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29 Jan 1996

Volume 68, Issue 5, pp. 579-723

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Scanning near‐field optical microscope using an atomic force microscope cantilever with integrated photodiode

S. Akamine, H. Kuwano, and H. Yamada

Appl. Phys. Lett. 68, 579 (1996); http://dx.doi.org/10.1063/1.116504 (3 pages) | Cited 21 times

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A combined atomic force and scanning near‐field optical microscope is presented. The critical component of the instrument is a single crystal silicon, microfabricated force‐sensing cantilever with an integrated photodiode. Near‐field optical images are obtained by monitoring variations in the optical power detected by the photodiode while the cantilever tip is scanned in an evanescent optical field created by illuminating the sample by total internal reflection. Near‐field optical power was detected at tip‐sample spacings of one‐quarter wavelength. Atomic force and scanning near‐field optical microscope images of the same samples show corresponding features as small as 25 nm. © 1996 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
07.79.Lh Atomic force 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

Determination of losses, gain, and pumping‐beam mode overlap for Q‐switched end‐pumped lasers

B. Ozygus and K. Ziegler

Appl. Phys. Lett. 68, 582 (1996); http://dx.doi.org/10.1063/1.116505 (2 pages)

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A method to determine the losses and the gain of a Q‐switched four‐level laser is presented. For an end‐pumped system with an additional measurement of relaxation oscillation frequencies the pumping‐beam and laser mode overlap can be determined. Since no resonator changes are necessary, the measurement is very easy to perform. With losses, gain, and overlap determined, everything is known to optimize the system. © 1996 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optical properties of glasses containing copper oxide particles

R. J. Araujo, J. Butty, and N. Peyghambarian

Appl. Phys. Lett. 68, 584 (1996); http://dx.doi.org/10.1063/1.116506 (3 pages) | Cited 6 times

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Particles of cuprous oxide with 20 nm sizes have been precipitated from borosilicate glasses. The absorption spectra show distinct changes in glasses given different heat treatments. Only very weak nonlinear effects are observed. © 1996 American Institute of Physics.
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78.40.-q Absorption and reflection spectra: visible and ultraviolet
78.66.Vs Fine-particle systems

Picosecond four‐wave‐mixing in GaN epilayers at 532 nm

Bahman Taheri, J. Hays, J. J. Song, and B. Goldenberg

Appl. Phys. Lett. 68, 587 (1996); http://dx.doi.org/10.1063/1.116476 (3 pages) | Cited 11 times

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Pulsed probe degenerate four wave mixing experiments were performed on GaN epilayers using 13 ps pulses at 532 nm. Intensity and time response of the scattering efficiency was studied. Intensity dependence of the observed signal suggests carrier generation by both single and two photon effects. The absolute scattering efficiency was measured and related to pump‐induced nonlinear index change. The nonlinear refractive coefficient found was 1×10−3 cm2/GW which is greater than an order of magnitude larger than the expected value. Time response of the signal was found to be dictated by carrier lifetimes. Double‐exponential decays to trap levels with lifetimes of 100 ps and 1.1 ns are suggested as the dominant recombination processes. © 1996 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors

Transverse mode dynamics in vertical cavity surface emitting lasers excited by fast electrical pulses

O. Buccafusca, J. L. A. Chilla, J. J. Rocca, S. Feld, C. Wilmsen, V. Morozov, and R. Leibenguth

Appl. Phys. Lett. 68, 590 (1996); http://dx.doi.org/10.1063/1.116477 (3 pages) | Cited 29 times

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We report measurements of the transient multimode dynamics of vertical cavity surface emitting lasers excited by short (100–200 ps rise times, 1 ns duration) electrical pulses. Fast changes on the spatial distribution of the output power and strong mode competition are observed. Numerical simulations show that the observed dynamics are due to the partial overlap of the different transverse modes through spatial hole burning. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Solid‐state dye lasers based on polymers incorporating covalently bonded modified rhodamine 6G

A. Costela, I. Garcia‐Moreno, J. M. Figuera, F. Amat‐Guerri, and R. Sastre

Appl. Phys. Lett. 68, 593 (1996); http://dx.doi.org/10.1063/1.116478 (3 pages) | Cited 21 times

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We report on the lasing action of modified rhodamine 6G dyes copolymerized with methacrylic monomers. The laser samples were transversely pumped with a N2 laser at 337 nm. Lasing efficiencies similar to those found for rhodamine 6G in ethanol solution have been achieved. Important increases in photostability, with lifetimes in excess of 20 000 shots at 2 Hz, have been obtained. By using a rotating mechanism, a stable output with no sign of degradation after half a million shots has been demonstrated. © 1996 American Institute of Physics.
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42.55.Mv Dye lasers
42.60.-v Laser optical systems: design and operation

Optical probing of the temperature transients during pulsed‐laser induced boiling of liquids

Hee K. Park, Costas P. Grigoropoulos, Chie C. Poon, and Andrew C. Tam

Appl. Phys. Lett. 68, 596 (1996); http://dx.doi.org/10.1063/1.116479 (3 pages) | Cited 26 times

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The thermodynamics of the rapid boiling of a liquid on a solid surface heated by an excimer laser pulse is studied experimentally. The dynamics of bubble nucleation, growth, and collapse is detected by probing the optical specular reflectance. The transient temperature field is measured by monitoring the reflectance of a thin film with calibrated optical properties. The metastability behavior of the liquid and the criterion for the liquid‐vapor phase transition in nanosecond time scale are obtained for the pressure from 1 atmosphere to 3.3 MPa. © 1996 American Institute of Physics.
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64.60.My Metastable phases
64.70.F- Liquid-vapor transitions
79.20.Ds Laser-beam impact phenomena

First order gain and index coupled distributed feedback lasers in ZnSe‐based structures with finely tunable emission wavelengths

D. Eisert, G. Bacher, N. Mais, J. P. Reithmaier, A. Forchel, B. Jobst, D. Hommel, and G. Landwehr

Appl. Phys. Lett. 68, 599 (1996); http://dx.doi.org/10.1063/1.116480 (3 pages) | Cited 7 times

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First order gain and index coupled distributed feedback (DFB) gratings were realized in ZnSe‐based laser structures using direct implantation with a focused ion beam for gain‐modulated structures and conventional electron beam lithography for index modulation. With both technologies, gratings with periods below 90 nm could be achieved, permitting DFB emission in the blue spectral range. Fine tuning of the emission wavelength in steps of 0.14 nm is demonstrated by sampled DFB gratings based on a periodic modulation of the resonator period. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Infrared‐to‐visible CW frequency upconversion in Er3+‐doped fluoroindate glasses

Cid B. de Araújo, L. S. Menezes, G. S. Maciel, L. H. Acioli, A. S. L. Gomes, Y. Messaddeq, A. Florez, and M. A. Aegerter

Appl. Phys. Lett. 68, 602 (1996); http://dx.doi.org/10.1063/1.116481 (3 pages) | Cited 40 times

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We report on efficient frequency upconversion in Er3+‐doped fluoroindate glasses. The process is observed under 1.48 μm laser diode excitation and results in the generation of strong blue (∼407 nm), green (∼550 nm), and red (∼670 nm) radiation. The main mechanism that allows for upconversion appears to be the energy transfer among Er3+ ions in excited states. The results illustrate the large potential of this new class of glasses for photonic applications. © 1996 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz

Uniparabolic mirror grading for vertical cavity surface emitting lasers

K. L. Lear and R. P. Schneider

Appl. Phys. Lett. 68, 605 (1996); http://dx.doi.org/10.1063/1.116482 (3 pages) | Cited 30 times

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We report details of mirror grading profiles for high efficiency vertical cavity surface emitting lasers. The mirrors provide low vertical resistance in conjunction with improvements in optical reflectivity, thermal conductivity, and lateral electrical conductivity in comparison to earlier grading profiles. The enhancement of these properties is verified by a comparison of thermal resistance and total electrical resistance for lasers of varying size. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

The second harmonic component in the Bessel beam

Desheng Ding and Zuhong Lu

Appl. Phys. Lett. 68, 608 (1996); http://dx.doi.org/10.1063/1.116483 (3 pages) | Cited 10 times

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The analysis is based on the Khokhlov–Zabolotskaya–Kuznetsov wave equation. Analytical and approximate solutions are derived for the second harmonic component in the Bessel nondiffracting beam. The theoretical results indicate that the second harmonic beam is nearly nondiffracting in the radial direction and the pressure amplitude is proportional to the square root of propagation distance in the quasilinear approximation, and that the beamwidth of the second harmonic is just 1/2 times that of the fundamental component in the Bessel field, not as 1/√2 times in the fields radiated by other sources. © 1996 American Institute of Physics.
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42.25.-p Wave optics

Observation of folded acoustic phonons in a porous silicon superlattice

Xing‐Long Wu, Feng Yan, Feng‐Ming Pan, Xi‐mao Bao, Shu‐Sheng Jiang, Ming‐Sheng Zhang, and Duan Feng

Appl. Phys. Lett. 68, 611 (1996); http://dx.doi.org/10.1063/1.116484 (2 pages) | Cited 4 times

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Porous silicon superlattice was fabricated and its Raman spectra were examined. The clear zone‐folded doublets from longitudinal acoustic phonons were obtained up to fourth order. A similar phenomenon was not observed in ordinary porous silicon. Using the elastic continuum model, we calculated the frequencies of these folded doublets and the obtained results were in excellent agreement with the experimental ones. © 1996 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.30.Hv Other nonmetallic inorganics

Scaling laws for particle growth in plasma reactors

D. S. Lemons, R. K. Keinigs, D. Winske, and Michael E. Jones

Appl. Phys. Lett. 68, 613 (1996); http://dx.doi.org/10.1063/1.116485 (3 pages) | Cited 14 times

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We quantify a model which incorporates observed features of contaminant particle growth in plasma processing reactors. According to the model, large ‘‘predator’’ particles grow by adsorbing smaller, typically neutral, ‘‘prey’’ protoparticles. The latter are supplied by an assumed constant mass injection of contaminant material. Scaling laws and quantitative predictions compare favorably with published experimental results. © 1996 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Metalorganic chemical vapor deposition of ferroelectric SrBi2Ta2O9 thin films

Tingkai Li, Yongfei Zhu, Seshu B. Desu, Chien‐Hsiung Peng, and Masaya Nagata

Appl. Phys. Lett. 68, 616 (1996); http://dx.doi.org/10.1063/1.116486 (3 pages) | Cited 133 times

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Ferroelectric layered‐oxides SrBi2Ta2O9 thin films were prepared on Pt coated Si wafers and single‐crystal sapphire by metalorganic chemical vapor deposition (MOCVD). The films were specular and crack‐free and showed complete crystallization at temperatures between 650 and 700 °C. Good ferroelectric properties were obtained for a 200 nm thick film with Pt electrodes: 2Pr and Ec were about 8.3 μC/cm2 and 60 kV/cm, respectively. The leakage currents were as low as 8×10−9 A/cm2 at 150 kV/cm. The films also showed fatigue‐free characteristics: no fatigue was observed up to 1.4×1010 switching cycles. These high quality MOCVD films make high‐intensity (≳1 Mbit) nonvolatile memory devices possible. © 1996 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

All optical switching based on intensity induced absorption in C60

Fryad Z. Henari, Karl H. Cazzini, Declan N. Weldon, and Werner J. Blau

Appl. Phys. Lett. 68, 619 (1996); http://dx.doi.org/10.1063/1.116487 (3 pages) | Cited 9 times

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In this letter, we demonstrate that the strong reverse saturation which has been observed at high intensity in a C60 solution, is also manifest at a low intensity. The behavior fits well to a rate equation model based on a six level system with known photophysical parameters. Furthermore, we demonstrate that it can be utilized to generate optical switching and bistability. © 1996 American Institute of Physics.
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42.65.-k Nonlinear optics
78.40.Ri Fullerenes and related materials

Electrical properties of boron nitride thin films grown by neutralized nitrogen ion assisted vapor deposition

Ming Lu, A. Bousetta, A. Bensaoula, K. Waters, and J. A. Schultz

Appl. Phys. Lett. 68, 622 (1996); http://dx.doi.org/10.1063/1.116488 (3 pages) | Cited 26 times

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Boron nitride (BN) thin films (containing mixed cBN/hBN phase) have been deposited on Si(100) substrates using neutralized nitrogen beam and electron beam evaporation of boron. All as‐deposited BN films were p type with a room‐temperature carrier concentration in the range of 5×1016 to 1×1017 cm−3. The Mg‐doped BN films showed carrier concentrations in the range of 1.2×1018 cm−3 to 5.2×1018 cm−3 when the Mg cell temperature was varied from 250 to 500 °C. The films were analyzed for both majority elements (B and N) and dopant/impurity (Si, Mg, Fe, etc.) incorporation using secondary ion mass spectroscopy and mass spectroscopy of recoiled ions (MRSI). MRSI is shown to be superior for dopant characterization of boron nitride thin films. © 1996 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating

Structurally relaxed models of the Si(001)–SiO2 interface

Alfredo Pasquarello, Mark S. Hybertsen, and Roberto Car

Appl. Phys. Lett. 68, 625 (1996); http://dx.doi.org/10.1063/1.116489 (3 pages) | Cited 70 times

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We present a first‐principles investigation of the structural properties of two models for the Si(001)–SiO2 interface. The models derive from attaching tridymite, a crystalline form of SiO2, to Si(001), and then allowing for full relaxation. These models do not show electronic states in the silicon gap, as required by electrical experiments. They contain the three intermediate oxidation states of silicon, consistent with photoemission experiments. We study bond length and bond angle distributions and measures of local strain. The strain is localized to a transition region at the interface. Strain does not persist in the full oxide. © 1996 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Conversion of step configuration induced by strain in Si1−xGex layers deposited on vicinal Si(001) surface

J. M. Zhou, L. W. Guo, Q. Cui, C. S. Peng, and Q. Huang

Appl. Phys. Lett. 68, 628 (1996); http://dx.doi.org/10.1063/1.116490 (3 pages) | Cited 8 times

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Reflection high energy electron diffraction (RHEED) intensity measurements reveal that the strain in a Si1−xGex layer on a vicinal Si(001) surface converts a (1×2) domain dominated step configuration to a (2×1) domain dominated one. The dependence of the effect on the Ge content is similar to the dependence of the critical thickness of the pseudomorphic growth of Si1−xGex layers on Ge content. No conversion effect has been observed on exact Si(001) substrates. © 1996 American Institute of Physics.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
68.55.-a Thin film structure and morphology

Stripe patterns formed by the thermal desorption of Ga atoms on Ga‐terminated Si(111) surfaces

K. Fujita, Y. Kusumi, and M. Ichikawa

Appl. Phys. Lett. 68, 631 (1996); http://dx.doi.org/10.1063/1.116491 (3 pages) | Cited 17 times

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The Si(111)‐7×7 area surrounded by the Si(111)‐√3×√3R30°‐Ga region has been observed by scanning tunneling microscopy during the thermal desorption of Ga atoms at ∼600 °C and after the desorption. The 7×7 area exhibits triangular and strip patterns on the nanometer scale for the Si(111) substrates tilting toward the [112] and [112] directions, respectively. This is because faulted halves of the 7×7 reconstruction are adjacent to the √3×√3‐Ga area on the boundary between the 7×7 and √3×√3‐Ga areas during Ga desorption. It has been found that strip patterns with nanometer‐scale precision are formed on the Si(111) substrates tilting toward the [112] direction. © 1996 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.-b Surface treatments

Crystalline carbon nitride films formation by chemical vapor deposition

Yafei Zhang, Zhonghua Zhou, and Hulin Li

Appl. Phys. Lett. 68, 634 (1996); http://dx.doi.org/10.1063/1.116492 (3 pages) | Cited 77 times

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Crystalline carbon nitride films have been synthesized in a rf plasma assisted hot filament chemical vapor deposition system. Large crystalline grains up to ∼10 μm in size as well as film‐like regions are observed in the morphology of the films. β‐C3N4 with two groups of lattice parameters (one is consistent with the theoretical value and the other is ∼3% smaller) in the deposited films on polycrystalline Ni substrate has been revealed by x‐ray diffraction spectrum (XRD). No Raman shift peaks have been found by Raman scattering measurement, but some presently unknown diffraction peaks appeared in the XRD spectrum. It is proposed that there are possible unknown structures of crystalline C‐N in the films. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Study of yielding mechanics in nanometer‐sized Au contacts

A. Stalder and U. Dürig

Appl. Phys. Lett. 68, 637 (1996); http://dx.doi.org/10.1063/1.116493 (3 pages) | Cited 77 times

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Yielding properties of Au point contacts of nanometer‐scale dimensions have been studied using a scanning tunneling microscope supplemented by a force sensor for measuring tip–sample forces. The contacts are made by indenting the tip typically 10 nm into the substrate, whereby an adhesion neck is formed. Three consecutive deformation phases of the neck can be identified during retraction of the tip: (1) buildup of tensile stress, (2) incomplete fracture, and (3) quasicontinuous plastic flow. Finally the neck breaks when a maximum of three to four atoms are left in the contact. In the plastic flow regime, the conductance and thus the contact area shrink exponentially with elongation of the neck, suggesting that plastic deformation occurs locally within 5 to 6 atomic layers. The stress applied during plastic flow is initially of the order of 10 GPa and gradually increases to ≂ 20 GPa shortly before the neck breaks. Accounting for a surface force contribution, an intrinsic yield strength of the order of 5 to 8 GPa is obtained, which is more than one order of magnitude larger than the macroscopic yield strength of Au. © 1996 American Institute of Physics.
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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
62.20.F- Deformation and plasticity

Study of light induced instability in intrinsic hydrogenated amorphous silicon films by the photomixing technique

Yi Tang, S. Dong, R. Braunstein, and B. von Roedern

Appl. Phys. Lett. 68, 640 (1996); http://dx.doi.org/10.1063/1.116494 (3 pages) | Cited 9 times

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By using the photomixing technique we have found that the drift mobility (μd) of intrinsic hydrogenated amorphous silicon (a‐Si:H) films produced by both glow discharge and hot wire techniques increases with increasing electric field, while the lifetime (τ) decreases with increasing electric field, and the μdτ product is essentially independent of the electric field. We have also found an empirical relationship that a greater field dependence of the drift mobility of an a‐Si:H film in the annealed state indicates a poorer stability of the photoconductivity upon light soaking. © 1996 American Institute of Physics.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Jc Amorphous semiconductors; glasses
84.60.Jt Photoelectric conversion

Role of threading dislocation structure on the x‐ray diffraction peak widths in epitaxial GaN films

B. Heying, X. H. Wu, S. Keller, Y. Li, D. Kapolnek, B. P. Keller, S. P. DenBaars, and J. S. Speck

Appl. Phys. Lett. 68, 643 (1996); http://dx.doi.org/10.1063/1.116495 (3 pages) | Cited 320 times

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In this letter we demonstrate that the anomalously low (002) x‐ray rocking curve widths for epitaxial hexagonal GaN films on (001) sapphire are a result of a specific threading dislocation (TD) geometry. Epitaxial GaN films were grown on c‐plane sapphire by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) in a horizontal flow reactor. Films were grown with (002) rocking curves (ω‐scans) widths as low as 40 arcsec and threading dislocation densities of ∼2×1010 cm−2. The threading dislocations in this film lie parallel to the [001] direction and within the limit of imaging statistics, all are pure edge with Burgers vectors parallel to the film/substrate interface. These TDs will not distort the (002) planes. However, distortion of asymmetric planes, such as (102), is predicted and confirmed in (102) rocking curve widths of 740 arcsec. These results are compared with films with (002) rocking curves of ∼270 arcsec and threading dislocation densities of ∼7×108 cm−2. © 1996 American Institute of Physics.
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61.05.C- X-ray diffraction and scattering
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Effect of thermal annealing on electrical conductivities in arsenic‐ion‐implanted GaAs

Wen‐Chung Chen and C.‐S. Chang

Appl. Phys. Lett. 68, 646 (1996); http://dx.doi.org/10.1063/1.116496 (3 pages) | Cited 4 times

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The effect of thermal annealing on the electrical conductivities of arsenic‐ion‐implanted GaAs has been investigated by deep level transient spectroscopy and temperature‐dependent conductance measurements. For the annealed films of arsenic‐ion‐implanted GaAs a band of deep‐level defects with the activation energy of around 0.55 eV below the conduction band is found. The dense concentration of traps is able to reduce the carrier concentration from 3×1018 to 2×1017 cm−3. The cross section of the deep level is calculated to be 1.5×10−14 cm2. The carrier‐transport mechanisms of both as‐implanted GaAs and postannealed GaAs are dominantly shown to be a separate hopping and active‐type conduction. © 1996 American Institute of Physics.
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71.55.Eq III-V semiconductors

Use of photocurrent difference spectroscopy to determine higher confined states in wide multiquantum well structures

K. Tanaka, N. Kotera, and H. Nakamura

Appl. Phys. Lett. 68, 649 (1996); http://dx.doi.org/10.1063/1.116497 (3 pages) | Cited 4 times

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Using a novel photocurrent difference spectroscopy, six conduction subbands have become observable in 20‐nm‐wide In0.53Ga0.47As/In0.52Al0.48As multiquantum wells. The observed wavelength range was 0.8–1.8 μm. A proper choice of electric fields in the well on the order of 90‐170 kV/cm made it possible to magnify the photocurrent difference spectrum by 1×104, owing to the Stark shift of about 20–100 meV. The interband optical transitions were limited to the field‐sensitive ones of mostly forbidden type. As a result, conduction‐subband eigen energies in the wells were determined at room temperature. © 1996 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
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