanotubes (MWCNTs) using microwave plasma-enhanced chemical vapor deposition. Doped nitrogen atoms alter the original parallel graphenes into highly curved ones including some fullerene-like structures. Doped nitrogen atoms could replace carbon atoms in MWCNTs and therefore increase the electronic density that enhances the electron field emission properties. On the other hand, the incorporation of boron into the carbon network apparently increases the concentration of electron holes that become electron traps and eventually impedes the electron field emission properties. Fowler–Nordheim plots show two different slopes in the curve, indicating that the mechanism of field emission is changed from low to high bias voltages. β values could be increased by an amount of 42% under low bias voltages and 60% under high bias voltages in the N-doped MWCNTs, but decreased by an amount of 8% under low bias region and 68% under high bias voltage in the B-doped MWCNTs. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
79.70.+q Field emission, ionization, evaporation, and desorption

Self-embedded nanocrystalline chromium carbides on well-aligned carbon nanotips

C. L. Tsai, J. H. Hsu, and C. F. Chen

Appl. Phys. Lett. 82, 4337 (2003); http://dx.doi.org/10.1063/1.1579867 (3 pages) | Cited 4 times

Online Publication Date: 10 June 2003

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Well-aligned carbon nanotips embedded with nanocrystalline chromium carbide were directly grown on a substrate by microwave plasma chemical vapor deposition. These nanomaterials grew up to about 1 μm long and 60 nm in diameter, yielding a high aspect ratio. In comparison between carbon nanotubes with hollow structure, transmission electron microscopy images show its solid body, which is made of graphite along with nanocrystalline chromium carbide on the tip. These nanomaterials perform well in field emission applications with a turn-on field of 1.38 V/μm and 565 μA/cm2 at 2.2 V/μm. Our result confirms the possibility of the self-embedded nanocrystalline materials on the top of carbon nanotips. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
52.77.Dq Plasma-based ion implantation and deposition

II–VI quantum dot formation induced by surface energy change of a strained layer

F. Tinjod, B. Gilles, S. Moehl, K. Kheng, and H. Mariette

Appl. Phys. Lett. 82, 4340 (2003); http://dx.doi.org/10.1063/1.1583141 (3 pages) | Cited 56 times

Online Publication Date: 10 June 2003

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A method for growing self-assembled II–VI quantum dots (QDs) is demonstrated: A highly strained CdTe layer, grown onto Zn(Mg)Te, is covered with an amorphous Te layer which is then desorbed. This induces QD formation, observed as an abrupt change of both the reflection high-energy electron diffraction pattern and the surface morphology studied by atomic force microscopy in an ultrahigh vacuum. The dots are also characterized after capping by microphotoluminescence. This morphology transition, which occurs after and not during the growth, can be understood in terms of variation of the surface energy in presence of the group-VI element, which compensates for the natural trend toward plastic relaxation in II–VI compounds. This method shows the strong influence of the surface energy (and not just the lattice mismatch) in inducing the formation of coherent islands for mismatched systems having a low dislocation formation energy such as CdTe/ZnTe and CdSe/ZnSe. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Dz II-VI semiconductors
68.35.Md Surface thermodynamics, surface energies
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.A- Nucleation and growth
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Dn Self-assembly
68.55.-a Thin film structure and morphology

Effect of Si delta doping on the luminescence properties of InP/InAlP quantum dots

X. B. Zhang, R. D. Heller, M. S. Noh, R. D. Dupuis, G. Walter, and N. Holonyak

Appl. Phys. Lett. 82, 4343 (2003); http://dx.doi.org/10.1063/1.1582364 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2003

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We show that the cathodoluminescence (CL) properties of InP quantum dots (QDs) grown on In0.5Al0.5P matrix layers, lattice-matched to (001) GaAs substrates, can be greatly improved by introducing silicon delta doping in the layer adjacent to the QDs. Under optimized conditions, the room-temperature CL intensity of QDs can be improved by ∼ 16 times. We speculate that the increased CL intensity is caused by the efficient capture of electrons from the reservoir of the delta-doped layer into the QDs, which, to some extent, counterbalances the thermal escape of electrons from the QDs. A temperature-dependent CL study of InP QDs grown without Si delta doping shows a quenching of the CL at high temperatures, which supports the unipolar escape of electrons from QDs, while delta-doped QDs show an anomalous behavior. The QD integrated CL intensity increases with temperature and then decreases after 200 K. This anomalous behavior is interpreted as caused by competition between two processes: (1) thermal activation of carriers out of the potential well introduced by delta doping and then capture by QDs, which enhances the CL intensity; and (2) quenching of the CL due to thermal activation of carriers out of the QDs. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.60.Hk Cathodoluminescence, ionoluminescence

Dilute LaB6 nanoparticles in polymer as optimized clear solar control glazing

Stefan Schelm and Geoff B. Smith

Appl. Phys. Lett. 82, 4346 (2003); http://dx.doi.org/10.1063/1.1584092 (3 pages) | Cited 37 times

Online Publication Date: 10 June 2003

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Window samples with a LaB6 nanoparticle-doped polymer laminate were tested for their performances in the reduction of solar heat gain. The near-infrared absorption, caused by the excitation of surface plasmons, was modeled using an average ellipsoid approach, including a size-induced broadening of the Drude part of the dielectric function. The resonance positions are well reproduced by this method and the size effect broadens the bulk resonance to an extent observed in the sample spectra. Additional broadening and spectral features observed in the absorption of the samples are attributed to shape and orientation effects. © 2003 American Institute of Physics.
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42.79.Ek Solar collectors and concentrators
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.-j Infrared and Raman spectra
61.46.-w Structure of nanoscale materials

Controlled self-assembly of semiconductor quantum dots using shadow masks

T. Schallenberg, T. Borzenko, G. Schmidt, M. Obert, G. Bacher, C. Schumacher, G. Karczewski, L. W. Molenkamp, S. Rodt, R. Heitz, and D. Bimberg

Appl. Phys. Lett. 82, 4349 (2003); http://dx.doi.org/10.1063/1.1584511 (3 pages) | Cited 7 times

Online Publication Date: 10 June 2003

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An effective method for controlling the position and number of self-assembled quantum dots (QDs) grown by molecular-beam epitaxy has been developed. Epitaxially grown shadow masks are used to realize selective area growth, which exploits different incidence angles of the molecular beams. We applied this method to control the position and number of self-assembled CdSe QDs in a ZnSe matrix. Bright cathodoluminescence shows the presence of regularly distributed ensembles of QDs and that single QDs can be reliably grown. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.66.Hf II-VI semiconductors
81.07.Ta Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
81.05.Dz II-VI semiconductors
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Nd Micro- and nanolithography

Fabrication of monodispersive FePt nanoparticle films stabilized on rigid substrates

Andrew C. C. Yu, Mikihisa Mizuno, Yuichi Sasaki, Makoto Inoue, Hirofumi Kondo, Ippei Ohta, David Djayaprawira, and Migaku Takahashi

Appl. Phys. Lett. 82, 4352 (2003); http://dx.doi.org/10.1063/1.1584791 (3 pages) | Cited 33 times

Online Publication Date: 10 June 2003

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Monodispersive FePt nanoparticle films can be stabilized firmly on rigid Si substrates using amino-functional silane, such as [3-(2-aminoethlyamino) propyl]trimethoxysilane, as a coupling layer. The Si substrate/SiO2/APTS/FePt nanoparticles heterostructure was confirmed using high-resolution electron microscopy (HREM). The HREM result agreed well with the x-ray reflectivity measurement upon the individual layer thickness. The as-made superparamagnetic FePt nanoparticle film transformed from chemically disordered fcc structure to chemically ordered L10 phase upon annealing at 800 °C for 30 min under a vacuum of 10−8 Torr. Plan-view high-resolution scanning electron microscopy (HRSEM) observation indicated that under high-vacuum annealing, coalescence of the monodispersive nanoparticle film was not significant. The HRSEM result was consistent with the in-plane x-ray diffractometry measurement, in which sharpening of the diffraction peaks occurred only very slightly for the annealed films. © 2003 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
68.55.-a Thin film structure and morphology
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing

Electron localization by self-assembled GaSb/GaAs quantum dots

M. Hayne, J. Maes, S. Bersier, V. V. Moshchalkov, A. Schliwa, L. Müller-Kirsch, C. Kapteyn, R. Heitz, and D. Bimberg

Appl. Phys. Lett. 82, 4355 (2003); http://dx.doi.org/10.1063/1.1583853 (3 pages) | Cited 19 times

Online Publication Date: 10 June 2003

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We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes. © 2003 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Schottky nanocontacts on ZnO nanorod arrays

W. I. Park, Gyu-Chul Yi, J.-W. Kim, and S.-M. Park

Appl. Phys. Lett. 82, 4358 (2003); http://dx.doi.org/10.1063/1.1584089 (3 pages) | Cited 149 times

Online Publication Date: 10 June 2003

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We report on fabrication and electrical characteristics of ZnO nanorod Schottky diode arrays. High quality ZnO nanorods were grown for the fabrication of the Schottky diodes using noncatalytic metalorganic vapor phase epitaxy and Au was evaporated on the tips of the vertically well-aligned ZnO nanorods. I–V characteristics of both bare ZnO and Au/ZnO heterostructure nanorod arrays were measured using current-sensing atomic force microscopy. Although both nanorods exhibited nonlinear and asymmetric I–V characteristic curves, Au/ZnO heterostructure nanorods demonstrated much improved electrical characteristics: the reverse-bias breakdown voltage was improved from −3 to −8 V by capping a Au layer on the nanorod tips. The origin of the enhanced electrical characteristics for the heterostructure nanorods is suggested. © 2003 American Institute of Physics.
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85.35.-p Nanoelectronic devices
85.30.Hi Surface barrier, boundary, and point contact devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.07.Bc Nanocrystalline materials
73.61.Ga II-VI semiconductors
85.30.Kk Junction diodes
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Impact of Si doping on radio frequency dispersion in unpassivated GaN/AlGaN/GaN high-electron-mobility transistors grown by plasma-assisted molecular-beam epitaxy

Oleg Mitrofanov, Michael Manfra, and Nils Weimann

Appl. Phys. Lett. 82, 4361 (2003); http://dx.doi.org/10.1063/1.1582373 (3 pages) | Cited 23 times

Online Publication Date: 10 June 2003

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We report on the effect of Si doping on the transient behavior of unpassivated high-power GaN/AlGaN/GaN high-electron-mobility transistors grown by plasma-assisted molecular-beam epitaxy on 6H–SiC. The incorporation of Si into the heterostructure barrier is found to reduce the level of radio frequency dispersion as compared to undoped structures. In some devices which incorporate Si doping of the barrier, the pulsed and steady-state current–voltage characteristics coincide, and gate lag is found to be insignificant. More typically, ∼90% of the dc value of drain current is restored at 1 μs after pulsing the gate from pinch off to VGS = 0 V. Significant gate lag is observed in devices that are not doped with Si. In the undoped structure, the drain current reaches only ∼70% of the dc value within 1 μs. The transient behavior in the two designs is attributed to the same defect state with activation energy of 0.22 eV. Dispersion reduction is correlated with an increase of gate leakage current in Si-doped devices. © 2003 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Mx High-frequency effects; plasma effects
73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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