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9 Jul 2007

Volume 91, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 023101 (2007); http://dx.doi.org/10.1063/1.2755879 (3 pages)

M. Fendrich and T. Kunstmann
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Temperature induced stress phase transition in CdTe quantum dots observed by dielectric constant and thermal diffusivity measurements

S. G. C. Moreira, E. C. da Silva, A. M. Mansanares, L. C. Barbosa, and C. L. Cesar

Appl. Phys. Lett. 91, 021101 (2007); http://dx.doi.org/10.1063/1.2751128 (3 pages) | Cited 3 times

Online Publication Date: 9 July 2007

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The authors measured the dielectric constant by capacitance method and the thermal diffusivity by thermal lens technique in the temperature range from 20 to 300 K for CdTe quantum dot doped borosilicate glass samples. Results show a huge difference between the thermal behavior of the pure glass matrix, without quantum dots, and of the doped glass, especially around 90 and 250 K. The authors attributed this difference to the phase transition experienced by the CdTe nanocrystals due to the high pressure exerted by the glass matrix over the CdTe quantum dots. The temperature induced stress is caused by the thermal expansion coefficient mismatch between the quantum dot and the glass matrix.
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64.70.K- Solid-solid transitions
68.65.Hb Quantum dots (patterned in quantum wells)
62.50.-p High-pressure effects in solids and liquids
77.22.Ch Permittivity (dielectric function)
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems

Optical transitions in type-II InAs/GaAs quantum dots covered by a GaAsSb strain-reducing layer

C. Y. Jin, H. Y. Liu, S. Y. Zhang, Q. Jiang, S. L. Liew, M. Hopkinson, T. J. Badcock, E. Nabavi, and D. J. Mowbray

Appl. Phys. Lett. 91, 021102 (2007); http://dx.doi.org/10.1063/1.2752778 (3 pages) | Cited 29 times

Online Publication Date: 9 July 2007

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The excitation power dependence of the ground and excited state transitions in type-II InAs-GaAs0.78Sb0.22 quantum dot structure has been studied. Both transitions exhibit a strong blueshift with increasing excitation power but their separation remains constant. This behavior indicates a carrier-induced electric field oriented predominantly along the growth axis, which requires the holes to be localized in the GaAsSb above quantum dots. An accelerated blueshift of the ground state emission is observed once the excited state in the dots starts to populate. This behavior can be explained by a smaller spontaneous recombination coefficient for the excited state transition.
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78.67.Hc Quantum dots
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Plasmonic very-small-aperture lasers

Baoshan Guo, Guofeng Song, and Lianghui Chen

Appl. Phys. Lett. 91, 021103 (2007); http://dx.doi.org/10.1063/1.2755784 (3 pages) | Cited 12 times

Online Publication Date: 9 July 2007

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The fabrication of plasmonic very-small-aperture lasers is demonstrated in this letter. It is an integration of the surface plasmon structures and very-small-aperture lasers (VSAL). The experimental and numerical results demonstrate that the transmission field can be confined to a spot with subwavelength width in the far field, and the power output can be enhanced 140% of the normal VSAL. Such a device can be useful in the application of a high resolution far-field scanning optical microscope.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.82.Gw Other integrated-optical elements and systems

Laser oscillations of whispering gallery modes in thiophene/phenylene co-oligomer microrings

Seiji Fujiwara, Kazuki Bando, Yasuaki Masumoto, Fumio Sasaki, Shunsuke Kobayashi, Satoshi Haraichi, and Shu Hotta

Appl. Phys. Lett. 91, 021104 (2007); http://dx.doi.org/10.1063/1.2755925 (3 pages) | Cited 11 times

Online Publication Date: 9 July 2007

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Laser oscillation of whispering gallery modes was observed in microring structures of semiconducting thiophene/phenylene co-oligomer (TPCO) crystals at room temperature. Microring structures were formed by dry etching from thin film crystals of TPCO. The thresholds for the laser oscillation of a microring and a thin film crystal are 200 and 1400 μJ/cm2 for picosecond excitation, respectively. Therefore, the threshold for the microring was reduced to 1/7 of that for the thin film crystal. The dramatic reduction of threshold clearly demonstrates the importance of microcavity in making efficient organic semiconductor lasers.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Sa Microcavity and microdisk lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Electrophotoluminescence of ZnO film

Xiangyang Ma, Peiliang Chen, Dongsheng Li, Yuanyuan Zhang, and Deren Yang

Appl. Phys. Lett. 91, 021105 (2007); http://dx.doi.org/10.1063/1.2753760 (3 pages) | Cited 18 times

Online Publication Date: 10 July 2007

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The electric-field-controlled photoluminescence (PL), i.e., electrophotoluminescence (EPL) of ZnO film has been investigated via a ZnO-based metal-insulator-semiconductor (MIS) structure on a silicon substrate applied with different biases. Compared with the PL of ZnO film in the case where there is no bias on the MIS structure, the positive bias with negative voltage applied on silicon substrate significantly enhances the near-band-edge ultraviolet emission while suppressing the deep-level-related visible emissions, whereas the negative bias hardly changes the PL of ZnO film. The mechanism for EPL of ZnO film is proposed in terms of the electric-field effect on the bending of energy bands of ZnO.
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78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors

Near-infrared photoluminescence of erbium tris(8-hydroxyquinoline) spin-coated thin films induced by low coherence light sources

S. Penna, A. Reale, R. Pizzoferrato, G. M. Tosi Beleffi, D. Musella, and W. P. Gillin

Appl. Phys. Lett. 91, 021106 (2007); http://dx.doi.org/10.1063/1.2755933 (3 pages) | Cited 3 times

Online Publication Date: 10 July 2007

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The authors present the characterization of spin-coated erbium tris(8-hydroxyquinoline) (ErQ3) solution on glass substrates under high temperature conditions. Absorption and infrared photoluminescence, induced by laser and light emitting diode sources, were measured and compared to cast and evaporated ErQ3 samples. A broad absorption band and 1.52 μm luminescence were observed, suggesting spin coating as a valid deposition technique for processing of organic infrared emitting diodes.
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78.55.Kz Solid organic materials
78.30.Jw Organic compounds, polymers
78.66.Qn Polymers; organic compounds

Germanium near infrared detector in silicon on insulator

L. Colace, V. Sorianello, M. Balbi, and G. Assanto

Appl. Phys. Lett. 91, 021107 (2007); http://dx.doi.org/10.1063/1.2757123 (3 pages) | Cited 5 times

Online Publication Date: 11 July 2007

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The authors demonstrate near infrared photodetectors in evaporated germanium on silicon-on-insulator waveguides. The authors achieve peak responsivities as high as 1 A/W and dark current densities as low as 40 nA at a reverse bias of 1 V. Owing to the low deposition temperature, this technology allows for simple and low cost monolithic integration with silicon.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Demonstrations of the diffraction and dispersion phenomena of part Fresnel phase zone plates

Binzhi Zhang, Daomu Zhao, and Shaomin Wang

Appl. Phys. Lett. 91, 021108 (2007); http://dx.doi.org/10.1063/1.2757126 (3 pages) | Cited 4 times

Online Publication Date: 11 July 2007

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The authors report on experimental demonstrations of the diffraction and dispersion phenomena of part Fresnel phase zone plates (FPZPs) by employing a He–Ne laser beam and a white point source. The experimental results have shown that a part square FPZP can behave like a complete circular FPZP, and a part circular FPZP has a focus at 1/3 f and f with a shift. Some numerical simulations are performed. The simulations and the experiments have shown that the diffraction and dispersion properties of part FPZPs can be well explained by the different diffraction orders.
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42.79.Ci Filters, zone plates, and polarizers
42.87.-d Optical testing techniques

Metal and dielectric duality for an aligned Al nanorod array

Yi-Jun Jen and Ching-Wei Yu

Appl. Phys. Lett. 91, 021109 (2007); http://dx.doi.org/10.1063/1.2757133 (3 pages) | Cited 1 time

Online Publication Date: 11 July 2007

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In this letter, aluminum (Al) is used to make a narrow rod array (NRA) by oblique angle deposition method. The Al NRA film exhibits both metallic and dielectric optical characteristics. Like metal films, the Al NRA film only weakly disperses visible wavelength of normally incident light. However, strong interference causes the obliquely incident s-polarized and p-polarized lights to resonate in the Al NRA film. Even though the optical constant of the Al NRA film is dielectriclike, the surface plasmon wave excited and propagating on the surface of Al NRA is demonstrated to be responsible for the p-polarized resonance.
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78.66.Bz Metals and metallic alloys
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
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)

Single point defect photonic crystal nanocavity with ultrahigh quality factor achieved by using hexapole mode

Takasumi Tanabe, Akihiko Shinya, Eiichi Kuramochi, Shingo Kondo, Hideaki Taniyama, and Masaya Notomi

Appl. Phys. Lett. 91, 021110 (2007); http://dx.doi.org/10.1063/1.2757099 (3 pages) | Cited 15 times

Online Publication Date: 11 July 2007

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Photonic crystal (PhC) nanocavities with an extremely high quality factor (Q) based on a point defect are fabricated and their properties are studied. Their confinement of light is based on rotational symmetry, which forms a hexapole mode with a Q of 3.2×105. It demonstrates that this nanocavity is an alternative candidate for achieving an ultrahigh Q. In addition, we observed bistable behavior based on the thermo-optic effect at a threshold power of a few 100 μW. We also investigated the dynamic properties of this cavity, where we observed that the cavity exhibits a smaller Q at a higher input power.
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42.82.Gw Other integrated-optical elements and systems
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Dispersion of silicon nonlinearities in the near infrared region

Q. Lin, J. Zhang, G. Piredda, R. W. Boyd, P. M. Fauchet, and G. P. Agrawal

Appl. Phys. Lett. 91, 021111 (2007); http://dx.doi.org/10.1063/1.2750523 (3 pages) | Cited 43 times

Online Publication Date: 12 July 2007

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The authors present the detailed characterization of the wavelength dependence of two-photon absorption and the Kerr nonlinearity in silicon over a spectral range extending from 1.2 to 2.4 μm. They show that silicon exhibits a significant increase in its nonlinear figure of merit with increasing wavelengths beyond the two telecommunication bands. They expect their results to provide guidance for extending nonlinear silicon photonics into new spectral regimes.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Db Elemental semiconductors and insulators

Tunable surface plasmon mediated emission from semiconductors by using metal alloys

D. Y. Lei, J. Li, and H. C. Ong

Appl. Phys. Lett. 91, 021112 (2007); http://dx.doi.org/10.1063/1.2752770 (3 pages) | Cited 19 times

Online Publication Date: 12 July 2007

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The authors have explored the possibility of using binary metal alloys on surface plasmon mediated emission from semiconductor. By adjusting the alloy composition, they have found that the surface plasmon resonance energy can be tuned to match with the emission energy of semiconductor so that the energy transfer process between the semiconductor and surface plasmons can be optimized. They have calculated the plasmonic density of states and Purcell factor for ZnO and ZnTe at different alloy compositions and the results support the argument. Experimentally, they have prepared AlxAg1−x/ZnO films at different compositions and have measured their photoluminescence. The band-edge emission from Al0.8Ag0.2/ZnO is found to be ∼ 60 times stronger than that of bare ZnO, which is consistent with the theoretical prediction. As a result, metal alloys can be considered as a simple and effective means in optimizing the surface plasmon mediated emission.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.-w Optical properties of specific thin films
78.55.-m Photoluminescence, properties and materials

Direct measurement of increased light intensity in optical waveguides coupled to a surface plasmon spectroscopy setup

M. Dürr, B. Menges, W. Knoll, A. Yasuda, and G. Nelles

Appl. Phys. Lett. 91, 021113 (2007); http://dx.doi.org/10.1063/1.2753757 (3 pages) | Cited 5 times

Online Publication Date: 13 July 2007

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The local increase of light intensity in waveguide structures was monitored by a combination of conventional surface plasmon spectroscopy and a dye-sensitized solar cell (DSSC). The sensitized nanoporous TiO2 layer of the DSSC served both as waveguide structure and light absorber in the DSSC. If the conditions for the excitation of guided modes in the TiO2 waveguide structure were fulfilled, increased light intensity in the porous layer was monitored by an increase of short circuit current in the DSSC. Comparison with direct illumination yields an increase of intensity by a factor of 19±6, in good agreement with transfer matrix calculations.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Defect reduction of GaAs epitaxy on Si (001) using selective aspect ratio trapping

J. Z. Li, J. Bai, J.-S. Park, B. Adekore, K. Fox, M. Carroll, A. Lochtefeld, and Z. Shellenbarger

Appl. Phys. Lett. 91, 021114 (2007); http://dx.doi.org/10.1063/1.2756165 (3 pages) | Cited 23 times

Online Publication Date: 13 July 2007

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Metal-organic chemical vapor deposition growth of GaAs on Si was studied using the selective aspect ratio trapping method. Vertical propagation of threading dislocations generated at the GaAs/Si interface was suppressed within an initial thin GaAs layer inside SiO2 trenches with aspect ratio >1, leading to defect-free GaAs regions up to 300 nm in width. Cross-sectional and plan-view transmission electron microscopies were used to characterize the defect reduction. Material quality was confirmed by room temperature photoluminescence measurements. This approach shows great promise for the fabrication of optoelectronic integrated circuits on Si substrates.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
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Nonlithographic fabrication of surface-enhanced Raman scattering substrates using a rastered atmospheric-pressure microplasma source

Wei-Hung Chiang, Matthew Cochey, R. Craig Virnelson, and R. Mohan Sankaran

Appl. Phys. Lett. 91, 021501 (2007); http://dx.doi.org/10.1063/1.2757152 (3 pages) | Cited 10 times

Online Publication Date: 13 July 2007

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A nonlithographic patterning technique based on a numerically controlled atmospheric-pressure microplasma source has been developed to fabricate surface-enhanced Raman scattering (SERS) substrates. Microstructures in silver (Ag) films on glass are created by localized physical sputtering of Ag atoms using an argon (Ar) microplasma horizontally scanned across the glass substrate. Detection of crystal violet on patterned substrates shows an enhancement of the Raman scattering signal intensity by eight to ten orders of magnitude higher than bare Ag/glass substrates. The SERS enhancement depends on the pattern geometry showing that the mechanism is related to surface irregularities in the sputtered holes.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
52.77.-j Plasma applications
68.55.-a Thin film structure and morphology
68.47.Gh Oxide surfaces
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Dynamic range of nanoresonators with random rough surfaces in the presence of thermomechanical and momentum exchange noise

G. Palasantzas

Appl. Phys. Lett. 91, 021901 (2007); http://dx.doi.org/10.1063/1.2751599 (3 pages) | Cited 5 times

Online Publication Date: 9 July 2007

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The authors investigate the simultaneous influence of thermomechanical and momentum exchange noise on the linear dynamic range DR of nanoresonators with random rough surfaces. The latter are characterized by the roughness amplitude w, the lateral correlation length ξ, and the roughness exponent 0<H<1. The dynamic range increases with increasing roughness (decreasing H and/or increasing roughness ratio w/ξ) if the quality factor due to gas collisions is smaller than the intrinsic quality factor associated with thermomechanical noise. The influence of the roughness ratio w/ξ on DR is significant for intermediate roughness exponents that are commonly observed in experiments.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
72.70.+m Noise processes and phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Ct Interface structure and roughness

Accommodation mechanism of InN nanocolumns grown on Si(111) substrates by molecular beam epitaxy

J. Grandal, M. A. Sánchez-García, E. Calleja, E. Luna, and A. Trampert

Appl. Phys. Lett. 91, 021902 (2007); http://dx.doi.org/10.1063/1.2756293 (3 pages) | Cited 14 times

Online Publication Date: 9 July 2007

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High quality InN nanocolumns have been grown by molecular beam epitaxy on bare and AlN-buffered Si(111) substrates. The accommodation mechanism of the InN nanocolumns to the substrate was studied by transmission electron microscopy. Samples grown on AlN-buffered Si(111) show abrupt interfaces between the nanocolumns and the buffer layer, where an array of periodically spaced misfit dislocations develops. Samples grown on bare Si(111) exhibit a thin SixNy at the InN nanocolumn/substrate interface because of Si nitridation. The SixNy thickness and roughness may affect the nanocolumn relative alignment to the substrate. In all cases, InN nanocolumns grow strain- and defect-free.
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81.05.Ea III-V semiconductors
81.07.Bc Nanocrystalline materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.-w Structure of nanoscale materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Spectral dependence of the photoluminescence decay in disordered semiconductors

O. Rubel, W. Stolz, and S. D. Baranovskii

Appl. Phys. Lett. 91, 021903 (2007); http://dx.doi.org/10.1063/1.2755927 (3 pages) | Cited 9 times

Online Publication Date: 9 July 2007

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Kinetics of the energy transfer and the corresponding photoluminescence decay at selected photon energies in disordered semiconductors are studied theoretically. The authors show a straightforward way to arrive analytically at the solutions for the spectral and time dependences of the photoluminescence decay within a model based on the interplay between the radiative recombination and hopping energy relaxation of localized excitons. The theory is supported by comparison with experimental data, which yields valuable information on major properties of disorder in the underlying structures.
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78.55.-m Photoluminescence, properties and materials
71.35.-y Excitons and related phenomena

Spectroscopic evidence for a surface layer in CuInSe2:Cu deficiency

Sung-Ho Han, Falah S. Hasoon, Allen M. Hermann, and Dean H. Levi

Appl. Phys. Lett. 91, 021904 (2007); http://dx.doi.org/10.1063/1.2755718 (3 pages) | Cited 7 times

Online Publication Date: 9 July 2007

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The near-surface region of thin-film polycrystalline (PX) CuIn1−xGaxSe2 (CIGS) is considered important because it is the region where the electrical junction forms in a CIGS photovoltaic device. Spectroscopic ellipsometry measurements of polycrystalline CuInSe2 films reveal that there is a thin layer at the surface which has different optical and electronic properties from those of the bulk film. This surface layer of thin-film CIGS has a larger band gap and greater spin-orbit interaction energy than the bulk film. These properties indicate that the surface layer is more Cu deficient than the bulk in the nearly stoichiometric thin-film PX-CIGS used in photovoltaic devices. This work provides an insight into the importance of surface layer engineering for photovoltaic device design.
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.At Surface states, band structure, electron density of states
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.20.Nr Semiconductor compounds

Volume conservation in bulk metallic glasses

D. Ma, A. D. Stoica, and X.-L. Wang

Appl. Phys. Lett. 91, 021905 (2007); http://dx.doi.org/10.1063/1.2751595 (3 pages) | Cited 8 times

Online Publication Date: 10 July 2007

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The authors report that the excess molar volumes of mixing for ∼ 30 metalloid-free bulk metallic glasses (BMGs) are essentially zero, indicating that the original volumes of “mechanically mixed” constituent elemental metals are conserved after glass formation. This is attributed to the lack of solute-solute bonds and the ideal-mixing nature of solvent-solute bonding upon amorphization. The hard-sphere atomic packing fractions of most of these BMGs are found to be ∼ 0.74, comparable to the maximum packing efficiency for close-packed structures. These findings present a different perspective for understanding amorphous structures.
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61.43.Fs Glasses
61.43.Dq Amorphous semiconductors, metals, and alloys

Early stage of material movements in eutectic SnPb solder joint undergoing current stressing at 150 °C

C. E. Ho, A. Lee, K. N. Subramanian, and W. Liu

Appl. Phys. Lett. 91, 021906 (2007); http://dx.doi.org/10.1063/1.2756292 (3 pages) | Cited 6 times

Online Publication Date: 10 July 2007

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X-ray fluorescence spectroscopy was used to study movements of Sn and Pb in the eutectic SnPb solder joint undergoing electromigration with a current density of 104 A/cm2 at 150 °C. During early stages of current stressing, Sn moves toward the anode faster than Pb. However, on continued application of current stressing, both Sn and Pb will continue to accumulate at the anode. Such accumulation of conductive species facilitates the formation of hillock with associated valley near the cathode.
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66.30.Qa Electromigration
78.70.En X-ray emission spectra and fluorescence

Correlation between icosahedral short range order, glass forming ability, and thermal stability of Zr–Ti–Ni–Cu–(Be) glasses

S. Mechler, G. Schumacher, I. Zizak, M.-P. Macht, and N. Wanderka

Appl. Phys. Lett. 91, 021907 (2007); http://dx.doi.org/10.1063/1.2755924 (3 pages) | Cited 10 times

Online Publication Date: 10 July 2007

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The structure and the crystallization behavior of the bulk metallic glass Zr46.8Ti8.2Ni10Cu7.5Be27.5 and of its Be-free derivative Zr64.5Ti11.4Ni13.8Cu10.3 are analyzed by means of differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. These alloys reveal different glass forming abilities. Thermal stability and crystallization behavior of the glasses are also different. These differences are correlated with the different degrees of icosahedral short range order in the glasses. Results fit to the model of geometric frustration, which describes the structure of metallic glasses as “highly defective quasicrystals.” In the present case Be degrades the ideal quasicrystalline structure.
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61.43.Fs Glasses
64.70.K- Solid-solid transitions

Pattern formation in martensitic thin films

Y. C. Shu and J. H. Yen

Appl. Phys. Lett. 91, 021908 (2007); http://dx.doi.org/10.1063/1.2756320 (3 pages) | Cited 11 times

Online Publication Date: 10 July 2007

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Pattern formation in martensitic materials refers to the accommodation problem of how to mix martensitic variants coherently to minimize the strain energy. A framework motivated by energy-minimizing multirank laminated patterns is proposed to study this problem in martensitic films. It is found that the interfaces between the variants of martensite can be quite different in thin films than in bulk materials, and they typically have a simpler structure. Various intriguing and fascinating self-accommodation patterns are predicted for martensitic thin films with different orientations. The results are in good agreement with the Bhattacharya-James thin-film theory [ K. Bhattacharya and R. D. James, J. Mech. Phys. Solids 47, 531 (1999) ] as well as with experimental observations.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
68.55.-a Thin film structure and morphology

Effect of ion-irradiation induced defects on the nanocluster Si/Er3+ coupling in Er-doped silicon-rich silicon oxide

Se-Young Seo, Hoon Jeong, Jung H. Shin, Han Woo Choi, Hyung Joo Woo, and Joon Kon Kim

Appl. Phys. Lett. 91, 021909 (2007); http://dx.doi.org/10.1063/1.2752538 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2007

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The effect of ion-irradiation induced defects on the nanocluster Si/Er3+ coupling in Er-doped silicon-rich silicon oxide (SRSO) thin film is investigated. Er-doped SRSO, which consists of silicon nanoclusters (nc-Si) in a SiO2 matrix, was fabricated using electron-cyclotron resonance plasma enhanced chemical vapor deposition using SiH4 and O2 with concurrent sputtering of Er followed by a high temperature annealing. Defects were introduced into the film via irradiation with 3 MeV Si ions and subsequently removed by high temperature annealings. The authors find that ion irradiation reduces Er3+ luminescence from SRSO films, even when the excitation cross section and luminescence efficiency of Er3+ ions are completely restored. On the other hand, ion irradiation increases the intrinsic nc-Si luminescence and has little effect on the Er3+ luminescence from a similarly prepared, Er-doped SiO2 film, indicating that the presence of irradiation induced defects in the initial amorphous film can reduce the number of Er3+ ions available for nc-Si mediated luminescence by as much as a factor of 3.
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78.55.Hx Other solid inorganic materials
78.55.Qr Amorphous materials; glasses and other disordered solids
78.66.Nk Insulators
61.80.Jh Ion radiation effects
61.82.Ms Insulators
81.40.Gh Other heat and thermomechanical treatments

Optical properties of (In,Ga)As capped InAs quantum dots grown on [11k] substrates

V. Mlinar and F. M. Peeters

Appl. Phys. Lett. 91, 021910 (2007); http://dx.doi.org/10.1063/1.2753745 (3 pages) | Cited 2 times

Online Publication Date: 11 July 2007

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Using three-dimensional k∙p calculation including strain and piezoelectricity, the authors showed that the size of the quantum dot (QD) in the growth direction determines the influence of the (In,Ga)As capping layer on the optical properties of [11k] grown InAs QDs, where k = 1,2,3. For flat dots, increase of In concentration in the capping layer leads to a decrease of the transition energy, whereas for large dots an increase of the In concentration in the capping layer is followed by an increase of the transition energy up to a critical concentration of In, after which the optical transition energy starts to decrease.
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78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
77.65.-j Piezoelectricity and electromechanical effects
61.72.S- Impurities in crystals
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