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1 Jun 1998

Volume 72, Issue 22, pp. 2779-2913

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Near-field scanning solid immersion microscope

L. P. Ghislain and V. B. Elings

Appl. Phys. Lett. 72, 2779 (1998); http://dx.doi.org/10.1063/1.121457 (3 pages) | Cited 25 times

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We report a near-field scanning optical microscope using a solid immersion lens having a sharp tip that is mounted to a cantilever. The sharp tip allows the sample to enter the near field of the illumination. The cantilever provides sensitive control of forces. We describe two types of near-field optical contrast, interference and reflection, that simultaneously measure surface topography and reflectivity. Using a super-hemispherical lens with index n = 2.2 and 442 nm illumination, the microscope resolves optical features smaller than 150 nm, a factor of 2 improvement over a conventional optical microscope. © 1998 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes

Guiding and antiguiding effects in epitaxially regrown vertical-cavity surface-emitting lasers

T.-H. Oh, M. R. McDaniel, D. L. Huffaker, and D. G. Deppe

Appl. Phys. Lett. 72, 2782 (1998); http://dx.doi.org/10.1063/1.121458 (3 pages) | Cited 1 time

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The fabrication and optical mode characteristics of epitaxially regrown vertical-cavity surface-emitting lasers are presented. Modeling suggests that a highly resistive AlGaAs current blocking layer grown at low temperature by molecular beam epitaxy can be used to form an antiguiding structure, and antiguiding effects are observed in 10 μm diameter devices. Additional influence on the optical mode arises due to discontinuities associated with the etch and regrowth. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.66.Fd III-V semiconductors

Enhancement of x-ray lasing due to wavefront correction of line-focusing optics with a large-aperture deformable mirror

Geun-Young Yoon, Takeomi Imani, Hiroyuki Daido, Takahisa Jitsuno, Yoshiaki Kato, Masahiro Nakatsuka, Shiji Wang, Zunqi Lin, Yuan Gu, Guanlong Huang, Huajing Tang, and Guoping Zhang

Appl. Phys. Lett. 72, 2785 (1998); http://dx.doi.org/10.1063/1.121459 (3 pages) | Cited 5 times

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Intense x-ray laser radiation at 7.92 nm in nickel-like neodymium has been achieved by improving the line-focusing pattern using a large-aperture deformable mirror. A deformable mirror of 40 cm diameter with hexagonally arranged 37 mechanical actuators has been developed. The wavefront aberration due to a cylindrical lens used for line focusing has been corrected with the deformable mirror to produce a line-focusing pattern of uniform narrow width and uniform intensity distribution. The intensity of the x-ray laser beam has increased six times due to the improvement of the line-focusing pattern. © 1998 American Institute of Physics.
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42.60.By Design of specific laser systems
42.55.Vc X- and γ-ray lasers
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.79.Bh Lenses, prisms and mirrors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Enhanced nonlinear optical response of an endohedral metallofullerene through metal-to-cage charge transfer

J. R. Heflin, D. Marciu, C. Figura, S. Wang, P. Burbank, S. Stevenson, and H. C. Dorn

Appl. Phys. Lett. 72, 2788 (1998); http://dx.doi.org/10.1063/1.121456 (3 pages) | Cited 18 times

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A new mechanism for increasing the third-order nonlinear optical susceptibility, χ(3), is described for endohedral metallofullerenes. A two to three orders of magnitude increase in the nonlinear response is reported for degenerate four-wave mixing experiments conducted with solutions of Er2C82 (isomer III) relative to empty-cage fullerenes. A value of −8.7×10−32 esu is found for the molecular susceptibility, γxyyx, of Er2C82 compared to previously reported values of γxxxx = 3×10−34 esu and γxyyx = 4×10−35 esu for C60. The results confirm the importance of the metal-to-cage charge-transfer mechanism for enhancing the nonlinear optical response in endohedral metallofullerenes. © 1998 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Long pulse operation of an x-ray preionized molecular fluorine laser excited by a prepulse–main pulse system with a magnetic switch

H. M. J. Bastiaens, S. J. M. Peeters, X. Renard, P. J. M. Peters, and W. J. Witteman

Appl. Phys. Lett. 72, 2791 (1998); http://dx.doi.org/10.1063/1.121460 (3 pages) | Cited 3 times

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The application of a prepulse–main pulse excitation scheme utilizing a saturable magnetic switch in combination with x-ray preionization has resulted in the generation of long optical pulses from a molecular fluorine laser. Optimum laser pulse durations of 70 ns (full width half maximum) have been obtained in a gas mixture of helium and 3 mbar fluorine at a total pressure of 2 bar. The laser pulse duration is limited by instabilities in the discharge. The laser pulse duration is found to decrease with increasing fluorine pressure and to saturate with increasing current density. © 1998 American Institute of Physics.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers

Domain inversion by pulse poling in polymer films

V. Taggi, F. Michelotti, M. Bertolotti, G. Petrocco, V. Foglietti, A. Donval, E. Toussaere, and J. Zyss

Appl. Phys. Lett. 72, 2794 (1998); http://dx.doi.org/10.1063/1.121494 (3 pages) | Cited 4 times

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We report on an original technique for poling polymeric thin films, which allowed us to obtain a second-order nonlinear inverted domain structure, which could be used for frequency-doubling waveguides under quasi-phase-matching condition. Measurements of the local value and orientation of the electro-optic r33 tensor component were performed by a reflection microscopic electro-optic ellipsometer. The measured parameters for the nonlinear structure induced in the polymeric film result to be consistent with the expected values. © 1998 American Institute of Physics.
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77.22.Ej Polarization and depolarization
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
77.55.-g Dielectric thin films
42.82.Et Waveguides, couplers, and arrays
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.65.-k Nonlinear optics
77.84.Jd Polymers; organic compounds

Laser cleaning of field emitter arrays for enhanced electron emission

O. Yavas, N. Suzuki, M. Takai, A. Hosono, and S. Kawabuchi

Appl. Phys. Lett. 72, 2797 (1998); http://dx.doi.org/10.1063/1.121461 (3 pages) | Cited 17 times

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The effect of laser irradiation on the electron emission efficiency of field emitter arrays has been investigated as a function of wavelength using different harmonics of a diode-pumped Nd:YLF laser. While irradiation in the infrared or visible range did not induce any observable change in the emission behavior, ultraviolet laser irradiation, even at a lower fluence compared to infrared or visible, resulted in a significant increase of the emission efficiency, revealing that the photodecomposition of organic contaminants is the main mechanism for cleaning. During laser irradiation, the emission current increases gradually, approaching a saturation level as the surface is cleaned. © 1998 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
81.65.Cf Surface cleaning, etching, patterning
79.70.+q Field emission, ionization, evaporation, and desorption
42.62.-b Laser applications

Cavitation and acoustic emission around laser-heated microparticles

Charles P. Lin and Michael W. Kelly

Appl. Phys. Lett. 72, 2800 (1998); http://dx.doi.org/10.1063/1.121462 (3 pages) | Cited 51 times

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We studied transient cavitation bubble formation and acoustic emission around individual laser-heated microparticles using subnanosecond time-resolved microscopy. Microcavitation bubbles were observed as early as 0.5 ns after the particles were heated by a 30 ps laser pulse. The bubbles expanded to a few micrometers in size and collapsed on the time scale of 0.1–1 μsec. We discuss microcavitation as the origin of anomalously large photoacoustic effects and nonlinear optical responses observed in laser-heated colloidal suspensions, as well as a mechanism for cellular damage in biologic tissue containing pigment particles. © 1998 American Institute of Physics.  
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47.55.dp Cavitation and boiling
43.35.Ei Acoustic cavitation in liquids
62.65.+k Acoustical properties of solids
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
79.20.Ds Laser-beam impact phenomena
62.60.+v Acoustical properties of liquids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Quantitative determination of the local Kerr rotation by scanning near-field magneto-optic microscopy

P. Fumagalli, A. Rosenberger, G. Eggers, A. Münnemann, N. Held, and G. Güntherodt

Appl. Phys. Lett. 72, 2803 (1998); http://dx.doi.org/10.1063/1.121463 (3 pages) | Cited 27 times

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By using a polarization-modulation technique in combination with reflection-mode scanning near-field optical microscopy we are able to determine quantitatively the local polar Kerr rotation on thin magnetic films. As an example, the magneto-optic contrast of magnetic domains thermomagnetically written on a Co/Pt sample is discussed. The size of the magnetic domains is 3×0.5 μm2 and the angular resolution of the local Kerr rotation is better than 0.1°. This measurement technique will make it possible to investigate, e.g., the fine structure of domain walls by scanning near-field optical microscopy. © 1998 American Institute of Physics.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
07.79.Fc Near-field scanning optical microscopes

Dual-functional polymeric waveguide with optical amplification and electro-optic modulation

Dechang An, Zuzhou Yue, and Ray T. Chen

Appl. Phys. Lett. 72, 2806 (1998); http://dx.doi.org/10.1063/1.121464 (2 pages) | Cited 16 times

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Optical amplification and first-order electro-optic effect have been observed simultaneously in one polymeric material photolime gel which has been used widely as a volume holographic material to produce dichromated gelatin films. In this letter, the dual functions were achieved by doping neodymium chloride hexahydrate and chlorophenol red. The optimized doping concentration of Nd+3 is 6.7×1019 cm−3. The weight percentage of chlorophenol red is 23%. We observed a 3.8 dB of optical gain at 1.06 μm and an electro-optic coefficient of 22 pm/V at 633 nm. © 1998 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
42.79.Wc Optical coatings
78.20.Jq Electro-optical effects
42.82.Et Waveguides, couplers, and arrays
42.65.Wi Nonlinear waveguides
82.70.Gg Gels and sols
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.65.Yj Optical parametric oscillators and amplifiers
42.79.Hp Optical processors, correlators, and modulators

Gratinglike modulation of GaAs/AlGaAs quantum well intermixing fabricated with laser interference

Jaw-Jung Shin, Steffen Gurtler, Yih Chang, and C. C. Yang

Appl. Phys. Lett. 72, 2808 (1998); http://dx.doi.org/10.1063/1.121465 (3 pages) | Cited 2 times

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We report the observation of a μm range periodical modulation of a band gap caused by gratinglike quantum well intermixing in an intrinsic GaAs/AlGaAs quantum well structure. The intermixing grating was formed with the irradiation of the interference fringe of the second harmonic of a Q-switched Nd:YAG laser followed by a rapid thermal annealing process. The intermixing grating periods were measured with an optical setup for simultaneously monitoring the photoluminescence intensities of two closely spaced wavelengths with a sub-μm spatially scanning resolution. The measured periods included a cluster of features around 2 μm which was consistent with that of the laser interference fringe. © 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.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states
42.79.Dj Gratings

Cylindrical microlasers and light emitting devices from conducting polymers

S. V. Frolov, A. Fujii, D. Chinn, Z. V. Vardeny, K. Yoshino, and R. V. Gregory

Appl. Phys. Lett. 72, 2811 (1998); http://dx.doi.org/10.1063/1.121466 (3 pages) | Cited 59 times

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Substantially improved, photopumped polymer lasers are demonstrated using microrings and microdisks of various diameters D ranging from 5 to 200 μm. Various cavity-dependent laser modes were observed, which for D<10 μm were dominated by a single longitudinal mode with linewidth of less than 1 Å. These microlasers were also characterized by Q of order 5000, low threshold excitation energy of order 100 pJ/pulse for pulse duration ranging from 100 ps to sub-μs, and an abrupt increase in the emission directionality and polarization degree. Light emitting diodes with cylindrical geometry, fully compatible with these microlasers are also demonstrated. © 1998 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Jk Polymers and organics
85.60.Jb Light-emitting devices
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Hj Laser materials
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Influence of W via on the mechanism of electromigration failure in Al–0.5 Cu interconnects

H. A. Le, N. C. Tso, T. A. Rost, and C.-U. Kim

Appl. Phys. Lett. 72, 2814 (1998); http://dx.doi.org/10.1063/1.121467 (3 pages) | Cited 2 times

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This letter reports the effects of via current density on electromigration (EM) failure in Al–0.5 Cu conductors. Two-level metallization structures, differing in the number of feeding vias (1, 6, and 15), were made with the same pattern of Al lines at two levels to allow simultaneous EM testing of upper- and lower-level lines. It was established that the lower-level lines were more susceptible to the impact of the via, resulting in a failure by the formation of a local void beneath a via and a strong dependence of EM lifetime on the via current density. The results led to a phenomenological equation that incorporates via structure into failure kinetics. © 1998 American Institute of Physics.  
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Adsorption-controlled growth of Bi4Ti3O12 by reactive MBE

C. D. Theis, J. Yeh, D. G. Schlom, M. E. Hawley, G. W. Brown, J. C. Jiang, and X. Q. Pan

Appl. Phys. Lett. 72, 2817 (1998); http://dx.doi.org/10.1063/1.121468 (3 pages) | Cited 25 times

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Adsorption-controlled conditions have been identified and utilized to grow epitaxial bismuth titanate thin films by reactive molecular beam epitaxy. Growth of stoichiometric, phase pure, c-axis oriented, epitaxial films is achieved by supplying a large overabundance of bismuth and ozone continuously to the surface of the depositing film. Titanium is supplied to the film in the form of shuttered bursts each containing a three monolayer dose of titanium to grow one formula unit of Bi4Ti3O12. It is seen from measured film thickness, Rutherford backscattering spectrometry composition measurements, monitoring of reflection high-energy electron diffraction half-order intensity oscillations during growth, and in situ flux measurements using atomic absorption spectroscopy that at suitable temperature and ozone background pressure, the titanium sticking coefficient approaches one and the excess bismuth desorbs from the surface. Film growth proceeds by the formation of mounds whose step heights are predominantly integral multiples of a half-unit cell.© 1998 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)

Investigation of bulk and interfacial properties of Ba0.5Sr0.5TiO3 thin film capacitors

Sufi Zafar, Robert E. Jones, Peir Chu, Bruce White, Bo Jiang, Deborah Taylor, Peter Zurcher, and Sherry Gillepsie

Appl. Phys. Lett. 72, 2820 (1998); http://dx.doi.org/10.1063/1.121495 (3 pages) | Cited 54 times

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In this letter, we report the results for capacitance versus frequency measurements on a set of Ba0.5Sr0.5TiO3 (BST) capacitors with platinum electrodes (Pt) and varying BST film thicknesses. The study shows that Pt/BST interfacial capacitance is independent of frequency whereas the bulk dielectric constant has a power law dependence on frequency. Also, the bulk dielectric constant is observed to decrease whereas the interfacial capacitance increases with increasing temperature. In addition, we report the dependence of dielectric dispersion on BST film thickness and temperature. Calculations are performed which provide insights into the observed dispersion effects. © 1998 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
77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)

Crystallization of amorphous (Ba, Sr)TiO3/MgO(001) thin films

D. Y. Noh, H. H. Lee, T. S. Kang, and J. H. Je

Appl. Phys. Lett. 72, 2823 (1998); http://dx.doi.org/10.1063/1.121469 (3 pages) | Cited 11 times

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The crystallization of amorphous BaxSr1−xTiO3 (BST) thin films was studied in a synchrotron x-ray scattering experiment. In a 550 Å thick film, the crystallization to perovskite phase was occurred at around 700 °C, while a 5500 Å thick film became crystalline at 500 °C. The thickness dependence of the crystallization was attributed to the observed intermediate phase nucleated near 600 °C at the interface. In thin films, high annealing temperature was required due to the energy barrier between the perovskite phase and the intermediate phase. In the thick film, the perovskite phase was nucleated directly from the amorphous phase in the bulk of the film concurrent to the nucleation of the intermediate phase at the interface. © 1998 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.Er Other amorphous solids
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
78.70.Ck X-ray scattering

Phases of cobalt-iron ternary disilicides

I. Dézsi, Cs. Fetzer, I. Szucs, G. Langouche, and A. Vantomme

Appl. Phys. Lett. 72, 2826 (1998); http://dx.doi.org/10.1063/1.121470 (3 pages) | Cited 3 times

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Cobalt–iron transition-metal disilicides were investigated by Mössbauer effect and x-ray diffraction in order to determine the concentration range of their homogeneous and separate phase formation. Except at low Co or Fe concentrations, Co and Fe formed separate CoSi2 and FeSi2 phases. Up to 10 at % Co was found soluble in β-FeSi2; Fe dissolved in CoSi2 below 1.5 at % and was positioned at two different sites of cubic symmetry. The results obtained for the phase formation in thin layers of epitaxial CoSi2 on Si implanted with Fe were in agreement with the results obtained for the bulk samples. © 1998 American Institute of Physics.
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81.30.Dz Phase diagrams of other materials
61.66.Fn Inorganic compounds
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
76.80.+y Mössbauer effect; other γ-ray spectroscopy

Extension of Tsu-Esaki model for effective mass effects in resonant tunneling

J. N. Schulman

Appl. Phys. Lett. 72, 2829 (1998); http://dx.doi.org/10.1063/1.121471 (3 pages) | Cited 7 times

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The Tsu-Esaki model for resonant tunneling is extended to include the effects of differing in-plane masses in the emitter and well. The improvement produces features in the current versus voltage characteristic previously thought to require a much higher level of theoretical sophistication. The interband tunneling case can for the first time also be included in this simple and convenient framework. Calculations demonstrate that the first order contribution to the magnitude of the negative resistance is due to the mass difference, even when the same semiconductor is used in the emitter and well. A simple analytical SPICE-compatible I(V) formula is also derived. © 1998 American Institute of Physics.  
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85.30.De Semiconductor-device characterization, design, and modeling
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.50.Fq High-field and nonlinear effects
72.20.Ht High-field and nonlinear effects
73.40.Gk Tunneling
85.35.Ds Quantum interference devices
73.23.-b Electronic transport in mesoscopic systems

Improvement of Ta diffusion barrier performance in Cu metallization by insertion of a thin Zr layer into Ta film

Joon Seop Kwak, Hong Koo Baik, Jong-Hoon Kim, and Sung-Man Lee

Appl. Phys. Lett. 72, 2832 (1998); http://dx.doi.org/10.1063/1.121472 (3 pages) | Cited 3 times

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In order to increase the failure temperature of Ta diffusion barrier for Cu, we investigated the effect of insertion of a thin Zr layer into Ta film with/without ion bombardment on Ta diffusion barrier performance in Cu metallization. The insertion of a thin Zr layer into Ta film improved barrier properties significantly when the Ta/Zr/Ta barrier layers were deposited with concurrent ion bombardment. The significant improvement of Ta diffusion barrier properties by insertion of a thin Zr layer into Ta film with ion bombardment was attributed to the densification of grain boundaries in Ta/Zr/Ta films and the formation of an intermixing layer between Ta and Zr by ion bombardment, followed by the reduction of fast diffusion of Cu through Ta/Zr/Ta films. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Mm Grain and twin boundaries
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Stacked high-ϵ gate dielectric for gigascale integration of metal–oxide–semiconductor technologies

P. K. Roy and I. C. Kizilyalli

Appl. Phys. Lett. 72, 2835 (1998); http://dx.doi.org/10.1063/1.121473 (3 pages) | Cited 55 times

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Advances in lithography and thinner SiO2 gate oxides have enabled the scaling of metal–oxide–semiconductor technologies to sub-0.25 μm feature size. A major hurdle in the gate dielectric scaling using conventional thermally grown SiO2 has been excessive tunneling that occurs in ultrathin (<25 Å) SiO2. High dielectric constant materials such as Ta2O5 have been suggested as a substitute for SiO2. However, these materials have high concentrations of bulk fixed charge, unacceptable levels of Si–Ta2O5 interface trap states, and low silicon interface carrier mobilities. This letter summerizes an elegant solution to these issues through synthesis of a thermally grown SiO2(15 Å)–Ta2O5(30 Å)–SiO2(5–10 Å) dielectric with improvements in leakage, tunneling, charge trapping behavior, and interface substructure. Transistors fabricated using this stacked gate dielectric exhibit excellent subthreshold, saturation, and drive currents.
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85.40.Sz Deposition technology
85.30.Tv Field effect devices
77.22.Ch Permittivity (dielectric function)
68.35.Ct Interface structure and roughness
73.40.Gk Tunneling

Fine structure of near-band-edge photoluminescence in He+-irradiated GaN grown on SiC

V. A. Joshkin, C. A. Parker, S. M. Bedair, L. Y. Krasnobaev, J. J. Cuomo, R. F. Davis, and A. Suvkhanov

Appl. Phys. Lett. 72, 2838 (1998); http://dx.doi.org/10.1063/1.121474 (3 pages) | Cited 8 times

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The effect of He ion implantation on the optical properties of epitaxial GaN-on-SiC was studied. We observed that He+ irradiation increases the relative intensity of the “blue emission” and resistivity of GaN films and decreases the intensity of the near-band-edge photoluminescence. Because the intensity of the main peak is drastically decreased, the fine structure of the near-band-edge photoluminescence in GaN after He+ irradiation was observed. From a comparison of observed sharp lines with photoluminescence peaks of GaN doped with oxygen, we conclude that oxygen can produce a complex, which is characterized by a strong localization of free carriers and a large lattice distortion. The zero-phonon line of this defect has energy close to the band-gap energy of GaN. © 1998 American Institute of Physics.
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78.66.Li Other semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Ht Other nonmetals
63.20.-e Phonons in crystal lattices

Electrical characteristics of magnesium-doped gallium nitride junction diodes

J. B. Fedison, T. P. Chow, H. Lu, and I. B. Bhat

Appl. Phys. Lett. 72, 2841 (1998); http://dx.doi.org/10.1063/1.121475 (3 pages) | Cited 37 times

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Electrical characteristics of lateral p+n diodes made from gallium nitride epitaxial layers on sapphire substrates are reported. The current–voltage characteristics are observed to have several distinct regions in which a tunneling current has been identified at low forward bias in addition to the conventional temperature-dependent diffusion current observed at moderate forward bias. A tunneling behavior indicates the presence of deep-level traps at the junction, which alter the electrical behavior of these junctions compared to the conventional behavior. In addition, space-charge-limited currents are found to influence these junctions at large forward and reverse bias. © 1998 American Institute of Physics.
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85.30.Kk Junction diodes
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
73.50.Fq High-field and nonlinear effects
72.20.Ht High-field and nonlinear effects

Coherent control of acoustic phonons in semiconductor superlattices

Albrecht Bartels, Thomas Dekorsy, Heinrich Kurz, and Klaus Köhler

Appl. Phys. Lett. 72, 2844 (1998); http://dx.doi.org/10.1063/1.121476 (3 pages) | Cited 38 times

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Coherent acoustic phonons are generated in GaAs/AlAs superlattices by excitation with femtosecond laser pulses. Several modes of the acoustic phonon spectrum are observed, in agreement with the effect of zone folding in the mini-Brillouin zone of the superlattice. By applying successive pump pulses we are able to silence the first back-folded mode near q = 0, while selectively enhancing the coherent amplitude of higher order backfolded modes. This increase in the spectroscopic sensitivity opens the way to detailed time resolved studies of higher order acoustic modes in superlattices. © 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
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.35.Ja Surface and interface dynamics and vibrations
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Interface flattening and optical characteristics of GaAs/Al0.3Ga0.7As quantum wells grown on finite patterns on a GaAs(111)B substrate

Toshio Nishida and Naoki Kobayashi

Appl. Phys. Lett. 72, 2847 (1998); http://dx.doi.org/10.1063/1.121477 (3 pages)

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The formation of an atomically flat quantum well is studied by using metalorganic vapor phase epitaxy on a GaAs(111)B substrate. The surface of a 1-nm-thick GaAs layer on Al0.3Ga0.7As, corresponding to the upper interface of a quantum well, becomes stepfree on a 3.5-μm-wide mesa, and the surface of an Al0.3Ga0.7As barrier becomes stepfree on a 2.5-μm-wide mesa. On 15-μm-wide mesas, the stepfree area becomes 4–6 μm for the GaAs surface and 3–4.5 μm for Al0.3Ga0.7As, which are a few times wider than those obtained on planar substrates. The photoluminescence from different thickness quantum wells are spatially separated. © 1998 American Institute of Physics.
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81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Ct Interface structure and roughness
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors

Intermixing induced changes in the radiative emission from III–V quantum dots

C. Lobo, R. Leon, S. Fafard, and P. G. Piva

Appl. Phys. Lett. 72, 2850 (1998); http://dx.doi.org/10.1063/1.121478 (3 pages) | Cited 32 times

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We have examined the effect of thermally induced interdiffusion on the luminescence emission from red and infrared emitting self-assembled III–V quantum dots. Three different combinations of dot/barrier materials have been investigated: InAlAs/AlGaAs, InGaAs/AlGaAs and InGaAs/GaAs. In all cases, thermal intermixing was found to result in significant blueshifts of the photoluminescence (PL) emission. In addition, narrowing of the linewidth of the inhomogeneously broadened PL peak was observed. Both effects were found to be strongly dependent on the material system and average dot size. InAlAs/AlGaAs quantum dots exhibited the greatest linewidth reduction after intermixing, indicating this to be a promising method of achieving narrower luminescence lines for devices such as red-emitting zero-dimensional lasers. © 1998 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
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