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7 Sep 1998

Volume 73, Issue 10, pp. 1311-1448

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Repetition-rate multiplication in actively mode-locked fiber lasers by higher-order FM mode locking using a high-finesse Fabry–Perot filter

Kazi Sarwar Abedin, Noriaki Onodera, and Masaharu Hyodo

Appl. Phys. Lett. 73, 1311 (1998); http://dx.doi.org/10.1063/1.121879 (3 pages) | Cited 17 times

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We demonstrate an FM mode-locking technique for multiplying the pulse repetition rate of lasers by several times above the modulation frequency. The mode locking of the laser is based on the generation of higher-order FM sidebands by an intracavity phase modulator and the periodic selection of the sidebands by an intracavity high-finesse Fabry–Perot filter at spacings of free spectral range which is a harmonic of the modulation frequency. We show the generation of stable, uniformly spaced, equal amplitude optical pulses from a fiber ring laser with two-, three-, and fourfold enhancement in the repetition rate. © 1998 American Institute of Physics.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Wd Fiber lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Ci Filters, zone plates, and polarizers

High-finesse disk microcavity based on a circular Bragg reflector

D. Labilloy, H. Benisty, C. Weisbuch, T. F. Krauss, C. J. M. Smith, R. Houdré, and U. Oesterle

Appl. Phys. Lett. 73, 1314 (1998); http://dx.doi.org/10.1063/1.121880 (3 pages) | Cited 35 times

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We made disk-shaped microcavities of approximately 10 μm2 in area in a GaAs/AlGaAs waveguide structure by etching deep vertical concentric trenches. The trenches form a circular Bragg-like reflector that confines light in the remaining two lateral dimensions. We demonstrate from photoluminescence excited in the waveguide the confinement of discrete disk modes whose wave vector is mainly radial, in contrast with whispering gallery modes. Their quality factors up to Q = 650 indicate in-plane reflectivities approaching 90%. In the near infrared, this represents a demonstration of wavelength-scale light confinement based on photonic crystal effects in two dimensions. © 1998 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.65.Cf Surface cleaning, etching, patterning
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
42.50.-p Quantum optics

Photogeneration and modification of birefringence in crosslinked films of liquid crystal/polymer composites

Shin’ya Morino, Aki Kaiho, and Kunihiro Ichimura

Appl. Phys. Lett. 73, 1317 (1998); http://dx.doi.org/10.1063/1.121881 (3 pages) | Cited 7 times

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A binary composite consisting of a low-mass nematic liquid crystal and a crosslinked polymer bearing azobenzene chromophores exhibited thermally stable birefringence upon linearly polarized light irradiation owing to the angular-selective photoexcitation of the chromophores. The extent of photoinduced birefringence was critically dependent on temperatures during the photoirradiation. The largest photoinduced birefringence of 0.05 was obtained at 75 °C—slightly lower than TNI of the liquid crystal. The photogenerated birefringence was overwritten on linearly polarized light irradiation. © 1998 American Institute of Physics.  
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78.66.Qn Polymers; organic compounds
42.25.Lc Birefringence
78.20.Fm Birefringence
42.70.Df Liquid crystals
61.30.-v Liquid crystals

Accurate measurement of laser-driven shock trajectories with velocity interferometry

P. M. Celliers, G. W. Collins, L. B. Da Silva, D. M. Gold, and R. Cauble

Appl. Phys. Lett. 73, 1320 (1998); http://dx.doi.org/10.1063/1.121882 (3 pages) | Cited 60 times

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We describe a velocity interferometer used to measure the velocity and trajectory of laser driven shocks in liquid deuterium accurately and continuously. This demonstration of velocity interferometry to measure shock velocity and shock trajectory in condensed matter shows strong potential for future studies of laser-driven shocks in transparent media. Accuracy of this technique can be better than 1% in velocity and ±0.2 μm in position during a 10 ns interval. © 1998 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
07.60.Ly Interferometers
06.30.Gv Velocity, acceleration, and rotation
06.60.Jn High-speed techniques (microsecond to femtosecond)
07.68.+m Photography, photographic instruments; xerography
62.10.+s Mechanical properties of liquids

Optical data storage in C60 doped polystyrene film by photo-oxidation

A. D. Xia, S. Wada, and H. Tashiro

Appl. Phys. Lett. 73, 1323 (1998); http://dx.doi.org/10.1063/1.121883 (3 pages) | Cited 15 times

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A potential application of C60 for three-dimensional optical data storage in read only memory recorded by photo-oxidation is investigated. Photo-oxidation significantly enhances the fluorescence intensity of C60 molecules; therefore, one bit data can be recorded by the photo-oxidation of C60 doped polystyrene film at individual points by a focused laser beam and be read nondestructively as a brilliant fluorescence spot, in contrast to the nonoxidized areas after photo-oxidation is blocked. This enables three-dimensional recording using a laser scanning microscope. As a result, a pattern consisting of three layers of bit data was written and read in a C60 doped polystyrene film. We also discuss the time course of photo-oxidation of C60. © 1998 American Institute of Physics.
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78.55.Kz Solid organic materials
81.65.Mq Oxidation
42.79.Vb Optical storage systems, optical disks
61.41.+e Polymers, elastomers, and plastics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
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The electrorheological behavior of complex strontium titanate suspensions

Yuling Zhang, Yong Ma, Yucheng Lan, Kunquan Lu, and Wei Liu

Appl. Phys. Lett. 73, 1326 (1998); http://dx.doi.org/10.1063/1.121884 (3 pages) | Cited 10 times

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A type of water-free electrorheological (ER) material-complex strontium titanate (STO) was synthesized by means of modified sol–gel. The ER behavior of the suspensions of STO particles in silicone oil with a 37% volume fraction was investigated systematically under both dc and ac electric fields. It is found that this ER fluid has many advantages, such as long-term stability against sedimentation, strong ER effect at low electric field, and a wide operating temperature range. The frequency dependence of ER behavior was also studied and can be partly explained on the basis of dielectric measurement. © 1998 American Institute of Physics.  
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83.80.-k Material type
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
82.70.Kj Emulsions and suspensions
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.80.Iz Emulsions and foams

Self-similarity of fluid flows

Liqiu Wang

Appl. Phys. Lett. 73, 1329 (1998); http://dx.doi.org/10.1063/1.121885 (2 pages)

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Relations among flows at different scales are developed through examining flow response to multiplicative changes of spatial and temporal scales. The scaling invariance of physical definitions leads to the self-similarity of flows and the scaling invariance of fundamental laws governing the flows. Also developed is both the necessary and sufficient condition for a physical quantity to be self-similar, which forms a general function dependence of any self-similar quantity on position and time. © 1998 American Institute of Physics.
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47.10.-g General theory in fluid dynamics
47.11.-j Computational methods in fluid dynamics

Breakdown of equilibrium approximation for nanosecond laser-induced electron emission from silicon

Samual S. Mao, Xianglei Mao, Ralph Greif, and Richard E. Russo

Appl. Phys. Lett. 73, 1331 (1998); http://dx.doi.org/10.1063/1.121886 (3 pages) | Cited 2 times

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We demonstrate that nonequilibrium carrier dynamics play a significant role in nanosecond laser-induced electron emission from semiconductor surfaces. Surface emission current and electron yields due to thermionic and photoelectric effects are calculated for a 2 ns laser pulse irradiation, with fluences below the threshold for melting. The photoelectric effect is found to dominate electron emission only at low fluences, whereas thermionic emission from interband absorption is responsible for electron emission at high incident fluences. The results present a satisfactory interpretation of experimental observations for nanosecond laser-induced electron emission from silicon. © 1998 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.40.+z Thermionic emission

X-ray emission from metallic (Al) and dielectric (glass) targets irradiated by intense ultrashort laser pulses

A. Saemann and K. Eidmann

Appl. Phys. Lett. 73, 1334 (1998); http://dx.doi.org/10.1063/1.121887 (3 pages) | Cited 8 times

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We measured in a large spectral range from 180 eV to 20 keV the x-ray emission from aluminum and glass targets irradiated by 150 fs laser pulses at intensities of ≈ 1017 W/cm2. Unexpected large differences are observed at photon energies above ≈ 1 keV, where the Al target emitted almost 100 times more x rays than glass. Important for this result is a high prepulse to main pulse contrast. © 1998 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
28.52.Cx Fueling, heating and ignition
52.70.La X-ray and γ-ray measurements
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Temperature-induced changes in photopolymer volume holograms

Lisa Dhar, Melinda G. Schnoes, Theresa L. Wysocki, Harvey Bair, Marcia Schilling, and Carol Boyd

Appl. Phys. Lett. 73, 1337 (1998); http://dx.doi.org/10.1063/1.122375 (3 pages) | Cited 49 times

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Temperature-induced distortions of plane-wave holographic gratings recorded in low glass transition temperature (Tg ∼ 26 °C) photopolymer media were measured. Changes in temperature affect the refractive index and dimensions of photopolymer materials, thereby rotating the angular Bragg selectivity of recorded volume holograms. From temperature-dependent measurements on a set of angularly multiplexed holograms, the out-of-plane coefficient of thermal expansion of a thin photopolymer film constrained between two rigid glass substrates is found to be 500 ppm/°C. These experiments suggest that the temperature sensitivity of photopolymer volume holograms may limit their use in many applications. © 1998 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
68.60.Dv Thermal stability; thermal effects
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.79.Wc Optical coatings
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
65.40.De Thermal expansion; thermomechanical effects

Atomic force microscopy studies of ZnSe self-organized dots fabricated on ZnS/GaP

Z. H. Ma, W. D. Sun, I. K. Sou, and G. K. L. Wong

Appl. Phys. Lett. 73, 1340 (1998); http://dx.doi.org/10.1063/1.122156 (3 pages) | Cited 10 times

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ZnSe self-organized dot structures on ZnS thin films were fabricated by the molecular beam epitaxy technique. In situ reflection high-energy electron diffraction studies reveal that growth interruption is required for the formation of the dot structure. Atomic force microscopy (AFM) images of the dots taken within the same day of growth reveal that the dot density increases with increasing ZnSe coverage. A density of 18 μm−2 was achieved with a coverage of 8.0 ZnSe monolayers. AFM images taken at later times (up to six months later) show ripening effects. The average dot size measured at various times after growth is consistent with the prediction of the Ostwald ripening model with a growth time constant of 4±1 days for the structure with a coverage of 8.0 ZnSe monolayers. The dot size and density in the fully ripened state are essentially independent of the initial ZnSe coverage. © 1998 American Institute of Physics.
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81.05.Dz II-VI semiconductors
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
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ga II-VI semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

On the nature of nanometer-scale islands formed by cadmium selenide deposition on hexagonal cadmium sulfide (0001)A

M. Grün, F. Funfrock, P. Schunk, Th. Schimmel, M. Hetterich, and C. Klingshirn

Appl. Phys. Lett. 73, 1343 (1998); http://dx.doi.org/10.1063/1.122157 (3 pages) | Cited 14 times

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Using ex situ atomic force microscopy, nanometer-scale islands were observed on CdS(0001)A surfaces to appear after deposition of small amounts of CdSe. The sizes of these islands are similar to those reported in atomic force microscopy (AFM) studies of uncapped CdSe/ZnSe structures. Investigations by force modulation microscopy and photoluminescence spectroscopy show, however, that they are difficult to assign to a CdSe Stranski–Krastanow growth. Instead, AFM points to an onset of the island formation with the exposure of the samples to atmosphere. By use of electron microprobe analysis, it is suggested that these islands consist of selenium. © 1998 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Electron affinity at aluminum nitride surfaces

C. I. Wu, A. Kahn, E. S. Hellman, and D. N. E. Buchanan

Appl. Phys. Lett. 73, 1346 (1998); http://dx.doi.org/10.1063/1.122158 (3 pages) | Cited 38 times

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We investigate the electron affinity of aluminum nitride surfaces prepared by nitrogen sputtering and annealing via x-ray, ultraviolet, and inverse photoemission spectroscopy. The combination of these techniques leads to a precise determination of the relative positions of the Fermi level, valence-band maximum, conduction-band minimum, and vacuum level at the semiconductor surface. We demonstrate that, in spite of the presence of a sharp photoemission onset feature previously associated with negative electron affinity, the electron affinity is clearly positive on these surfaces. © 1998 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.At Surface states, band structure, electron density of states
78.70.-g Interactions of particles and radiation with matter

Solid phase epitaxial regrowth of ion beam-amorphized α-quartz

F. Roccaforte, W. Bolse, and K. P. Lieb

Appl. Phys. Lett. 73, 1349 (1998); http://dx.doi.org/10.1063/1.122159 (3 pages) | Cited 17 times

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Solid phase epitaxial growth of ion beam-amorphized α-quartz has been studied by means of Rutherford backscattering spectrometry in channeling geometry. α-quartz single crystals were irradiated with Cs+ and Xe+ ions and annealed in air or in vacuum at 500–900 °C. Complete epitaxial regrowth has been observed in the Cs-irradiated samples, after 875 °C annealing in air. On the other hand, vacuum annealing provided only incomplete regrowth of the amorphous layer, while Xe-irradiated α-quartz could not be regrown up to 900 °C. The behavior of Cs in the recrystallization process is discussed in terms of the SiO2-network topology. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Np Solid phase epitaxy; growth from solid phases
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Ms Insulators

High-temperature phase transformation in Ti-diffused waveguide layers of LiNbO3

E. Zolotoyabko, Y. Avrahami, W. Sauer, T. H. Metzger, and J. Peisl

Appl. Phys. Lett. 73, 1352 (1998); http://dx.doi.org/10.1063/1.122160 (3 pages) | Cited 14 times

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Phase formation processes accompanying high-temperature Ti diffusion in thin waveguide layers of LiNbO3 were studied by grazing-incidence x-ray diffraction and complementary techniques. The development and decay of a rutilelike phase (Li0.25Nb0.75O2)1−x (TiO2)x was directly observed as a function of annealing time. A solid-state reaction is proposed, which clarifies the mechanism of phase transformation, relating it to cation replacements. © 1998 American Institute of Physics.
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77.80.B- Phase transitions and Curie point
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Interfacial reactions of Pd/Si0.76Ge0.24 by pulsed KrF laser annealing

Da-Ren Chen, Jian-Shing Luo, Wen-Tai Lin, C. Y. Chang, and P. S. Shih

Appl. Phys. Lett. 73, 1355 (1998); http://dx.doi.org/10.1063/1.122161 (3 pages) | Cited 10 times

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The interfacial reactions of Pd/Si0.76Ge0.24 were studied by pulsed KrF laser annealing as a function of energy density and pulse number. At an energy density of 0.1–0.4 J/cm2, a continuous germanosilicide layer composed of a low-temperature phase, Pd2(Si1−xGex), and a high-temperature phase, Pd(Si1−xGex), was formed. In contrast to vacuum annealing, Ge segregation out of the germanosilicide layer and the strain relaxation of the residual Si0.76Ge0.24 film could be effectively suppressed by pulsed KrF laser annealing at 0.1 J/cm2. Multiple pulse annealing at 0.1 J/cm2 could further homogenize the Pd concentration of the germanosilicide layer and promote the growth of Pd(Si1−xGex). Concurrently, the smoothness of the germanosilicide layer was substantially improved in comparison with those grown by vacuum annealing at temperatures above 200 °C. The studies also revealed that for multiple pulse annealing at 0.1 J/cm2 with a low repetition rate, 1 Hz, the evolution of phase formation and Pd diffusion could be proceeded by each individual laser pulse. © 1998 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.35.Fx Diffusion; interface formation

Optical modulation of bulk one-phonon state in diamond

Y. Mita, H. Kanehara, Y. Adachi, Y. Nisida, M. Okada, and M. Kobayashi

Appl. Phys. Lett. 73, 1358 (1998); http://dx.doi.org/10.1063/1.122162 (3 pages) | Cited 2 times

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Infrared absorption and electron spin resonance measurements have been performed in nitrogen-containing mixed-type diamonds under several illumination conditions. It has been observed that bulk one-phonon absorption spectra are modulated by illumination of higher than 2.0 eV in photon energy and the change recovers within a few hours after the excitation light is turned off. The results are explained by the change in the charge state of isolated nitrogen, and a characteristic absorption band created by the positive charge state of isolated nitrogen (N+) is proposed. This phenomenon is applicable in decomposing the infrared absorption spectra of diamonds into each component, which contain information about the type and concentration of nitrogen aggregate. © 1998 American Institute of Physics.
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78.40.Fy Semiconductors
78.30.Am Elemental semiconductors and insulators
42.79.Hp Optical processors, correlators, and modulators
76.30.Lh Other ions and impurities

Cold-field-emission test of the fatigued state of Pb(ZrxTi1−x)O3films

I. Stolichnov, A. K. Tagantsev, E. L. Colla, and N. Setter

Appl. Phys. Lett. 73, 1361 (1998); http://dx.doi.org/10.1063/1.122374 (3 pages) | Cited 34 times

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Fatigue phenomena occurring in Pb(ZrxTi1−x)O3 ferroelectric thin-film capacitors (FECAP) with Pt electrodes are studied by means of conduction measurements in the cold-field-emission (tunneling) regime. We have determined that conduction in virgin FECAPs is controlled by tunneling at temperatures 100–140 K and electric fields (2.3–3.0 MV/cm). The Fowler–Nordheim equation successfully describes observed current–voltage relations for reasonable values of the semiconductor parameters of the system. Fatigue of the switching polarization induced by bipolar voltage cycling provokes a substantial increase in tunneling conduction, shifting the I–V curve to lower fields by some 0.5 MV/cm. The partial restoration of the switching polarization produced by heating of the sample up to 490 K results in a complete restoration of the initial current–voltage characteristic. It is shown that the fatigue-induced increase in conduction can be modeled by the charging of an interfacial layer of a thickness comparable with the tunneling length. This interpretation is consistent with a fatigue scenario related to the space-charge-assisted blocking of near-by-electrode centers of domain nucleation. © 1998 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
79.70.+q Field emission, ionization, evaporation, and desorption
84.32.Tt Capacitors
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis

Transverse thermoelectric response of a tilted metallic multilayer structure

Th. Zahner, R. Förg, and H. Lengfellner

Appl. Phys. Lett. 73, 1364 (1998); http://dx.doi.org/10.1063/1.122376 (3 pages) | Cited 16 times

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Thermoelectric fields transverse to an applied temperature gradient have been observed in artificially created tilted multilayer structures. Copper-constantan multilayer structures were prepared by sintering of a compressed stack of copper/constantan/copper foils and by cutting the stack obliquely to its axis. Tilted multilayer structures represent a new class of thermoelectric devices, and applications for detection of light are demonstrated. © 1998 American Institute of Physics.
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72.15.Jf Thermoelectric and thermomagnetic effects
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.40.Jn Metal-to-metal contacts

Sb mediated C60 thin film growth on mica

Wentao Xu, J. G. Hou, and Z. Q. Wu

Appl. Phys. Lett. 73, 1367 (1998); http://dx.doi.org/10.1063/1.122163 (3 pages) | Cited 3 times

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We studied the growth of C60 thin films on a layer of surfactant Sb which was predeposited on mica substrates with vacuum vapor deposition method. It was found that the growth behaviors of C60 films are significantly affected by the surfactant Sb and the substrate temperature. (112)- and (111)-oriented C60 single-crystal films with large C60 single crystals were obtained when the substrate temperatures were 200 and 215 °C, respectively. The growth mechanisms of the Sb mediated C60 films were attributed to the reduced surface diffusion rate of adsorbed C60 molecules and the lowered boundary potential energy of C60 islands by surfactant Sb. © 1998 American Institute of Physics.
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81.05.ub Fullerenes and related materials
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Fx Diffusion; interface formation
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
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“S-shaped” temperature-dependent emission shift and carrier dynamics in InGaN/GaN multiple quantum wells

Yong-Hoon Cho, G. H. Gainer, A. J. Fischer, J. J. Song, S. Keller, U. K. Mishra, and S. P. DenBaars

Appl. Phys. Lett. 73, 1370 (1998); http://dx.doi.org/10.1063/1.122164 (3 pages) | Cited 244 times

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We report temperature-dependent time-integrated and time-resolved photoluminescence (PL) studies of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous emission behavior, specifically an S-shaped (decrease–increase–decrease) temperature dependence of the peak energy (Ep) for InGaN-related PL with increasing temperature: Ep redshifts in the temperature range of 10–70 K, blueshifts for 70–150 K, and redshifts again for 150–300 K with increasing temperature. In addition, when Ep redshifts, the spectral width is observed to narrow, while when Ep blueshifts, it broadens. From a study of the integrated PL intensity as a function of temperature, it is found that thermionic emission of photocarriers out of local potential minima into higher energy states within the wells is the dominant mechanism leading to the thermal quenching of the InGaN-related PL. We demonstrate that the temperature-induced S-shaped PL shift is caused by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the InGaN/GaN MQWs. © 1998 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
79.40.+z Thermionic emission
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Open-volume defect tails in Ge-implanted Si probed by slow positrons

A. P. Knights, A. Nejim, P. G. Coleman, H. Kheyrandish, and S. Romani

Appl. Phys. Lett. 73, 1373 (1998); http://dx.doi.org/10.1063/1.122165 (3 pages) | Cited 3 times

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Positron annihilation spectroscopy has been used in conjunction with anodic oxidation and etching to profile the distribution of open-volume defects beyond the range of 120 keV Ge ions implanted into (100) Si at a dose of 1×1014 cm−2. For a time-averaged dose rate (Jt) of 0.02 μA/cm−2 and incident angle of 7°, open-volume defects are found to exist at concentrations exceeding 1016 cm−3 at depths up to 600 nm, whereas the peak of the depth distribution of the implanted Ge ions (Rp) is 76 nm, measured using secondary ion mass spectroscopy. An increase in the depth of the defects observed when the implant is intentionally channeled on the 〈100〉 axis is thought to be simply correlated with a corresponding increase in Rp to 79 nm. When the time-averaged current is increased by a factor of 10 (incident angle=7°), defects persist at concentrations in excess of 1017 cm−3 beyond 1 μm and the Rp increases to 101 nm; this extended tail is attributed primarily to increased defect diffusion. © 1998 American Institute of Physics.
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78.70.Bj Positron annihilation
61.72.uf Ge and Si
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
61.72.-y Defects and impurities in crystals; microstructure
61.80.Jh Ion radiation effects

Spectra analysis of annealed Hg1−xCdxTe molecular beam epitaxial films

Biao Li, Yan Wu, Yongsheng Gui, Hongjuan Ye, Yong Chang, Li He, and Junhao Chu

Appl. Phys. Lett. 73, 1376 (1998); http://dx.doi.org/10.1063/1.122377 (3 pages) | Cited 2 times

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This letter discusses the analysis of infrared and visible spectra of Hg1−xCdxTe thin films deposited by molecular beam epitaxy (MBE) onto a CdTe buffer layer on a GaAs substrate. The spectra were obtained by infrared transmission and spectroscopic ellipsometry. Two mathematical techniques, fast Fourier transform (FFT) of the multiple reflectance spectrum associated with a multilayer system and fractional-derivatives spectra (FDS) were employed. Compared to the conventional fitting procedure, the FFT method directly offers the thickness of individual layers. It can also provide insight into the interfaces. The FDS method, however, gives information of composition and lattice perfection, which is useful in in situ real-time monitoring during the MBE run. The results show that annealing increases the compositional grading of Hg1−xCdxTe MBE films. Furthermore, the crystal microstructure deteriorates due to the irregular arrangement of diffusing atoms in the lattice sites. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors

Modulation-doped Cd1−xMnxTe/Cd1−yMgyTe quantum well structures with spatial in-plane profiling of the well width and the doping intensity

T. Wojtowicz, M. Kutrowski, G. Karczewski, and J. Kossut

Appl. Phys. Lett. 73, 1379 (1998); http://dx.doi.org/10.1063/1.122166 (3 pages) | Cited 38 times

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We report on the design and growth by molecular beam epitaxy of two types of graded Cd1−xMnxTe/Cd1−yMgyTe quantum well structures having a precisely controlled spatial profile of either the quantum well width and/or of the number of donors in one of the directions perpendicular to the growth axis. The existence of a spatially varying quantum well width was demonstrated by different wavelengths of the photoluminesce emitted from different regions of the sample. The presence of two-dimensional electron gas with a spatially varying concentration produced by graded modulation doping was evidenced by magneto-optical studies which revealed signatures of either excitons, or negatively charged exciton–electron complexes (X−), or Fermi-edge singularity, all in a single sample grown in one molecular beam epitaxy process. Such structures may be very useful for tunable wavelength radiation sources as well as in detailed studies of various physical characteristics of the quantum wells. © 1998 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ga II-VI semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.35.-y Excitons and related phenomena
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Observation of the phase inversion in photoreflectance spectra from ZnSe/GaAs(001) heterostructures

J. H. Song, E. D. Sim, S. H. Lee, and S. K. Chang

Appl. Phys. Lett. 73, 1382 (1998); http://dx.doi.org/10.1063/1.122167 (3 pages) | Cited 6 times

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The pump photon energy dependence of photoreflectance (PR) of a ZnSe/GaAs heterostructure has been measured at 77 K. The phase inversion in the PR signal is observed for the pump photon energy when it decreases from above to below the excitonic absorption edge of ZnSe. The observation of the phase inversion in PR is explained in terms of the modulation of the built-in electric field at the interface of the ZnSe/GaAs heterojunction, not at the ZnSe surface. It provides evidence of a built-in triangular-well potential and of hole traps at the ZnSe/GaAs interface. This argument is confirmed by photoreflectance excitation spectroscopy. © 1998 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.-e Optical properties of bulk materials and thin films
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Eq III-V semiconductors
71.55.Gs II-VI semiconductors
78.66.Fd III-V semiconductors
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