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9 Sep 1996

Volume 69, Issue 11, pp. 1503-1648

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Dynamic response of electro‐optic effect in free‐standing ferroelectric liquid crystal film

Sadahito Uto, Hideyo Ohtsuki, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 69, 1503 (1996); http://dx.doi.org/10.1063/1.117985 (3 pages) | Cited 9 times

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A study of an electro‐optic response in a free‐standing ferroelectric liquid crystal film has been carried out. The response time becomes shorter with increasing electric field and, especially at a certain threshold of electric field, it changes in stepwise by three orders of magnitude. The response time of the faster kind of response that appears in the higher field region is several hundred milliseconds and is about one thousand times faster than the slower kind of response at lower fields. © 1996 American Institute of Physics.
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42.70.Df Liquid crystals
78.20.Jq Electro-optical effects
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals

Light emission from germanium nanoparticles formed by ultraviolet assisted oxidation of silicon‐germanium

Valentin Craciun, Chantal Boulmer‐Leborgne, Edward J. Nicholls, and Ian W. Boyd

Appl. Phys. Lett. 69, 1506 (1996); http://dx.doi.org/10.1063/1.117986 (3 pages) | Cited 35 times

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Nanocrystalline Ge particles embedded in a SiO2 layer, directly formed by an excision process from a SiGe strained layer during low temperature ultraviolet‐assisted oxidation are shown to exhibit visible photoluminescence. The emission maxima of the photoluminescence spectra are situated at around 2.18 eV, a value that corresponds, according to recent data to an average particle size of 5 nm, in excellent agreement with our previous Raman and transmission electron microscopy measurements of particle size. It is proposed that stress effects associated with the oxidation of small spherical particles allow the formed nanocrystalline Ge to survive during prolonged ultraviolet oxidation of the SiGe layer. © 1996 American Institute of Physics.
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78.66.Vs Fine-particle systems
78.55.Ap Elemental semiconductors
81.65.Mq Oxidation

Influence of light on the coercive field of repoled strontium barium niobate: The role of secondary repoling

Peter G. R. Smith and Robert W. Eason

Appl. Phys. Lett. 69, 1509 (1996); http://dx.doi.org/10.1063/1.117987 (3 pages) | Cited 6 times

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We have found that the application of light to strontium barium niobate (SBN) during electrical repoling stabilizes the newly formed domains. This stabilization becomes apparent when repoling the crystal back into its original domain direction as a change in the distribution of displacement current as a function of voltage. This appears to be the process underlying the other recent work in the area of optical control of domain structures for quasi‐phase‐matching of nonlinear processes. We present an explanation for this effect in terms of the microdomain structure of SBN. This model should aid in the search for new materials for optical periodic poling. © 1996 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Excitonic optical properties in fractional‐layer‐superlattice wire structures

Hiroaki Ando, Hisao Saito, Arturo Chavez‐Pirson, Hideki Gotoh, and Naoki Kobayashi

Appl. Phys. Lett. 69, 1512 (1996); http://dx.doi.org/10.1063/1.117988 (3 pages) | Cited 2 times

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We report on the evolution of the excitonic optical features from two dimensions (2D) to one dimension (1D) in GaAs/AlAs fractional‐layer‐superlattice (FLS) wire structures. We demonstrate for the first time how the excitonic optical properties continuously evolve from 2D to 1D by introducing the FLS lateral compositional modulation in an AlGaAs quantum well. We also present a theory numerically analyzing the optical absorption properties in the FLS wires. Present theory accurately reproduces the experimental results using the AlAs/GaAs FLS wires and clarifies the main optical features associated with excitons in the intermediate quantum‐confinement regime between 1D and 2D. © 1996 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.66.Fd III-V semiconductors

Frequency‐stable, narrow linewidth oscillation of red diode laser with phase‐conjugate feedback using stimulated photorefractive backscattering

Akira Shiratori and Minoru Obara

Appl. Phys. Lett. 69, 1515 (1996); http://dx.doi.org/10.1063/1.117989 (2 pages) | Cited 6 times

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Frequency‐stable, narrow linewidth oscillation of a 638 nm AlGaInP diode laser has been achieved with an external photorefractive BaTiO3 phase conjugator in a novel configuration. The mechanism of the phase conjugation in this configuration is the stimulated photorefractive backscattering process with the measured phase‐conjugate reflectivity of <1.8×10−3%. With this new phase‐conjugate feedback method, the laser linewidth was reduced to ∼0.1 nm (within the resolution limit of the spectrum analyzer used) and the oscillation frequency was highly stabilized, while it was impossible with a conventional cat conjugator. © 1996 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.55.Px Semiconductor lasers; laser diodes
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Intracavity spectroscopy in vertical cavity surface‐emitting lasers for micro‐optical‐mechanical systems

K. E. Meissner, P. L. Gourley, T. M. Brennan, B. E. Hammons, and A. E. McDonald

Appl. Phys. Lett. 69, 1517 (1996); http://dx.doi.org/10.1063/1.117990 (3 pages) | Cited 4 times

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We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface‐emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 μm) structures, and is well suited for use in micro‐optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single‐mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.
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42.55.Sa Microcavity and microdisk lasers
78.66.Vs Fine-particle systems

Polymeric optical intensity modulator optimized in quasi‐single mode operation

Wol‐Yon Hwang and Jang‐Joo Kim

Appl. Phys. Lett. 69, 1520 (1996); http://dx.doi.org/10.1063/1.117991 (3 pages) | Cited 2 times

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An electro‐optic polymer intensity modulator designed in the heavily multimode region but operating as a quasi‐single mode waveguide has been demonstrated. The device relaxes much of the trade‐off relationship between the modulation voltage and coupling efficiency without the sacrifice of the modulation extinction ratio. The device poled at 1.5 MV/cm shows half‐wave voltage–length product of 7.2 V cm, modulation extinction ratio better than 20 dB, and mode diameters of about 4 and 9 μm in vertical and lateral directions, respectively. © 1996 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.82.Et Waveguides, couplers, and arrays
42.70.Jk Polymers and organics

Time‐resolved luminescence studies of heavily nitrogen doped ZnSe

C. Kothandaraman, I. Kuskovsky, G. F. Neumark, and R. M. Park

Appl. Phys. Lett. 69, 1523 (1996); http://dx.doi.org/10.1063/1.117992 (3 pages) | Cited 8 times

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Time‐resolved luminescence data from heavily nitrogen doped ZnSe (total N concentration exceeding mid‐1018/cm3) is presented. The luminescence exhibited a decay time and a rise time which increased with decreasing energy of observation. Furthermore, both the decay times and rise times decreased with increasing temperature. These observations are consistent with the following model: (i) a band of states is created due to fluctuations in the ionized impurity concentrations; (ii) a portion of the carriers captured by the shallower impurity states are transferred to deeper states prior to recombination. © 1996 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Light distribution measurements in absorbing materials by optical detection of laser‐induced stress waves

G. Paltauf, H. Schmidt‐Kloiber, and H. Guss

Appl. Phys. Lett. 69, 1526 (1996); http://dx.doi.org/10.1063/1.117993 (3 pages) | Cited 30 times

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A method for optimized generation and detection of thermoelastic stress waves for the measurement of tissue optical properties and structure is investigated. The stress waves are formed by short pulsed irradiation of an absorbing dye solution with a Q‐switched Nd:YAG laser at 532 nm. An optical transducer based on pressure‐induced reflectivity changes of a continuous laser beam at a glass‐water interface detects the stress wave in front of the irradiated sample surface. It is shown theoretically and experimentally that this kind of detector, where the active area is a small spot close to the irradiated surface, minimizes signal distortion due to acoustic diffraction. Comparisons of absorption coefficients measured acoustically and from optical transmission show a good agreement between the two methods. The high sensitivity of the detector (1.5 mV/bar) makes it possible to keep the temperature and pressure rise in the investigated target low, which enables in vivo applications of the optical transducer. © 1996 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
42.62.Be Biological and medical applications
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
87.64.-t Spectroscopic and microscopic techniques in biophysics and medical physics

Monolithic polycapillary focusing optics and their applications in microbeam x‐ray fluorescence

N. Gao, I. Yu. Ponomarev, Q. F. Xiao, W. M. Gibson, and D. A. Carpenter

Appl. Phys. Lett. 69, 1529 (1996); http://dx.doi.org/10.1063/1.117994 (3 pages) | Cited 16 times

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Monolithic polycapillary focusing optics can collect a large solid angle of x rays from a point source and form intense focused beams for microbeam x‐ray fluorescence (MXRF) analysis. Such an optic was tested and characterized in a MXRF setup. For the Cu Kα line, the measured focal spot size of the optic was 43 μm full width at half‐maximum (FWHM). With the 16 W microfocusing x‐ray source (50 μm×10 μm), the average Cu Kα intensities over the focal spot was measured to be 8.9×104 photons/s/μm2. When compared to a straight single channel capillary optic with approximately the same output beam size, an intensity gain of 44 was obtained. The optic was applied to the MXRF setup to analyze trace elements in various samples and a minimum detection limit (MDL) of about 2 pg was achieved for the transition elements (V, Cr, Mn, and Fe). The optic was also used to map the distributions of trace elements in various samples. © 1996 American Institute of Physics.
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41.50.+h X-ray beams and x-ray optics
07.85.-m X- and γ-ray instruments
78.70.En X-ray emission spectra and fluorescence

8 W continuous wave front‐facet power from broad‐waveguide Al‐free 980 nm diode lasers

L. J. Mawst, A. Bhattacharya, J. Lopez, D. Botez, D. Z. Garbuzov, L. DeMarco, J. C. Connolly, M. Jansen, F. Fang, and R. F. Nabiev

Appl. Phys. Lett. 69, 1532 (1996); http://dx.doi.org/10.1063/1.117995 (3 pages) | Cited 69 times

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Al‐free 980 nm InGaAs/InGaAsP/InGaP laser structures grown by low‐pressure metalorganic chemical vapor deposition (LP‐MOCVD) have been optimized for high cw output power by incorporating a broad waveguide design. Increasing the optical‐confinement layer total thickness from 0.2 to 1.0 μm decreases the internal loss fivefold to 1.0–1.5 cm−1, and doubles the transverse spot size to 0.6 μm (full width half‐maximum). Consequently, 4‐mm long, 100‐μm‐aperture devices emit up to 8.1 W front‐facet cw power. cw power conversion efficiencies as high as 59% are obtained from 0.5‐mm long devices. Catastrophic‐optical‐mirror‐damage (COMD) power‐density levels reach 15.0–15.5 MW/cm2, and are found similar to those for InGaAs/AlGaAs facet‐coated diode lasers. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.60.Jb Light-emitting devices
78.66.Fd III-V semiconductors

Optimization of power extraction in a high‐power soliton fiber ring laser containing a chirped fiber grating

K. Tamura, T. Komukai, and M. Nakazawa

Appl. Phys. Lett. 69, 1535 (1996); http://dx.doi.org/10.1063/1.117996 (3 pages)

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Power extraction from a high‐power soliton fiber ring laser containing a chirped fiber grating is investigated with a variable output coupler. Comparisons are made between the intracavity pulse and the rejection port output pulse. It is shown that a good design for extracting high quality pulses at high power is to insert an intracavity filter to suppress spectral sideband generation and to take the output from the rejection port. The results should apply in general to soliton fiber lasers. Gain saturation is shown to be the main mechanism in the laser that compensates for changes in cavity loss. © 1996 American Institute of Physics.
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42.55.Wd Fiber lasers
42.81.Dp Propagation, scattering, and losses; solitons

High efficiency diode pumping of a saturable Bragg reflector‐mode‐locked Cr:LiSAF femtosecond laser

S. Tsuda, W. H. Knox, and S. T. Cundiff

Appl. Phys. Lett. 69, 1538 (1996); http://dx.doi.org/10.1063/1.117997 (3 pages) | Cited 11 times

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We pump a saturable Bragg reflector (SBR)‐mode‐locked Cr:LiSAF laser with a 0.5 W diffraction‐limited 670 nm laser diode and obtain average CW mode‐locked power of 100 mW of 70 fs pulses at λ=868 nm. The low loss of the SBR‐mode‐locking technique combined with a nearly diffraction limited pumping results in the highest optical conversion efficiency obtained with this type of laser to date. We discuss overall electrical efficiency of femtosecond lasers. © 1996 American Institute of Physics.
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42.55.Xi Diode-pumped lasers
42.60.Fc Modulation, tuning, and mode locking

In situ growth of optically active erbium doped Al2O3 thin films by pulsed laser deposition

R. Serna and C. N. Afonso

Appl. Phys. Lett. 69, 1541 (1996); http://dx.doi.org/10.1063/1.117998 (3 pages) | Cited 29 times

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Thin Al2O3 films are grown and in situ doped with erbium by pulsed laser deposition in a single step process, by alternate ablation from Al2O3 and Er targets. The as‐deposited films have an Er step dopant profile throughout the film thickness, whose concentration depends on the number of pulses at the Er target. The as‐grown films are optically active, as evidenced by the photoluminescence spectrum centered at 1.533 μm, corresponding to intra‐4f transitions in Er3+. The photoluminescence intensity increases upon annealing due to an increase of the luminescence lifetime. This is most likely a result of a decrease in the nonradiative decay channels, related to annealing of defects in the Al2O3 film. © 1996 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators
78.55.Hx Other solid inorganic materials

Evidence for acoustic waves induced by focused ion beams

Jochen Teichert, Lothar Bischoff, and Bernd Köhler

Appl. Phys. Lett. 69, 1544 (1996); http://dx.doi.org/10.1063/1.117999 (3 pages) | Cited 2 times

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Acoustic waves induced by an intensity modulated focused ion beam have been measured. The experiments were performed with Ga+ ions of 35 keV at a current of 3 nA and variable chopping frequency up to 10 MHz in a common focused ion beam system. The acoustic signals were detected by means of a piezoelectric sensor with integrated preamplifier. Frequency and position sensitivity of the sensor has been measured by laser excitation. Ion acoustic measurements have been carried out at the resonance frequencies of the sensor. A dependence on the sample material was found. The results show that the ion acoustic effect can be utilized for imaging and material analysis in focused ion beam systems. © 1996 American Institute of Physics.
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43.35.Yb Ultrasonic instrumentation and measurement techniques
07.64.+z Acoustic instruments and equipment
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing

Au49+, Pb50+, and Ta48+ ions from laser‐produced plasmas

E. Woryna, P. Parys, J. Wołowski, L. Láska, J. Krása, K. Mašek, M. Pfeifer, B. Králiková, J. Skála, P. Straka, and K. Rohlena

Appl. Phys. Lett. 69, 1547 (1996); http://dx.doi.org/10.1063/1.117057 (3 pages) | Cited 25 times

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Results of generation of intense currents of highly charged ions of heavy elements from laser‐produced Au, Pb, and Ta plasmas are reported. High‐power iodine laser PERUN operating with λ=1.315 μm was used for that purpose. Using a parabolic mirror with a hole in the center instead of a focusing lens increased the efficiency of the illumination system and made the ion measurements along the target normal possible. Multiply charged ions were recorded with an ion energy analyzer in a distance of 240 cm. © 1996 American Institute of Physics.
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52.25.Tx Emission, absorption, and scattering of particles
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.Nc Particle measurements

Axial extraction of high‐power microwaves from relativistic traveling wave amplifiers

S. A. Naqvi, G. S. Kerslick, J. A. Nation, and L. Schächter

Appl. Phys. Lett. 69, 1550 (1996); http://dx.doi.org/10.1063/1.117058 (3 pages) | Cited 4 times

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We report theoretical and experimental results from research into coaxial extraction of high‐power microwaves from X‐band traveling wave tube amplifiers. Power levels exceeding 60 MW have been measured at 9.1 GHz. The output level is relatively constant for the full 70 ns duration of the 700 kV, 500 A electron beam pulse. Results indicate that this coaxial geometry is broadband when compared to traditional, highly tuned radial extraction and may thus have applications in a range of high‐power microwave devices. © 1996 American Institute of Physics.
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41.75.Ht Relativistic electron and positron beams
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Az Waveguides, transmission lines, striplines

Laser induced stimulated emission for hydrogen atom density measurements in a hydrogen pulsed microwave discharge

L. Tomasini, A. Rousseau, G. Baravian, G. Gousset, and P. Leprince

Appl. Phys. Lett. 69, 1553 (1996); http://dx.doi.org/10.1063/1.117059 (3 pages) | Cited 10 times

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The laser induced stimulated emission (LISE) of the Balmer α line is used to measure the ground state hydrogen atom density in an efficient source of hydrogen atoms generated by a low‐pressure (1 Torr), pulsed microwave discharge at 2.45 GHz. The H atom kinetics in pure hydrogen discharges and in hydrogen–air mixture discharges are compared. It is shown that, for high atomic density and long plasma length crossing, the LISE Balmer α line is partially absorbed by the plasma. This provides an estimation of the H(n=2) atom density. © 1996 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges

Microstructure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts for n‐GaN

S. Ruvimov, Z. Liliental‐Weber, J. Washburn, K. J. Duxstad, E. E. Haller, Z.‐F. Fan, S. N. Mohammad, W. Kim, A. E. Botchkarev, and H. Morkoç

Appl. Phys. Lett. 69, 1556 (1996); http://dx.doi.org/10.1063/1.117060 (3 pages) | Cited 126 times

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Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts on n‐type GaN (∼1017 cm−3) epitaxial layers. The metals were deposited either by conventional electron‐beam or thermal evaporation techniques, and then thermally annealed at 900 °C for 30 s in a N2 atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112]TiN//[10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.35.Fx Diffusion; interface formation

Spectra investigation on Hall–Petch relationship in nanocrystalline Fe78Si9B13 alloy

Jian‐Min Li, Ming‐Xiu Quan, and Zhuang‐Qi Hu

Appl. Phys. Lett. 69, 1559 (1996); http://dx.doi.org/10.1063/1.117061 (3 pages) | Cited 4 times

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A complicated behavior was indicated in nanocrystalline Fe78Si9B13 alloy with grain size lower than 65 nm. No sign of dislocations after deformation has been found in nanocrystalline material, suggesting that it is unlikely that the dislocation pileup is involved. The reduction of the mean hyperfine field is attributed to a decrease in the number of nearest neighbor atoms on the grain boundaries, which may be responsible for the softening behavior in nanocrystalline material with an average crystallite size of 65 nm. An increasing peak of the phonon mode near 900 cm−1, reflecting strong electron–atom coupling in grain boundary of nanocrystalline material, was observed. © 1996 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Thermal resistance of thin diamond films deposited at low temperatures

H. Verhoeven, H. Rei\S, H.‐J. Fü\Ser, and R. Zachai

Appl. Phys. Lett. 69, 1562 (1996); http://dx.doi.org/10.1063/1.117062 (3 pages) | Cited 7 times

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The thermal resistance for conduction normal to diamond layers only a few microns thick, deposited at temperatures of about 500 °C on silicon using microwave‐plasma‐assisted chemical vapor deposition (MPACVD) and electron cyclotron resonance enhanced MPACVD, is measured using a specific laser‐heating method. A detailed analysis of the results obtained using this method allows the determination of the effective diamond–silicon boundary resistance and the resistance within the diamond layer independently of one another. The analysis shows that the effective boundary resistance is comparable to or even larger than the resistance within the thin diamond layers, and suggests that it depends on the grain dimensions at the interface. For grain sizes of 10 nm, an average effective boundary resistance of 2.4×10−7 m2 K/W is determined, whereas at 1.2×10−8 m2 K/W it is significantly lower for grains about an order of magnitude larger. The resistance within the diamond shows a similar qualitative behavior with respect to grain size. © 1996 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
81.05.ub Fullerenes and related materials

Domain inversion in ferroelectric MgO:LiNbO3 by applying electric fields

Atsuko Kuroda, Sunao Kurimura, and Yoshiaki Uesu

Appl. Phys. Lett. 69, 1565 (1996); http://dx.doi.org/10.1063/1.117031 (3 pages) | Cited 62 times

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An antiparallel ferroelectric domain in LiNbO3 doped with 5 mol % MgO (MgO:LN) was inverted at room temperature by applying a step‐like electric field. The lowest electric field was about one fifth of that for undoped LN, but a high field compared to that for BaTiO3 was found to be necessary from the analysis of the switching current. The long switching time (about 102 s under an electric field of 4.45 kV/mm) enabled us to observe the domain growth process in MgO:LN. The needle‐shaped nuclei grew into larger domains by nucleation on the existing domain wall, and the wall of the coalesced domain moved forward slowly. The process was similar to the domain reversal model proposed for BaTiO3 under low electric fields. © 1996 American Institute of Physics.
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77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Optical gain and carrier lifetime of InGaN multi‐quantum well structure laser diodes

Shuji Nakamura, Masayuki Senoh, Shin‐ichi Nagahama, Naruhito Iwasa, Takao Yamada, Toshio Matsushita, Yasunobu Sugimoto, and Hiroyuki Kiyoku

Appl. Phys. Lett. 69, 1568 (1996); http://dx.doi.org/10.1063/1.117032 (3 pages) | Cited 60 times

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InGaN multi‐quantum well (MQW) structure laser diodes (LDs) with various different cavity lengths were fabricated on sapphire substrates with (1120) orientation (A face). The external differential quantum efficiency was obtained as a function of the cavity length. An internal quantum efficiency of 86%, an intrinsic loss of 54 cm−1 and a threshold gain of 110 cm−1 were obtained. Measuring the pulse response of the LDs, a carrier lifetime of 2.5 ns was obtained. A threshold carrier density was calculated as 1.3×1019/cm3. The emission wavelength of the LDs was around 406 nm. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors

Photovoltaic effect in PbS/PbTiO3/Si heterostructures

L. Pintilie, M. Alexe, I. Pintilie, and T. Botila

Appl. Phys. Lett. 69, 1571 (1996); http://dx.doi.org/10.1063/1.117033 (3 pages) | Cited 7 times

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PbS/PbTiO3/Si heterostructures were prepared by successive depositions of a PbTiO3 thin film using the sol‐gel method and of a PbS thin film using the coprecipitation method on a bulk silicon wafer. The current–voltage characteristic of the heterostructure is of a diode type. The heterostructure is sensitive over a broad range of wavelengths, from 0.35 to 3 μm, when illuminated with continuous light or with modulated light. Three sensitivity peaks are observed, at 2.7, 0.95, and 0.38 μm. The measured signals are attributed to a photovoltaic effect which appears in the studied heterostructure.
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73.50.Pz Photoconduction and photovoltaic effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

High‐resolution x‐ray diffraction study of piezoelectric InGaAs/GaAs multiquantum well p‐i‐n photodiodes grown on (111)B GaAs

A. Sanz‐Hervás, M. Aguilar, J. L. Sánchez‐Rojas, A. Sacedón, E. Calleja, E. Muñoz, E. J. Abril, and M. López

Appl. Phys. Lett. 69, 1574 (1996); http://dx.doi.org/10.1063/1.117034 (3 pages) | Cited 7 times

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High‐resolution x‐ray diffractometry has been applied to the structural characterization of piezoelectric strained InGaAs/GaAs multiquantum well p‐i‐n diodes grown by molecular beam epitaxy on (111)B GaAs substrates. Reference samples simultaneously grown on (001) GaAs have been also characterized. Diodes with 3, 7, and 10 periods and different well to barrier thickness ratio have been studied. Symmetric and asymmetric reflections at various azimuths were measured and the scans were fitted with theoretical curves obtained through a dynamical simulation program developed in our lab. The comparison between experimental and simulated profiles has enabled us to determine the main structural parameters of the samples. High‐resolution x‐ray diffractometry provided accurate data about period and capping layer thicknesses, indium content in the wells and state of relaxation, information which cannot be always obtained in (111)B samples from other characterization techniques such as photoluminescence or photocurrent spectroscopies. © 1996 American Institute of Physics.
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61.05.C- X-ray diffraction and scattering
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.60.Bt Optoelectronic device characterization, design, and modeling
77.65.Ly Strain-induced piezoelectric fields
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