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2 Nov 1998

Volume 73, Issue 18, pp. 2543-2690

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Tunable wavelength filters with Bragg gratings in polymer waveguides

Min-Cheol Oh, Hyung-Jong Lee, Myung-Hyun Lee, Joo-Heon Ahn, Seon Gyu Han, and Hae-Guen Kim

Appl. Phys. Lett. 73, 2543 (1998); http://dx.doi.org/10.1063/1.122527 (3 pages) | Cited 34 times

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Tunable wavelength filters are demonstrated based on the thermo-optic refractive index change of the polymer waveguide with Bragg reflection grating. For the low-loss waveguide operating around 1.55 μm, fluorinated polymers are incorporated. Bragg reflection gratings are fabricated using a phase mask and a high-index polymer. The Bragg reflector exhibits a narrow bandwidth of less than 1.0 nm, a crosstalk of −20 dB, an insertion loss of 3.2 dB, and a flat-top passband. The peak wavelength of Bragg reflection is shifted over 11 nm with a slight insertion loss change. The thermo-optic tuning efficiency is 22 nm/W and the peak shift is linearly proportional to the heating power. © 1998 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Jk Polymers and organics
42.79.Dj Gratings
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects

Effect of a local electric field on photogeneration efficiency in a photorefractive polymer

Liming Wang, Qing Wang, and Luping Yu

Appl. Phys. Lett. 73, 2546 (1998); http://dx.doi.org/10.1063/1.122528 (3 pages) | Cited 2 times

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The effect of a local electric field upon photogeneration efficiency was investigated through analyses of the dependence of photocurrent, photorefractive gain, diffraction efficiency, and birefringence on the applied field of a novel photorefractive polymer containing an ionic tri(bispyridyl) ruthenium complex. It was found that since this polymer system possesses a low glass transition temperature, the dipole moments formed between the counter ions are readily aligned and generate ionic dipole field which screen photogeneration sites from the applied field. This local field lowers the photogeneration efficiency and results in the saturation of photocurrent and photorefractive gain at high applied field. This local field’s effect on an ionic polymer is further confirmed experimentally by comparing the photoconduction of a similar nonionic polymer. © 1998 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
73.50.Pz Photoconduction and photovoltaic effects
78.20.Jq Electro-optical effects
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.66.Qn Polymers; organic compounds
78.20.Fm Birefringence

Beam quality enhancement for a radio-frequency excited annular CO2 laser

A. Lapucci, M. Ciofini, S. Mascalchi, E. Di Fabrizio, and M. Gentili

Appl. Phys. Lett. 73, 2549 (1998); http://dx.doi.org/10.1063/1.122529 (3 pages) | Cited 2 times

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We report the preliminary experimental results obtained from an annular radio-frequency excited CO2 laser with a Talbot cavity and a phase correcting mirror external to the cavity. The Talbot cavity is adopted in order to reduce the number of oscillating azimuthal modes. The use of the external profile-modulated mirror is aimed at reducing the beam phase modulation and thus increasing the amount of fundamental annular mode energy content. The beam quality results to be sensibly increased. © 1998 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.79.Bh Lenses, prisms and mirrors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Stability of above threshold ionization spectrum during intense-field ionization of H2+ near Rc

S. X. Hu, W. X. Qu, and Z. Z. Xu

Appl. Phys. Lett. 73, 2552 (1998); http://dx.doi.org/10.1063/1.122530 (3 pages) | Cited 6 times

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With the collinear model for H2+, we have numerically investigated the photoelectron spectrum of hydrogen molecular ions exposed to an ultrashort intense laser pulse. Above-threshold ionization (ATI) peaks and their temporal evolution are carefully analyzed. We find that once the photon-energy-spaced photoelectron peaks appear, their positions will not shift during the interaction. The stability of ATI spectrum is attributed to the fact that the Stark-shifted ionization potential of H2+ exhibits a minimum plateau during the internuclear distance Rc = 3.6–6 bohr in which the stretching H2+ is significantly ionized. © 1998 American Institute of Physics.
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33.80.Eh Autoionization, photoionization, and photodetachment
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.60.+q Photoelectron spectra
33.57.+c Magneto-optical and electro-optical spectra and effects

Faster grating buildup characteristics in low silanol-containing polysilane-based photorefractive polymer

Fumito Nishida, Nobuo Kushibiki, and Yasuo Tomita

Appl. Phys. Lett. 73, 2555 (1998); http://dx.doi.org/10.1063/1.122531 (3 pages) | Cited 3 times

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The effect of silanol content on the grating buildup dynamics was examined by preparing two different lots of polymethylphenylsilane (PMPS). While the high silanol-containing PMPS showed very sluggish grating formation time, the lower silanol-containing PMPS exhibited very rapid grating formation in a diffraction efficiency measurement. The diffraction efficiency, on the other hand, was found to be unaffected. The results suggest that the silanol is acting as hole trap and a reduction of its content is a key to improving the response characteristics of polysilane-based photoconducting electro-optic polymer composite for photorefractive applications. © 1998 American Institute of Physics.
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42.70.Jk Polymers and organics
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Dj Gratings
72.40.+w Photoconduction and photovoltaic effects
71.55.Ht Other nonmetals
78.20.Jq Electro-optical effects

High-speed maskless laser patterning of indium tin oxide thin films

O. Yavas and M. Takai

Appl. Phys. Lett. 73, 2558 (1998); http://dx.doi.org/10.1063/1.122532 (3 pages) | Cited 22 times

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Patterning characteristics of indium tin oxide thin films using different wavelengths of a diode-pumped Q-switched Nd:YLF and a flashlamp-pumped Nd:YAG laser have been studied. While a ripplelike structure in the etched line was formed due to incomplete material removal when the first harmonic of the Nd:YLF or Nd:YAG laser was used, a residue-free line could be obtained using the fourth harmonic of the Nd:YLF laser even at higher scan speeds. The observed differences in the morphology could be attributed to different absorption characteristics at the infrared and ultraviolet wavelengths. High process speeds in excess of 1 m/s could be achieved. © 1998 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
42.62.Cf Industrial applications
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors

Dual-color polymer light-emitting pixels processed by hybrid inkjet printing

Shun-Chi Chang, Jayesh Bharathan, Yang Yang, Roger Helgeson, Fred Wudl, Michael B. Ramey, and John R. Reynolds

Appl. Phys. Lett. 73, 2561 (1998); http://dx.doi.org/10.1063/1.122533 (3 pages) | Cited 56 times

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A hybrid inkjet printing (HIJP) technology, which combines a pin-hole free polymer buffer layer and an inkjet printed polymer layer, allows the patterning of high quality polymer light-emitting devices. In this letter, we present a successful demonstration of controllable patterning of dual-color polymer light-emitting pixels using this HIJP technique. In this demonstration, the polymer buffer layer is a wide band gap, blue emitting semiconducting polymer prepared by the spin-casting technique. The inkjet printed layer is a red-orange semiconducting polymer which was printed onto the buffer layer. When a proper solvent was selected, the printed polymer diffused into the buffer layer and efficient energy transfer took place generating a red-orange photoluminescence and electroluminescence from the inkjet printed sites. Based on this principle, blue and orange-red dual-color polymer light-emitting pixels were fabricated on the same substrate. The use of this concept represents an entirely new technology for fabricating polymer multicolor displays with high-resolution, lateral patterning capability. © 1998 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
42.70.Jk Polymers and organics
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

1.3 μm room-temperature GaAs-based quantum-dot laser

D. L. Huffaker, G. Park, Z. Zou, O. B. Shchekin, and D. G. Deppe

Appl. Phys. Lett. 73, 2564 (1998); http://dx.doi.org/10.1063/1.122534 (3 pages) | Cited 374 times

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Room-temperature lasing at the wavelength of 1.31 μm is achieved from the ground state of an InGaAs/GaAs quantum-dot ensemble. At 79 K, a very low threshold current density of 11.5 A/cm2 is obtained at a wavelength of 1.23 μm. The room-temperature lasing at 1.31 μm is obtained with a threshold current density of 270 A/cm2 using high-reflectivity facet coatings. The temperature-dependent threshold with and without high-reflectivity end mirrors is studied, and ground-state lasing is obtained up to the highest temperature investigated of 324 K. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Characterization of catastrophic optical damage in Al-free InGaAs/InGaP 0.98 μm high-power lasers

K. H. Park, J. K. Lee, D. H. Jang, H. S. Cho, C. S. Park, K. E. Pyun, J. Y. Jeong, S. Nahm, and J. Jeong

Appl. Phys. Lett. 73, 2567 (1998); http://dx.doi.org/10.1063/1.122557 (3 pages) | Cited 16 times

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Catastrophic optical damage (COD) in Al-free InGaAs/InGaP 0.98 μm lasers has been investigated using real-time electroluminescence (EL) and transmission electron microscopy (TEM). From EL images, we observed that multiple bright spots initiated from one of the facets and then propagated to the center of the cavity during the COD process. It is clarified by the TEM analysis that the propagation of bright spots resulted in 60-nm-wide Moiré fringe along the cavity and the crystalline phase of the active area became polycrystalline. Highly nonradiative polycrystalline phase of the active area is the major cause of COD failure in the Al-free 0.98 μm lasers. © 1998 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Fd III-V semiconductors
42.55.Px Semiconductor lasers; laser diodes

Change in luminescence properties of porous Si by F2 and D2O exposure: In situ photoluminescence, Raman, and Fourier-transform infrared spectral study

T. Wadayama, T. Arigane, and A. Hatta

Appl. Phys. Lett. 73, 2570 (1998); http://dx.doi.org/10.1063/1.122508 (3 pages) | Cited 9 times

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In situ photoluminescence (PL), Raman, and infrared (IR) spectra of porous Si (PS) during F2/D2O exposures were investigated. F2 exposure at 298 K resulted in a peak shift of PL band from 750 to 670 nm with an intensity reduction. IR spectra revealed that the surface hydrogenated Si of the PS was displaced by fluorinated one. By subsequent D2O exposure, the PL band further shifted to a shorter wavelength with a significant intensity increase: IR bands due to surface oxides as well as SiD and SiOD bonds were observed after the exposure. On the contrary, the average size of the Si crystallites in the PS evaluated from Raman spectra remained almost unchanged throughout the exposures. These results suggest that surface chemistry plays a crucial role in the PL of the PS. © 1998 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
81.05.Cy Elemental semiconductors
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
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A displacement amplifier using mechanical demodulation

Riccardo Carotenuto, Antonio Iula, Massimo Pappalardo, and Nicola Lamberti

Appl. Phys. Lett. 73, 2573 (1998); http://dx.doi.org/10.1063/1.122509 (3 pages)

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Piezoelectric ceramics can provide electromechanical transduction with high stresses but low displacements. To obtain larger displacements, several mechanical amplifying structures have been used. High alternating displacements can be obtained using resonant structures. We propose a displacement amplifier based on a mechanical rectifier, able to take advantage of the high displacements of resonant structures, and capable of obtaining a continuous displacement. A prototype composed of a Langevin resonator coupled to a mass–spring–damper system, acting as the rectifier, was constructed. Interferometric measurements on the proposed mechanical demodulator were carried out, validating the principle of operation. The possible applications are in the field of fast valves and micrometric positioning. © 1998 American Institute of Physics.
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06.60.Sx Positioning and alignment; manipulating, remote handling
07.10.-h Mechanical instruments and equipment
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.65.Fs Electromechanical resonance; quartz resonators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
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Dynamics of electron beam ablation of silicon dioxide measured by dye laser resonance absorption photography

S. D. Kovaleski, R. M. Gilgenbach, L. K. Ang, and Y. Y. Lau

Appl. Phys. Lett. 73, 2576 (1998); http://dx.doi.org/10.1063/1.122510 (3 pages) | Cited 5 times

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The dynamics of electron beam ablation plumes have been characterized through the application of dye laser resonance absorption photography. The ablation of fused silica by a channelspark electron beam was studied by probing the near-ground state, 3p2 1D−4s 1P0 neutral Si transition at 288.158 nm. Necessary background gases (Ar or N2) were tested at pressures of 15 or 30 mTorr. A two-lobed, Si atom plume shape was discovered that is hydrodynamically more complex than laser ablation plumes. These plumes merge into a single-lobed plume at about 400 ns after the e-beam current pulse rise. Plume front expansion velocities of Si atoms were measured at nearly 1 cm/μs, and are comparable to the expansion of laser ablated metal atom plumes with laser fluences of a few J/cm2. © 1998 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
79.20.Kz Other electron-impact emission phenomena
07.68.+m Photography, photographic instruments; xerography
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Stress and relief of misfit strain of Ge/Si(111)

J. Walz, A. Greuer, G. Wedler, T. Hesjedal, E. Chilla, and R. Koch

Appl. Phys. Lett. 73, 2579 (1998); http://dx.doi.org/10.1063/1.122511 (3 pages) | Cited 15 times

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The intrinsic stress and morphology of the Stranski–Krastanow system Ge/Si(111) have been investigated at deposition temperatures of 700–950 K. In a broad range of intermediate temperatures, only one distinct decline of stress is observed at the onset of three-dimensional islanding. Supported by a recent transmission electron microscopy study, the results demonstrate that the strain of Ge/Si(111), where the substrate surface in contrast to Ge/Si(001) is the glide plane for dislocations, is relieved by incorporation and continuous rearrangement of dislocations during the island stage. © 1998 American Institute of Physics.
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68.35.Ct Interface structure and roughness
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Microstructure of Ti/Al ohmic contacts for n-AlGaN

S. Ruvimov, Z. Liliental-Weber, J. Washburn, D. Qiao, S. S. Lau, and Paul K. Chu

Appl. Phys. Lett. 73, 2582 (1998); http://dx.doi.org/10.1063/1.122512 (3 pages) | Cited 61 times

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Transmission electron microscopy was employed to evaluate the microstructure of Al/Ti ohmic contacts to AlGaN/GaN heterostructure field-effect transistor structures. Contact resistance was found to depend on the structure and composition of the metal and AlGaN layers, and on atomic structure of the interface. A 15–25-nm-thick interfacial AlTi2N layer was observed at the contact-AlGaN interface. Formation of such nitrogen-containing layers appears to be essential for ohmic behavior on n-type III-nitride materials suggesting a tunneling contact mechanism. Contact resistivity was found to increase with Al fraction in the AlGaN layer. © 1998 American Institute of Physics.
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85.30.Tv Field effect devices
73.40.Ns Metal-nonmetal contacts
68.35.Ct Interface structure and roughness
73.40.Cg Contact resistance, contact potential

Polytypoid structures in annealed In2O3–ZnO films

Y. Yan, S. J. Pennycook, J. Dai, R. P. H. Chang, A. Wang, and T. J. Marks

Appl. Phys. Lett. 73, 2585 (1998); http://dx.doi.org/10.1063/1.122513 (3 pages) | Cited 27 times

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Atomic-resolution Z-contrast images demonstrate unambiguously that the annealed, metalorganic chemical vapor deposition derived transparent In2O3–ZnO films have a polytypoid microstructure, consisting of ZnO slabs of variable width separated by single In–O octahedral layers. These In–O layers induce a polarity inversion in the two adjacent ZnO layers, which is reversed again by a mirror domain boundary inside each ZnO slab. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Observation of CuPt-A type atomic ordering in AlxIn1−xAs alloys

Tohru Suzuki, Toshinari Ichihashi, and Tatsuo Nakayama

Appl. Phys. Lett. 73, 2588 (1998); http://dx.doi.org/10.1063/1.122514 (3 pages) | Cited 7 times

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CuPt-A type atomic ordering, which has been reported for only Al0.5In0.5P and Ga0.5In0.5P, was observed in Al-rich AlxIn1−xAs grown on (001) InP substrates by solid-source molecular-beam epitaxy; only the triple-period-A type ordering in the [111]A directions has been previously reported for this alloy system grown under a similar growth condition. While the triple-period-A type ordering was observed in Al0.5In0.5As grown with a (2×3) surface reconstruction, the CuPt-A type ordering was observed in Al-rich AlxIn1−xAs when the surface showed a (1×2) surface reconstruction during growth. This observation provides strong support for the previous inference that the (1×2) surface reconstruction gives rise to CuPt-A type ordering. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.66.Fn Inorganic compounds

Structure and optical properties of amorphous diamond films prepared by ArF laser ablation as a function of carbon ion kinetic energy

Vladimir I. Merkulov, Douglas H. Lowndes, G. E. Jellison, A. A. Puretzky, and D. B. Geohegan

Appl. Phys. Lett. 73, 2591 (1998); http://dx.doi.org/10.1063/1.122515 (3 pages) | Cited 40 times

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Amorphous carbon films with variable sp3 content were produced by ArF (193 nm) pulsed laser deposition. Electron energy loss spectroscopy and spectroscopic ellipsometry were employed to systematically study changes in the bonding and optical properties of the carbon films as a function of the kinetic energy of ablated C ions, which was measured using an ion probe. The measurements reveal that the films with the most diamond-like properties are obtained at the C ion kinetic energy of ∼90 eV. In contrast to measurements made as a function of laser fluence, ion probe measurements of kinetic energy are a convenient as well as more accurate and fundamental method for monitoring deposition conditions, with the advantage of being readily transferable for interlaboratory comparisons. © 1998 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
61.43.Dq Amorphous semiconductors, metals, and alloys
78.66.Db Elemental semiconductors and insulators
81.05.ub Fullerenes and related materials
81.15.Fg Pulsed laser ablation deposition
79.20.Kz Other electron-impact emission phenomena
68.55.-a Thin film structure and morphology
81.05.Gc Amorphous semiconductors

Influence of the water layer on the shear force damping in near-field microscopy

S. Davy, M. Spajer, and D. Courjon

Appl. Phys. Lett. 73, 2594 (1998); http://dx.doi.org/10.1063/1.122516 (3 pages) | Cited 28 times

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The influence of the water layer on the shear force damping is investigated in the case of a perfectly flat mica surface. In ambient conditions it is shown that the damping curve exhibits three particular regimes depending on the tip-sample distance. Moreover, the damping varies significantly over the first hour, pointing out the complexity of the distance control by shear force detection. © 1998 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
68.35.Gy Mechanical properties; surface strains

Contrast reversal in scanning capacitance microscopy imaging

Robert Stephenson, Anne Verhulst, Peter De Wolf, Matty Caymax, and Wilfried Vandervorst

Appl. Phys. Lett. 73, 2597 (1998); http://dx.doi.org/10.1063/1.122517 (3 pages) | Cited 21 times

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We have investigated the quantification properties of scanning capacitance microscopy (SCM) by using two dedicated test structures and highlight the response of SCM to changes in dopant density. Our results indicate that contrast reversal occurs and that the SCM output is not always a monotonically increasing signal with decreasing dopant density. Two epitaxially grown staircase structures covering the doping ranges 1014–1020 cm−3 p type and 5×1014–5×1019 cm−3 n type were produced for this study as the turning point in the response function typically occurs at a doping level of around 1017 cm−3. Through the use of a simple simulation model we see that contrast reversal is expected due to a relative shift between the dC/dV curves for different doping levels. The onset of contrast reversal can be adjusted by changing the dc sample bias leading to a shift in the operating position of the SCM, and the significance of this point will be discussed here. © 1998 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components
07.50.-e Electrical and electronic instruments and components
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
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Direct micropatterning of Si and GaAs using electrochemical development of focused ion beam implants

P. Schmuki and L. E. Erickson

Appl. Phys. Lett. 73, 2600 (1998); http://dx.doi.org/10.1063/1.122518 (3 pages) | Cited 4 times

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Focused ion beam implantation of Si++ was used to write defined surface damage/implant patterns into n-type GaAs (100) and Si (100) substrates. These implant sites represent initiation sites for dissolution processes when electrochemically polarized in HCl or HF electrolytes, respectively. Selective dissolution within the patterns is achieved if anodic polarization of the n-type material is carried out in the dark at potentials below (cathodic to) the onset of dissolution potential of the unimplanted surface. Uniform etching within the implanted region takes place, when local electropolishing conditions are established. Thus, highly defined etch patterns, e.g., lines, gratings, or pits, can be produced in the submicron range. The depth of the etched patterns corresponds to the implant/damage profile created in the implantation process and etch stop occurs at less reactive crystal planes. © 1998 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.65.Ps Polishing, grinding, surface finishing
61.72.uf Ge and Si
61.72.uj III-V and II-VI semiconductors

Initial carrier relaxation dynamics in ion-implanted Si nanocrystals: Femtosecond transient absorption study

V. I. Klimov, Ch. J. Schwarz, D. W. McBranch, and C. W. White

Appl. Phys. Lett. 73, 2603 (1998); http://dx.doi.org/10.1063/1.122519 (3 pages) | Cited 31 times

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Transient absorption spectra of ion-implanted Si nanocrystals (NCs) exhibit two picosecond photoinduced absorption features, attributed to carriers in NC quantized states (high-energy band) and Si/SiO2 interface states (low-energy band). Fast relaxation of the high-energy band indicates that populations of quantized states are short lived and decay on the sub-10-ps time scale due to efficient surface trapping. This shows that the red emission in our samples is not due to carriers in quantized states but rather is a result of deactivation of surface traps. © 1998 American Institute of Physics.
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61.72.uf Ge and Si
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.40.Fy Semiconductors
72.80.Cw Elemental semiconductors
61.46.-w Structure of nanoscale materials

Raman and x-ray studies of InN films grown by metalorganic vapor phase epitaxy

Ming-Chih Lee, Heng-Ching Lin, Yung-Chung Pan, Chen-Ke Shu, Jehn Ou, Wen-Hsiung Chen, and Wei-Kuo Chen

Appl. Phys. Lett. 73, 2606 (1998); http://dx.doi.org/10.1063/1.122520 (3 pages) | Cited 32 times

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Thin InN films were deposited on the (0001) sapphire substrate at various temperatures from 325 to 600 °C by metalorganic vapor phase epitaxy. We used Raman scattering and x-ray diffraction to investigate the film properties and crystalline structures. Significant line broadening, softening and intensity evolution were observed at the growth temperatures between 375 and 450 °C. This can be attributed to the formation of the mixed hexagonal and cubic structures and the related dislocation defects. As the growth temperature is further increased, the hexagonal phase is found to be dominant in the deposited InN film. © 1998 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology

Significance of tunneling in p+ amorphous silicon carbide n crystalline silicon heterojunction solar cells

M. W. M. van Cleef, R. E. I. Schropp, and F. A. Rubinelli

Appl. Phys. Lett. 73, 2609 (1998); http://dx.doi.org/10.1063/1.122521 (3 pages) | Cited 13 times

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We used the internal photoemission (IPE) technique to accurately determine the valence and conduction band offsets at the a-SiC:H/c-Si interface and investigated with numerical simulations their effects on the photocarrier collection in p+ a-SiC:H/n c-Si heterojunction solar cells. The valence and conduction band discontinuities were found to be 0.60 and 0.55 eV, respectively. However, despite the large barrier at the valence band edge, 30 nm p+ a-SiC:H/n c-Si heterojunction solar cells show no collection problems due to blocking of holes (FF = 0.73). Combined IPE measurements and simulation results indicate that tunneling of holes through this barrier at the valence band edge can explain the unhindered collection. © 1998 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Jc Amorphous semiconductors; glasses
73.61.Cw Elemental semiconductors

Field-dependent absorption in superlattices: Comparison of theory and experiment

A. Thränhardt, H. J. Kolbe, J. Hader, T. Meier, G. Weiser, and S. W. Koch

Appl. Phys. Lett. 73, 2612 (1998); http://dx.doi.org/10.1063/1.122522 (3 pages) | Cited 6 times

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Absorption and differential electroabsorption spectra of a GaInAs/InP superlattice in the regime of Wannier–Stark localization are compared with spectra derived from the Semiconductors Bloch Equations. The absorption is strongly underestimated for higher energies by the effective mass approximation but good agreement is achieved by using an energy dependent in-plane effective mass. No fitting parameters are used except for a phenomenological broadening. The lineshape of the field-modulated spectra is dominated by the strong field dependence of Wannier–Stark transitions and depends on the amplitude of the modulating field which should be kept small for best results. © 1998 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Formation of self-assembled GaAs/AlGaAs quantum dots by low-temperature epitaxy

Chae-Deok Lee, Chanro Park, Hwack Joo Lee, S. K. Noh, Kyu-Seok Lee, and Seong-Ju Park

Appl. Phys. Lett. 73, 2615 (1998); http://dx.doi.org/10.1063/1.122523 (3 pages) | Cited 8 times

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We report the direct formation of self-assembled GaAs/AlGaAs quantum dots by low-temperature molecular beam epitaxy. To drive a three dimensional growth mode, the (1×1) AlGaAs surface was exposed alternately to the Ga and As sources. The resulting GaAs nanocrystals having {111} facets were clearly identified by high-resolution transmission electron microscopy. The emission spectra also confirmed the formation of dots. The transition to a three-dimensional growth mode is attributed to the limited surface migration of Ga adatoms on the AlGaAs surface, which has excess As at low substrate temperature. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.61.Ey III-V semiconductors
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