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19 May 2003

Volume 82, Issue 20, pp. 3379-3570

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 3266 (2003); http://dx.doi.org/10.1063/1.1572970 (3 pages)

Michael Mück, Christian Welzel, and John Clarke
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Bleached state transmittance in charge-unbalanced all-solid-state electrochromic devices

Kwang-Soon Ahn, Yoon-Chae Nah, Jin-Young Park, Yung-Eun Sung, Ki-Yun Cho, Seung-Shik Shin, and Jung-Ki Park

Appl. Phys. Lett. 82, 3379 (2003); http://dx.doi.org/10.1063/1.1575927 (3 pages) | Cited 16 times

Online Publication Date: 12 May 2003

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The bleached state transmittance of a charge-unbalanced, complementary electrochromic (EC) device may show residual coloration due to the presence of residual charges. In this study, EC devices were fabricated with configurations G/ITO/Ni(OH)2/Ta2O5/H+–SPE/Ta2O5/WO3/ITO/G and G/ITO/NiOOH/Ta2O5/H+–SPE/Ta2O5/HWO3/ITO/G (G = glass, H+–SPE = proton-conducting solid polymer electrolytes, and ITO = indium tin oxide). These devices, referred to as EC1 and EC2, were initially fabricated from fully bleached EC layers and from fully colored EC layers, respectively. The change in electrochromic properties as a function of charge capacity ratio (R) for each device was then compared. In comparison to EC2 devices, EC1 devices provided better bleached-state transmittances and higher coloration efficiencies over a wider range of R, and were less sensitive to changes in R value. This may arise because the absorbance caused by the residual charges in the colored state is greater and more sensitive to the charge capacity ratio than that in the bleached state. © 2003 American Institute of Physics.
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78.20.Jq Electro-optical effects
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.79.-e Optical elements, devices, and systems

Simulation evidence for lateral excitation transfer in a self-assembled quantum-dot array

H. T. Johnson, R. Bose, H. D. Robinson, and B. B. Goldberg

Appl. Phys. Lett. 82, 3382 (2003); http://dx.doi.org/10.1063/1.1575509 (3 pages) | Cited 4 times

Online Publication Date: 12 May 2003

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Simulations of InAlAs/AlGaAs self-assembled quantum-dot arrays containing as many as 30 individual dots are used to identify a mechanism for lateral excitation transfer through partially delocalized heavy-hole states. Individual hole states exhibit wave-function splitting between several dots in the array, as well as partial confinement in the wetting layer, and have strong overlap with multiple conduction-band electron states in different quantum dots. Electron–hole pair energies involving these partially delocalized hole states correspond well with narrow resonances seen in the experimental photoluminescence excitation spectra taken for similar quantum-dot arrays using low-temperature near-field scanning optical microscopy. © 2003 American Institute of Physics.
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73.21.La Quantum dots
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots

Fine-tuning photorefractive properties of monolithic molecular materials

Zhanjia Hou, Wei You, and Luping Yu

Appl. Phys. Lett. 82, 3385 (2003); http://dx.doi.org/10.1063/1.1575938 (3 pages) | Cited 5 times

Online Publication Date: 12 May 2003

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Single component photorefractive materials based on small molecules have been synthesized. The sidechains located in the electron-withdrawing group of these molecules were systematically changed in order to investigate their influence. It was demonstrated that the photorefractive performance of these materials could be fine-tuned by changing the length of the sidechain. Excellent optical quality and photorefractive properties were obtained. A large net optical gain of 280 cm−1 at a low external field (38.3 V/μm) and a diffraction efficiency of 82% were observed at 780 nm. The results indicate that an optimum sidechain length exists for this type of molecules. © 2003 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Efficient frequency doubling of a femtosecond pulse with simultaneous group-velocity matching and quasi phase matching in periodically poled, MgO-doped lithium niobate

Nan Ei Yu, Sunao Kurimura, Kenji Kitamura, Jung Hoon Ro, Myoungsik Cha, Satoshi Ashihara, Tsutomu Shimura, Kazuo Kuroda, and Takunori Taira

Appl. Phys. Lett. 82, 3388 (2003); http://dx.doi.org/10.1063/1.1576296 (3 pages) | Cited 15 times

Online Publication Date: 12 May 2003

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We demonstrate efficient frequency doubling of 95-fs pulses with a small temporal broadening in a 10-mm-long, periodically poled, 5-mol % MgO-doped lithium niobate crystal. Simultaneous group-velocity matching and quasi phase matching were achieved by the off-diagonal nonlinear optical coefficient d32 at telecommunications range. © 2003 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

A hybrid laser system consisting of a frequency-doubled, narrow-line-width, distributed-feedback dye laser oscillator and a high saturation-fluence Ce:LiCaAlF6 crystal amplifier

D. Q. Hoa, N. D. Hung, J. Moroe, N. Takeyasu, and T. Imasaka

Appl. Phys. Lett. 82, 3391 (2003); http://dx.doi.org/10.1063/1.1576294 (3 pages) | Cited 2 times

Online Publication Date: 12 May 2003

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A tunable narrow-band picosecond dye laser emitting in the ultraviolet region was amplified using a Ce:LiCaAlF6 crystal pumped by the fourth-harmonic emission of a Nd:Y3Al5O12 laser. The single-pass gain obtained exceeded 2 in the spectral range of 288 to 297 nm. © 2003 American Institute of Physics.
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42.55.Mv Dye lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Ultrafast photoinduced anisotropy and optical switching in azobenzene sidechain polymers

Hui Wang, Yaping Huang, Zhigang Liu, Fuli Zhao, Weizhu Lin, Jian Wang, and Zhaoxi Liang

Appl. Phys. Lett. 82, 3394 (2003); http://dx.doi.org/10.1063/1.1576504 (3 pages) | Cited 11 times

Online Publication Date: 12 May 2003

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Photoinduced anisotropic and optical switching properties have been studied in two kinds of azobenzene sidechain polymers, a disazobenzene sidechain polymer (DAP–PGMA) and a monoazobenzene sidechain polymer P(MMA–co–MAZ). Picosecond optical switching dynamics have been observed in both DAP–PGMA and P(MMA–co–MAZ) films. The rise time of the optical switching in DAP–PGMA film is about 40 ps, which is much faster than that of P(MMA–co–MAZ) film (∼100 ps). DAP–PGMA shows enhanced photoanisotropy and larger birefringence ( ∼ 7.04×10−4) than that of P(MMA–co–MAZ) ( ∼ 1.34×10−4). The influence of the azobenzene sidechain groups on the photoanisotropic dynamics is discussed. © 2003 American Institute of Physics.
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42.70.Jk Polymers and organics
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
78.20.Fm Birefringence

Very high average power at room temperature from λ ≈ 5.9-μm quantum-cascade lasers

J. S. Yu, S. Slivken, A. Evans, J. David, and M. Razeghi

Appl. Phys. Lett. 82, 3397 (2003); http://dx.doi.org/10.1063/1.1574404 (3 pages) | Cited 23 times

Online Publication Date: 12 May 2003

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We report a very high average output power at room temperature for quantum-cascade lasers emitting at λ ≈ 5.9 μm. For high-reflectivity-coated 2-mm-long cavities, a low threshold current density of 1.7 kA/cm2 was obtained at room temperature. From 300 to 400 K, the characteristic temperature (T0) was 198 K. A maximum average output power of 0.67 W was achieved. In addition, 0.56 W average output power was observed at a duty cycle of 56%. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Effect of nitrogen fraction on the temperature dependence of GaNAs/GaAs quantum-well emission

R. J. Potter, N. Balkan, H. Carrère, A. Arnoult, E. Bedel, and X. Marie

Appl. Phys. Lett. 82, 3400 (2003); http://dx.doi.org/10.1063/1.1576511 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2003

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The effects of nitrogen fraction on the temperature dependence of GaNxAs1−x/GaAs (x<2.8%) quantum-well emission was investigated using steady-state photoluminescence between 2 and 300 K. At low temperatures, a characteristic S-shape behavior indicative of carrier localization was observed for each of the samples. This is believed to result from the large miscibility gap induced by the nitrogen, which results in structural/compositional fluctuations in the well. In the high temperature regime (T>150 K) where the emission has a linear dependence, a strong reduction in emission temperature dependence was observed with increasing nitrogen. The temperature dependence was modeled using the band anticrossing approach, with the interaction matrix element parameter CNM (VMN = −CMNmath) and the nitrogen level parameter γ (EN = EN0−γx) used as fitting parameters. © 2003 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells

Improved temperature characteristics of laser diodes with nonidentical multiple quantum wells due to temperature-induced carrier redistribution

Ching-Fuh Lin, Yi-Shin Su, Di-Ku Yu, Chao-Hsin Wu, and Bing-Ruey Wu

Appl. Phys. Lett. 82, 3403 (2003); http://dx.doi.org/10.1063/1.1577384 (3 pages) | Cited 5 times

Online Publication Date: 12 May 2003

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Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
73.20.At Surface states, band structure, electron density of states

Analysis of thermal stress in wafer bonding of dissimilar materials for the introduction of an InP-based light emitter into a GaAs-based three-dimensional photonic crystal

Shinpei Ogawa, Masahiro Imada, and Susumu Noda

Appl. Phys. Lett. 82, 3406 (2003); http://dx.doi.org/10.1063/1.1576911 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2003

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Thermal stresses generated by differences in the thermal expansion coefficients of InP and GaAs are analyzed in an attempt to introduce an InP-based light emitter into GaAs-based three-dimensional photonic crystal. Observations of the GaAs/InGaAsP bonding interface by scanning acoustic microscopy reveal that debonding occurs at approximately 300 °C due to thermal stress. Calculations of thermal stress by a two-dimensional finite element method suggested that thermal stress could be reduced by thinning the substrate, which was confirmed experimentally. Using these results, a three-dimensional photonic crystal with light emitter was successfully fabricated. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
02.70.Dh Finite-element and Galerkin methods
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Room-temperature operation of an InAs–GaAs–AlAs quantum-cascade laser

D. A. Carder, L. R. Wilson, R. P. Green, J. W. Cockburn, M. Hopkinson, M. J. Steer, R. Airey, and G. Hill

Appl. Phys. Lett. 82, 3409 (2003); http://dx.doi.org/10.1063/1.1576908 (3 pages) | Cited 14 times

Online Publication Date: 12 May 2003

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We report the shortest-wavelength (λ∼8.5 μm) room-temperature laser operation so far achieved for GaAs-based quantum-cascade (QC) lasers. By depositing InAs monolayers in the device active regions during growth, we are able to both reduce the emission wavelength and minimize thermally activated carrier leakage into quasicontinuum states. This approach results in laser operation up to 305 K, with a peak optical power of ∼10 mW at room temperature. A reduced temperature sensitivity of the threshold current compared with similar GaAs–Al0.45Ga0.55As QC lasers is also observed. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
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Reversible and bistable terahertz radiation from magnetoresistive Pr0.7Ca0.3MnO3 thin films

Noriaki Kida and Masayoshi Tonouchi

Appl. Phys. Lett. 82, 3412 (2003); http://dx.doi.org/10.1063/1.1575507 (3 pages) | Cited 4 times

Online Publication Date: 12 May 2003

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Reversible and bistable terahertz (THz) radiation by sweeping the temperature has been observed in a dipole-type photoswitching device fabricated on magnetoresistive charge-ordered manganite Pr0.7Ca0.3MnO3 thin film. Based on simultaneous measurements of the photocurrent, we show that this THz functionality of Pr0.7Ca0.3MnO3 arises from the instability of metallic patches embedded with a charge-ordered insulating phase, which is created by the illumination of visible light under an electric field at constant temperature, and that it can also be controlled by a subsequent change of temperature. © 2003 American Institute of Physics.
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75.47.Lx Magnetic oxides
73.50.Mx High-frequency effects; plasma effects
73.50.Pz Photoconduction and photovoltaic effects
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
75.47.Gk Colossal magnetoresistance
75.70.Ak Magnetic properties of monolayers and thin films
07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
78.70.Gq Microwave and radio-frequency interactions
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Strong in-plane polarized intraband absorption in vertically aligned InGaAs/GaAs quantum dots

A. M. Adawi, E. A. Zibik, L. R. Wilson, A. Lemaître, J. W. Cockburn, M. S. Skolnick, M. Hopkinson, G. Hill, S. L. Liew, and A. G. Cullis

Appl. Phys. Lett. 82, 3415 (2003); http://dx.doi.org/10.1063/1.1575931 (3 pages) | Cited 16 times

Online Publication Date: 12 May 2003

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We present a midinfrared absorption study of an n–i–n structure containing two planes of strongly coupled In0.5Ga0.5As self-assembled quantum dots. We find that the dominant absorption occurs for light polarized in the growth plane (E//xy), contrasting with uncoupled dots which exhibit stronger absorption for light polarized in the growth direction (E//z) in the same energy range. Results from the coupled dot sample indicate that the confinement length in the growth direction is increased, lowering the energy of the s-like ground state and hybridizing px,y-like excited states and wetting layer states. A significantly increased normal incidence photocurrent signal is measured for the sample containing coupled dots, relative to samples containing up to 30 layers of uncoupled dots, confirming the enhancement of the normal incidence absorption. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.30.Fs III-V and II-VI semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Midinfrared intersubband absorption in strain-compensated InGaP/InGaAs superlattices on (001) GaAs

M. P. Semtsiv, G. G. Tarasov, W. T. Masselink, H. Kissel, and M. Woerner

Appl. Phys. Lett. 82, 3418 (2003); http://dx.doi.org/10.1063/1.1573368 (3 pages) | Cited 1 time

Online Publication Date: 12 May 2003

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Intersubband optical transitions in strain-compensated In0.32Ga0.68As–In0.32Ga0.68P superlattices grown using gas-source molecular-beam epitaxy on (001)GaAs are investigated by means of midinfrared absorption and low-temperature photoluminescence. Strong absorption corresponding to the transition from the first to second electronic subband is measured at wavelengths between 5.6 and 10.5 μm. The data indicate that the conduction band offset between the strained In0.32Ga0.68As and the strained In0.32Ga0.68P is 370 meV and the electron effective mass in the strained In0.32Ga0.68As well is 0.060m0. This material system is an interesting GaAs-based candidate for applications in midinfrared intersubband emitters and detectors. © 2003 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
73.21.Cd Superlattices
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

A method to extract quantitative information in analyzer-based x-ray phase contrast imaging

E. Pagot, P. Cloetens, S. Fiedler, A. Bravin, P. Coan, J. Baruchel, J. Härtwig, and W. Thomlinson

Appl. Phys. Lett. 82, 3421 (2003); http://dx.doi.org/10.1063/1.1575508 (3 pages) | Cited 54 times

Online Publication Date: 12 May 2003

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Analyzer-based imaging is a powerful phase-sensitive technique that generates improved contrast compared to standard absorption radiography. Combining numerically two images taken on either side at ±1/2 of the full width at half-maximum (FWHM) of the rocking curve provides images of “pure refraction” and of “apparent absorption.” In this study, a similar approach is made by combining symmetrical images with respect to the peak of the analyzer rocking curve but at general positions, ±α⋅FWHM. These two approaches do not consider the ultrasmall angle scattering produced by the object independently, which can lead to inconsistent results. An accurate way to separately retrieve the quantitative information intrinsic to the object is proposed. It is based on a statistical analysis of the local rocking curve, and allows one to overcome the problems encountered using the previous approaches. © 2003 American Institute of Physics.
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07.85.-m X- and γ-ray instruments
78.70.Ck X-ray scattering
61.05.cf X-ray scattering (including small-angle scattering)

Compositionally-tuned epitaxial cubic MgxZn1−xO on Si(100) for deep ultraviolet photodetectors

W. Yang, S. S. Hullavarad, B. Nagaraj, I. Takeuchi, R. P. Sharma, T. Venkatesan, R. D. Vispute, and H. Shen

Appl. Phys. Lett. 82, 3424 (2003); http://dx.doi.org/10.1063/1.1576309 (3 pages) | Cited 65 times

Online Publication Date: 12 May 2003

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We report on the epitaxial growth of wide-band-gap cubic-phase MgxZn1−xO thin films on Si(100) by pulsed-laser deposition and fabrication of oxide-semiconductor-based ultraviolet photodetectors. The challenges of large lattice and thermal expansion mismatch between Si and MgxZn1−xO have been overcome by using a thin SrTiO3 buffer layer. The heteroepitaxy of cubic-phase MgxZn1−xO on Si was established with epitaxial relationship of MgxZn1−xO(100)//SrTiO3(100)//Si(100) and MgxZn1−xO[100]//SrTiO3[100]//Si[110]. The minimum yield of the Rutherford backscattering ion channeling in MgxZn1−xO layer was only 4%, indicating good crystalline quality of the film. Smooth surface morphology with rms roughness of 0.6 nm was observed using atomic force microscopy. Photodetectors fabricated on Mg0.68Zn0.32O/SrTiO3/Si show peak photoresponse at 225 nm, which is in the deep UV region. © 2003 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
81.05.Dz II-VI semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
68.60.Dv Thermal stability; thermal effects

Impact of stress on oxygen vacancy ordering in epitaxial (La0.5Sr0.5)CoO3−∂ thin films

Dmitri O. Klenov, Wolfgang Donner, Brendan Foran, and Susanne Stemmer

Appl. Phys. Lett. 82, 3427 (2003); http://dx.doi.org/10.1063/1.1575503 (3 pages) | Cited 17 times

Online Publication Date: 12 May 2003

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We investigate oxygen vacancy ordering in epitaxial (La0.5Sr0.5)CoO3−∂ thin films grown by sputter deposition on (001) LaAlO3 and (001) SrTiO3. After annealing at 500 °C under oxygen partial pressures greater than those used during deposition, films transform to a long-range oxygen vacancy ordered structure with orthorhombic symmetry. Observed orientation variants of the oxygen vacancy ordered structures are different for the two substrates. We discuss the relationship between film stress due to lattice and thermal mismatch with the substrate, and vacancy ordering. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
81.15.Cd Deposition by sputtering

In situ photoemission characterization of terminating-layer-controlled La0.6Sr0.4MnO3 thin films

H. Kumigashira, K. Horiba, H. Ohguchi, K. Ono, M. Oshima, N. Nakagawa, M. Lippmaa, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 82, 3430 (2003); http://dx.doi.org/10.1063/1.1575932 (3 pages) | Cited 29 times

Online Publication Date: 12 May 2003

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We report on the fabrication of terminating-layer-controlled La0.6Sr0.4MnO3 (LSMO) thin films and in situ characterization of the films using photoemission spectroscopy. The terminating layer of the LSMO films was changed from B to A site by inserting one atomic layer of SrO between the LSMO film and a TiO2-terminated SrTiO3(001) substrate. The successful control of the terminating layer was confirmed by measuring the angular dependence of core-level spectra. Detailed analysis of the Sr 3d core levels revealed considerable differences in chemical bonding states of Sr atoms in the surface regions of films with different terminating layers. © 2003 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.20.At Surface states, band structure, electron density of states

Ga vacancies as dominant intrinsic acceptors in GaN grown by hydride vapor phase epitaxy

J. Oila, J. Kivioja, V. Ranki, K. Saarinen, D. C. Look, R. J. Molnar, S. S. Park, S. K. Lee, and J. Y. Han

Appl. Phys. Lett. 82, 3433 (2003); http://dx.doi.org/10.1063/1.1569414 (3 pages) | Cited 49 times

Online Publication Date: 12 May 2003

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Positron annihilation measurements show that negative Ga vacancies are the dominant acceptors in n-type gallium nitride grown by hydride vapor phase epitaxy. The concentration of Ga vacancies decreases, from more than 1019 to below 1016 cm−3, as the distance from the interface region increases from 1 to 300 μm. These concentrations are the same as the total acceptor densities determined in Hall experiments. The depth profile of O is similar to that of VGa, suggesting that the Ga vacancies are complexed with the oxygen impurities. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.70.Bj Positron annihilation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
81.05.Ea III-V semiconductors

Er3+ photoluminescence from Er-doped amorphous SiOx films prepared by pulsed laser deposition at room temperature: The effects of oxygen concentration

Jeong Sook Ha, Chang Hyun Bae, Sang Hwan Nam, Seung Min Park, Young Rae Jang, Keon Ho Yoo, and Kyoungwan Park

Appl. Phys. Lett. 82, 3436 (2003); http://dx.doi.org/10.1063/1.1573335 (3 pages) | Cited 13 times

Online Publication Date: 12 May 2003

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We have fabricated Er-doped amorphous SiOx films by laser ablation of a Si:Er2O3 target in He atmosphere. The photoluminescence intensity at 1.54 μm was highly dependent on the oxygen content in the film, which turned out to be changed significantly by the ambient He pressure. Also, we have adopted time-of-flight quadrupole mass spectroscopy to obtain kinetic energies of ionic species in a plume produced by laser ablation. Si and Er ions do not overlap spatially as they expand toward the Si substrate and Er ions impinge on the preformed SiOx layer. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
82.80.Rt Time of flight mass spectrometry

Nonlithographic epitaxial SnxGe1−x dense nanowire arrays grown on Ge(001)

Regina Ragan, Channing C. Ahn, and Harry A. Atwater

Appl. Phys. Lett. 82, 3439 (2003); http://dx.doi.org/10.1063/1.1563834 (3 pages) | Cited 8 times

Online Publication Date: 12 May 2003

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We have grown 1-μm-thick SnxGe1−x/Ge(001) epitaxial films with 0<x<0.085 by molecular-beam epitaxy. These films evolve during growth into a dense array of SnxGe1−x nanowires oriented along [001], as confirmed by composition contrast observed in scanning transmission electron microscopy in planar view. The Sn-rich regions in these films dominate optical absorption at low energy; phase-separated SnxGe1−x alloys have a lower-energy band gap than homogeneous alloys with the same average Sn composition. © 2003 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.30.Hv Other nonmetallic inorganics

Effect of Al2O3 capping layer on suppression of interfacial SiO2 growth in HfO2/ultrathin SiO2/Si(001) structure

Manisha Kundu, Noriyuki Miyata, Toshihide Nabatame, Tsuyoshi Horikawa, Masakazu Ichikawa, and Akira Toriumi

Appl. Phys. Lett. 82, 3442 (2003); http://dx.doi.org/10.1063/1.1576293 (3 pages) | Cited 17 times

Online Publication Date: 12 May 2003

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We investigated the effect a 1.2-nm-thick Al2O3 capping layer had on suppressing interfacial Si oxidation in a 2.6-nm-HfO2/0.35-nm-SiO2/Si(001) structure during postdeposition annealing in an oxygen ambient. An incubation period (IP) was initially observed during which the HfO2/Si interface exhibited remarkable stability without any interfacial SiO2 growth. This was then followed by very slow interface oxidation. Our detailed study suggested that low oxidant diffusion through the capping layer determined the effective IP. Furthermore, HfO2/Si interface oxidation, which proceeded through a two-step process that was similar to an uncapped structure, was severely constrained by the limited availability of oxygen at the Al2O3/HfO2 interface. © 2003 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Erbium–thulium interaction in broadband infrared luminescent silicon-rich silicon oxide

Se-Young Seo, Jung H. Shin, Byeong-Soo Bae, Namkyoo Park, J. J. Penninkhof, and A. Polman

Appl. Phys. Lett. 82, 3445 (2003); http://dx.doi.org/10.1063/1.1577217 (3 pages) | Cited 16 times

Online Publication Date: 12 May 2003

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The Er–Tm interaction and its effect on the luminescence from Er–Tm codoped silicon-rich silicon oxide (SRSO) is investigated. Er and Tm ions were implanted into SRSO films, which consist of Si nanocrystals embedded in a SiO2 matrix. A broad luminescence spectrum extending from 1.5 to 2.0 μm was observed under excitation with a single light source due to the simultaneous, nonresonant excitation of both Er3+ and Tm3+ via Si nanocrystals. The absolute Er3+ luminescence intensity, however, is reduced relative to the case without Tm codoping. Comparison of the Er3+ and Tm3+ luminescence intensities, lifetimes, and their pump power dependence suggest that Er–Tm interaction leading to an energy transfer from the Er3+:4I13/2 state to the excited Tm3+:3H4 state is responsible for the reduction in the Er luminescence intensity. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Optical properties of the isoelectronic trap Hg in ZnO

Th. Agne, M. Dietrich, J. Hamann, S. Lany, H. Wolf, and Th. Wichert

Appl. Phys. Lett. 82, 3448 (2003); http://dx.doi.org/10.1063/1.1576912 (3 pages) | Cited 4 times

Online Publication Date: 12 May 2003

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Nominally undoped ZnO crystals were doped with Hg by implanting radioactive 197Hg/197Au atoms. After annealing at 1073 K, the photoluminescence (PL) spectra recorded at 1.6 K exhibit a Hg related band in the region between 3.28 and 2.85 eV. The sharp no-phonon line, which is observed at 3.276 51 eV, is assigned to a bound exciton. At lower energies, a phonon sideband is visible, which is caused by the strong coupling with acoustical and optical phonons. It is shown that these PL signals are caused by an exciton bound to a Hg atom that resides on a cation site. © 2003 American Institute of Physics.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
63.20.kk Phonon interactions with other quasiparticles

Interplay between the growth temperature, microstructure, and optical properties of GaInNAs quantum wells

J.-M. Chauveau, A. Trampert, K. H. Ploog, M.-A. Pinault, and E. Tournié

Appl. Phys. Lett. 82, 3451 (2003); http://dx.doi.org/10.1063/1.1577393 (3 pages) | Cited 24 times

Online Publication Date: 12 May 2003

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We investigated the influence of the growth temperature (Tgr) on the microstructure and on the optical properties of GaInNAs quantum wells (QWs). By comparing the structural information (transmission electron microscopy) with the optical properties (photoluminescence spectroscopy), we demonstrate that high photoluminescence efficiency of GaInNAs QWs is achieved only when the two-dimensional growth mode is preserved, which can be obtained at a low Tgr even for high In content. We also show composition modulations in the GaInNAs QWs, which can lead to the interface roughness. © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
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