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9 Aug 1999

Volume 75, Issue 6, pp. 745-878

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Photoconductive detection of millimeter waves using proton implanted GaAs

C. S. Wong, J. M. Dai, and H. K. Tsang

Appl. Phys. Lett. 75, 745 (1999); http://dx.doi.org/10.1063/1.124499 (3 pages) | Cited 1 time

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We show that ion-damaged GaAs may be used to detect millimeter electromagnetic waves in photoconductive sampling gates. The semi-insulating GaAs material which was implanted with a dose of 1014 cm−2 protons at an energy of 200 keV gave a signal to noise improvement of about 11.4 dB when compared with as-grown semi-insulating GaAs. The improvement is in spite of a reduced carrier mobility in the ion-implanted material and is due to the shorter carrier lifetime and formation of ohmic contacts with the ion-damaged semi-insulating GaAs. © 1999 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
61.72.uj III-V and II-VI semiconductors
61.82.Fk Semiconductors
84.40.Ba Antennas: theory, components and accessories
61.80.Jh Ion radiation effects
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.40.Ns Metal-nonmetal contacts

Temperature dependence of the stimulated emission in a conjugated polymer

Ch. Spiegelberg, N. Peyghambarian, and B. Kippelen

Appl. Phys. Lett. 75, 748 (1999); http://dx.doi.org/10.1063/1.124500 (3 pages) | Cited 12 times

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We report measurements of photoluminescence and stimulated emission of poly(2,5bis(2′-ethylhexyloxy)-1,4-phenylenevinylene for temperatures between 15 and 300 K. We show that the threshold for spectral line narrowing depends only slightly on the temperature. The observed decrease of the threshold intensity at lower temperatures can be mainly attributed to an increase of the quantum efficiency. We assign this deviation from the expected behavior for a four-level system to the dominant inhomogeneous broadening. © 1999 American Institute of Physics.
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78.45.+h Stimulated emission
78.66.Qn Polymers; organic compounds
42.70.Hj Laser materials
42.70.Jk Polymers and organics
78.55.Kz Solid organic materials

Influence of electric field on the behavior of Si nanoparticles generated by laser ablation

Junichi Muramoto, Ippei Sakamoto, Yoshiki Nakata, Tatsuo Okada, and Mitsuo Maeda

Appl. Phys. Lett. 75, 751 (1999); http://dx.doi.org/10.1063/1.124501 (3 pages) | Cited 9 times

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The influence of an electric field on particle behavior was investigated to control the transport of Si nanoparticles in a laser ablation plume by an ultraviolet Rayleigh scattering (UV-RS) technique. The majority of the nanoparticles, which could be observed by the UV-RS technique, were transported to the negatively biased electrode, indicating that they were positively charged. The deposition efficiency of nanoparticles onto a substrate was also improved by applying an electric field. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Fg Pulsed laser ablation deposition
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Vs Fine-particle systems
61.46.-w Structure of nanoscale materials
78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors

Diffraction from oxide confinement apertures in vertical-cavity lasers

P. A. Roos, J. L. Carlsten, D. C. Kilper, and K. L. Lear

Appl. Phys. Lett. 75, 754 (1999); http://dx.doi.org/10.1063/1.124502 (3 pages) | Cited 3 times

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Direct measurement of scattered fields from oxide confinement apertures in vertical-cavity lasers is presented. Diffraction fringes associated with each transverse lasing mode are detected in the far field from devices with varying oxide aperture dimensions and with quantum efficiencies as high as 48%. The diffracted pattern symmetries match the rectangular symmetry of the oxide apertures present in the devices and fringe locations are compared to Fraunhofer theory. The fraction of power diffracted from the lasing mode remains roughly constant as a function of relative pump rate, but is shown to depend on both transverse mode order and oxide aperture size. © 1999 American Institute of Physics.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.25.Fx Diffraction and scattering

Widely tunable continuous-wave THz laser

Yu. P. Gousev, I. V. Altukhov, K. A. Korolev, V. P. Sinis, M. S. Kagan, E. E. Haller, M. A. Odnoblyudov, I. N. Yassievich, and K.-A. Chao

Appl. Phys. Lett. 75, 757 (1999); http://dx.doi.org/10.1063/1.124503 (3 pages) | Cited 46 times

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We present experimental results on continuous-wave generation of THz radiation by strained Ge and a theoretical model for population inversion of carriers giving rise to the stimulated THz emission. Resonant acceptor states induced by strain and resonance hole scattering under applied electric field are necessary for the inversion. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Cy Elemental semiconductors
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
71.20.Mq Elemental semiconductors
71.55.Cn Elemental semiconductors
42.50.-p Quantum optics
62.20.F- Deformation and plasticity
72.20.Ht High-field and nonlinear effects
42.60.Fc Modulation, tuning, and mode locking

Improvement of amorphous-carbon active-layer thin-film light-emitting diodes using room-temperature ultrasound treatment

Woo Yeong Cho, Koeng Su Lim, and S. Ostapenko

Appl. Phys. Lett. 75, 760 (1999); http://dx.doi.org/10.1063/1.124504 (3 pages) | Cited 1 time

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Ultrasound treatment (UST) applied at room temperature enhances electroluminescent intensity (maximum at 600 nm) and optical output in thin-film light-emitting diodes with hydrogenated amorphous-carbon as an active layer. This positive UST effect is attributed to a reduction of the diode series resistance caused by a change of the interface and contact resistances. The UST effect is saturated with increase of the ultrasound amplitude. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Db Elemental semiconductors and insulators
78.66.Jg Amorphous semiconductors; glasses
43.35.Ty Other physical effects of sound
81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
73.40.Cg Contact resistance, contact potential
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
62.65.+k Acoustical properties of solids
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Optical resonance modes in GaN pyramid microcavities

H. X. Jiang, J. Y. Lin, K. C. Zeng, and W. Yang

Appl. Phys. Lett. 75, 763 (1999); http://dx.doi.org/10.1063/1.124505 (3 pages) | Cited 25 times

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An array of GaN hexagonal pyramids with a side length of 8.0 μm was fabricated by selective epitaxial overgrowth. These microsized pyramids are highly efficient microcavities. Three types of optical resonance modes with mode spacings of 10, 5.0, and 6.0 Å were observed when a single pyramid was pumped optically by an intense ultraviolet laser beam. An optical ray tracing method has been developed for calculating the optical resonance modes inside the pyramid microcavities. It was shown that a single pyramidal cavity can support several different types of optical resonance modes. The calculated mode spacing agrees very well with the observations. The uniqueness and advantages of this class of hexagonal pyramidal microcavities over the other microcavities are discussed. The implications of our finding on the future GaN microcavity light emitters including micro-light-emitting diodes, microcavity lasers, and vertical-cavity-surface emitting lasers are also discussed. © 1999 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.15.Dp Wave fronts and ray tracing
42.55.Px Semiconductor lasers; laser diodes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Significant improvement of device durability in organic light-emitting diodes by doping both hole transport and emitter layers with rubrene molecules

Gosuke Sakamoto, Chihaya Adachi, Toshiki Koyama, Yoshio Taniguchi, Charles D. Merritt, Hideyuki Murata, and Zakya H. Kafafi

Appl. Phys. Lett. 75, 766 (1999); http://dx.doi.org/10.1063/1.124506 (3 pages) | Cited 42 times

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We have developed highly durable organic light-emitting diodes. The basic structure of the diodes is anode/hole injection layer/hole transport layer+dopant/emitter layer+dopant/cathode. Both the hole transport and the emitter layers were doped with the highly fluorescent rubrene molecules. With the doping of both layers, 85% of the initial luminance was successively maintained even after 1000 h of continuous operation under constant current driving. Doping of only one of these layers, either the hole transport layer or emitter layer, on the other hand, resulted in shorter lifetime. We mention the possible mechanisms of the doping that enhance the device duration. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds

A photoconductive model for superior GaAs THz photomixers

E. R. Brown

Appl. Phys. Lett. 75, 769 (1999); http://dx.doi.org/10.1063/1.124507 (3 pages) | Cited 33 times

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Theoretical methods are used to evaluate the THz output from photomixer structures consisting of interdigitated electrodes and planar antennas on top of a low-temperature-grown GaAs layer. Consistent with experiment, the THz power from a standard photomixer is found to be limited by low external quantum efficiency (∼1%). This arises primarily from low photoconductive gain, which is attributed to a long transit time (between electrodes) for the majority of photocarriers generated in the structure. The modeling is then applied to an improved structure containing a thinner absorbing layer (≈0.34 μm for λ = 0.85 μmpump) with a dielectric mirror below it to induce resonant-cavity absorption near the surface where the gain is higher. Through increased gain and absorptivity, the model predicts ≈7× greater THz output for the same optical pump power. © 1999 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
85.30.De Semiconductor-device characterization, design, and modeling
85.60.Bt Optoelectronic device characterization, design, and modeling
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
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Variable profile capillary discharge for improved phase matching in a laser wakefield accelerator

D. Kaganovich, P. Sasorov, C. Cohen, and A. Zigler

Appl. Phys. Lett. 75, 772 (1999); http://dx.doi.org/10.1063/1.124508 (3 pages) | Cited 39 times

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We have demonstrated the possibility to generate long plasma channels with a variable plasma density profile in a longitudinal direction. Such plasma channels can be used to control the velocity of the guided high-intensity laser beams in order to extend the acceleration distance. The measured plasma density profiles at the capillary exit were found in excellent agreement with the numerical simulations. © 1999 American Institute of Physics.
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41.75.Jv Laser-driven acceleration
29.20.-c Accelerators
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Soft x-ray measurements of z-pinch-driven vacuum hohlraums

K. L. Baker, J. L. Porter, L. E. Ruggles, G. A. Chandler, Chris Deeney, M. Vargas, Ann Moats, Ken Struve, J. Torres, J. McGurn, W. W. Simpson, D. L. Fehl, R. E. Chrien, W. Matuska, and G. C. Idzorek

Appl. Phys. Lett. 75, 775 (1999); http://dx.doi.org/10.1063/1.124509 (3 pages) | Cited 18 times

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This letter reports the experimental characterization of a z-pinch-driven vacuum hohlraum. We have measured soft x-ray fluxes of 5×1012 W/cm2 radiating from the walls of hohlraums which are 2.4–2.5 cm in diameter by 1 cm tall. The x-ray source used to drive these hohlraums was a z pinch consisting of a 300 wire tungsten array driven by a 20 MA, 100 ns current pulse. In this hohlraum geometry, the z-pinch x-ray source can produce energies in excess of 800 kJ and powers in excess of 100 TW to drive these hohlraums. The x rays released in these hohlraums represent greater than a factor of 25 in energy and more than a factor of 3 in x-ray power over previous laboratory-driven hohlraums. © 1999 American Institute of Physics.
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52.55.Ez Theta pinch
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.57.-z Laser inertial confinement
28.52.Av Theory, design, and computerized simulation
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The photoluminescence from hydrogen-related species in composites of SiO2 nanoparticles

Yuri D. Glinka, Sheng-Hsien Lin, and Yit-Tsong Chen

Appl. Phys. Lett. 75, 778 (1999); http://dx.doi.org/10.1063/1.124510 (3 pages) | Cited 55 times

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Measurements of photoluminescence (PL) from composites of silica nanoparticles (the primary particle size 7 and 15 nm) as a function of heat treatment temperature show that the PL results from hydrogen-related species and thermally produced structural defects. The PL was induced by an ArF or Nd:YAG (yttrium–aluminum–garnet) laser (λexc = 193 or 266 nm). The green PL exhibits a progression with spacings of about Δν = 630 cm−1 assigned to the bending vibration of ≡Si–H on the surface of particles. The spacings increase up to Δν = 1200 cm−1 when ≡Si–H and nonbridging oxygen (≡Si–O•) form interfacial water species. © 1999 American Institute of Physics.
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78.66.Nk Insulators
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
63.20.-e Phonons in crystal lattices
81.40.Tv Optical and dielectric properties related to treatment conditions

An isolated silicon single chain end-grafted onto a substrate surface

K. Furukawa, K. Ebata, and N. Matsumoto

Appl. Phys. Lett. 75, 781 (1999); http://dx.doi.org/10.1063/1.124511 (3 pages) | Cited 11 times

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We report atomic force microscopy images of one-dimensional silicon chains (polysilanes) individually bonded to a substrate surface [quartz glass (SiO2), sapphire (Al2O3), and Si(111)]. The sample was prepared by a one-to-one chemical reaction between a reactive anchor of alkylbromide on the surface and a polysilanyl lithium. We observed dot images with variable densities which depended on the reactive anchor density. Each dot, with a diameter of about 20 nm and a height of about 5 nm, corresponded to an isolated single polysilane molecule with a collapsed structure typical of usual end-grafted polymers under poor solvent conditions. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

The mechanism of micropipe nucleation at inclusions in silicon carbide

M. Dudley, X. R. Huang, W. Huang, A. Powell, S. Wang, P. Neudeck, and M. Skowronski

Appl. Phys. Lett. 75, 784 (1999); http://dx.doi.org/10.1063/1.124512 (3 pages) | Cited 42 times

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A model is presented for a possible mechanism of screw dislocation (including micropipe) nucleation in silicon carbide. The model is based on the observation of micropipe nucleation at the sites of foreign material inclusions using synchrotron white beam x-ray topography and transmission optical microscopy. It is shown that incorporation of the inclusion into the growing crystal can lead to deformation of the protruding ledge which constitutes the overgrowing layer. Accommodation of this deformation into the crystal lattice leads to the production of pairs of opposite sign screw dislocations which then propagate with the growing crystal. Evidence for the existence of such pairs of dislocations is presented. © 1999 American Institute of Physics.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Bb Theories and models of crystal defects
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Characterization of the silicon on insulator film in bonded wafers by high resolution x-ray diffraction

G. M. Cohen, P. M. Mooney, E. C. Jones, K. K. Chan, P. M. Solomon, and H-S. P. Wong

Appl. Phys. Lett. 75, 787 (1999); http://dx.doi.org/10.1063/1.124513 (3 pages) | Cited 16 times

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High resolution x-ray diffraction (HRXRD) is proposed as a nondestructive tool for the characterization of the silicon on insulator (SOI) film in bonded wafers. Although the bonded stack may consist of many amorphous layers, the measured diffraction spectra only show the crystalline SOI layer, thus providing a direct measurement of the film. We have demonstrated that HRXRD is capable of accurately measuring the film thickness, the tilt of the film planes with respect to the substrate planes, and the rotation misalignment of the bonded film with respect to the carrier substrate. SOI films with thicknesses down to 30 nm were readily measured with accuracy better than 1%. It is shown that an angular separation between the layer and the substrate diffraction peaks is maintained due to an unintentional miscut which usually exists in the starting wafers used for bonding. This angular separation is unique to bonded wafers as opposed to separation by implanted oxygen (SIMOX) wafers where the layer and substrate peaks are nonseparable. Calculated diffraction spectra based on the kinematic approach showed excellent agreement with the measured diffraction. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
61.05.cp X-ray diffraction

Optical transitions in Pr-implanted GaN

J. M. Zavada, R. A. Mair, C. J. Ellis, J. Y. Lin, H. X. Jiang, R. G. Wilson, P. A. Grudowski, and R. D. Dupuis

Appl. Phys. Lett. 75, 790 (1999); http://dx.doi.org/10.1063/1.124514 (3 pages) | Cited 15 times

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Photoluminescence (PL) spectroscopy has been used to investigate praseodymium (Pr) related transitions in Pr-implanted GaN. Wurtzite GaN epilayers were grown by metalorganic chemical vapor deposition on sapphire substrates and subsequently ion implanted with Pr to a dose of 5.7×1013/cm2. The implanted samples were annealed in nitrogen to facilitate recovery from implantation related damage. Narrow PL emission bands related to 4f intrashell transitions of the trivalent Pr ion were observed near 650, 950, 1100, and 1300 nm. The dependence of PL emission on sample temperature, excitation intensity, oxygen incorporation, and annealing temperature was systematically studied. We find that the PL efficiency increases exponentially with annealing temperature up to the maximum temperature of 1050 °C applied in the current study. Furthermore, the PL emission shows no evidence of significant thermal quenching over the sample temperature range of 10–300 K. This thermal stability will have particular advantages for applications in high temperature optoelectronic devices. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
71.55.Eq III-V semiconductors

Sensitization of Er3+ emission at 1.5 μm in SiO2 thermally grown on silicon by coimplantation of Yb

A. Kozanecki, K. Homewood, and B. J. Sealy

Appl. Phys. Lett. 75, 793 (1999); http://dx.doi.org/10.1063/1.124515 (3 pages) | Cited 9 times

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Effects of Yb codoping on the photoluminescence of Er3+ ions at room temperature in SiO2 films thermally grown on silicon are investigated. We demonstrate that for an excitation wavelength of 488 nm Yb ions act as efficient sensitizers of the 4I13/2–4I15/2 emission of Er3+ ions. We have found that for the fixed dose of Yb the Er3+ intensity is directly proportional to the Er concentration. Enhancement by a factor of 15 due to Yb codoping has been observed. A model of the mechanism responsible for sensitization is discussed. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
61.72.up Other materials

Phosphorus and arsenic profile control for high performance epitaxial base bipolar junction devices

R. Bashir, A. E. Kabir, and P. Westrom

Appl. Phys. Lett. 75, 796 (1999); http://dx.doi.org/10.1063/1.124516 (3 pages) | Cited 3 times

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In this study, we report on the incorporation behavior of n-type species in undoped layers grown subsequent to doped layers at low temperature (700–750 °C) reduced pressure chemical vapor deposition of silicon/silicon germanium (Si/Si1−xGex) performed in a single wafer epitaxial deposition system. Significant amounts of these species are observed even in an undoped layer grown subsequent to the doped layer. The presence of these dopants in the subsequently grown undoped layer is attributed to segregation at the moving growth interface. The arsenic segregation is confirmed to be significantly higher than phosphorus. In addition, an increase in both the phosphorus and arsenic incorporation is observed in the presence of a highly doped boron layer. © 1999 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.up Other materials
61.72.uf Ge and Si
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
85.30.Pq Bipolar transistors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Magnetophotoluminescence of stacked self-assembled InP quantum dots

R. Provoost, M. Hayne, V. V. Moshchalkov, M. K. Zundel, and K. Eberl

Appl. Phys. Lett. 75, 799 (1999); http://dx.doi.org/10.1063/1.124517 (3 pages) | Cited 15 times

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We report magnetophotoluminescence measurements of stacked layers of self-assembled InP quantum dots. With a magnetic field applied in the growth direction we have determined the exciton reduced mass from the field dependence of the photoluminescence energy. By applying a magnetic field perpendicular to the growth direction, we have analyzed the spatial confinement of the dots in the growth direction. We observe a large increase in the shift of the exciton energy between 0 and 50 T when the thickness of the GaInP spacer layer between the dots is reduced from 8 to 4 nm. This indicates a decrease in spatial confinement in the growth direction which we attribute to strong electronic coupling between vertically stacked dots. © 1999 American Institute of Physics.  
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Ls Magneto-optical effects
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Ji Excitons in magnetic fields; magnetoexcitons

Mn-doped ZnS nanoparticles as efficient low-voltage cathodoluminescent phosphors

A. D. Dinsmore, D. S. Hsu, H. F. Gray, S. B. Qadri, Y. Tian, and B. R. Ratna

Appl. Phys. Lett. 75, 802 (1999); http://dx.doi.org/10.1063/1.124518 (3 pages) | Cited 38 times

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We have synthesized nanoparticles of ZnS doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays (FEDs). We show that the cathodoluminescent efficiency of particles ⩽100 nm in diameter is within 40% of that of a commercial (micron-sized) phosphor when the electron-beam energy ranges between 500 and 3500 eV. The nanoparticles exhibit less current saturation than larger-sized phosphors, an important feature for use in FEDs. Furthermore, the nanoparticles were annealed at just 535 °C, hundreds of degrees below the processing temperatures of standard phosphors. Finally, we discuss the effect of the particle surface on low-voltage luminous efficiency. © 1999 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
85.45.Fd Field emission displays (FEDs)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Dz II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Freely migrating defects in ion-irradiated Cu3Au

L. C. Wei, E. Lang, C. P. Flynn, and R. S. Averback

Appl. Phys. Lett. 75, 805 (1999); http://dx.doi.org/10.1063/1.124519 (3 pages) | Cited 9 times

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The efficiency of producing freely migrating vacancy defects in irradiated Cu3Au was examined using electrical resistivity measurements of radiation-induced ordering on highly perfect single-crystal films. Relative efficiencies for He, Ne, and Ar bombardments at different ion energy and specimen temperature were obtained. The ratio of the efficiencies of 0.6 MeV Ne to He increased with temperature from ∼ 0.25 at 340 K to a saturation value of ∼ 0.40 at 520 K. For Ar and He, the ratio increased from ∼ 0.11 at 360 K to ∼ 0.18 at 540 K. Estimates indicate that about half of all defects created in cascades are freely migrating. © 1999 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
61.72.J- Point defects and defect clusters
66.30.Lw Diffusion of other defects
73.61.At Metal and metallic alloys
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Inversion of wurtzite GaN(0001) by exposure to magnesium

V. Ramachandran, R. M. Feenstra, W. L. Sarney, L. Salamanca-Riba, J. E. Northrup, L. T. Romano, and D. W. Greve

Appl. Phys. Lett. 75, 808 (1999); http://dx.doi.org/10.1063/1.124520 (3 pages) | Cited 82 times

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Magnesium incorporation during the molecular-beam epitaxy growth of wurtzite GaN is found to invert the Ga-polar (0001) face to the N-polar face. The polarity is identified based on the two different sets of reconstructions seen on the film prior to and after about 1 monolayer Mg exposure. The inversion boundary is seen to lie on the (0001) plane from transmission electron microscopy images, and a structural model is presented for the inversion. On the Ga-polar face, Mg is also seen to stabilize growth in the N-rich regime. © 1999 American Institute of Physics.
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68.35.Rh Phase transitions and critical phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Ea III-V semiconductors

Production and annealing of electron irradiation damage in ZnO

D. C. Look, D. C. Reynolds, J. W. Hemsky, R. L. Jones, and J. R. Sizelove

Appl. Phys. Lett. 75, 811 (1999); http://dx.doi.org/10.1063/1.124521 (3 pages) | Cited 149 times

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High-energy (>1.6 MeV) electrons create acceptors and donors in single-crystal ZnO. Greater damage is observed for irradiation in the [0001] direction (Zn face) than in the [000math] direction (O face). The major annealing stage occurs at about 300–325 °C, and is much sharper for defects produced by Zn-face irradiation, than for those resulting from O-face irradiation. The defects appear to have a chain character, rather than being simple, near-neighbor vacancy/interstitial Frenkel pairs. These experiments suggest that ZnO is significantly more “radiation hard” than Si, GaAs, or GaN, and should be useful for applications in high-irradiation environments, such as electronics in space satellites. © 1999 American Institute of Physics.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
61.72.Cc Kinetics of defect formation and annealing
71.55.Gs II-VI semiconductors
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High-temperature light emission from InAs quantum dots

A. Patanè, A. Polimeni, P. C. Main, M. Henini, and L. Eaves

Appl. Phys. Lett. 75, 814 (1999); http://dx.doi.org/10.1063/1.124522 (3 pages) | Cited 23 times

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We study the photoluminescence (PL) properties of InAs/GaAs self-assembled quantum dots in a temperature range (T = 300–500 K) above that reported to date. Various power excitation densities were used, allowing us to identify the important contribution of nonradiative channels in quenching the dot PL as the temperature is increased. The role played by the wetting layer on the dot PL intensity has been investigated in samples in which the separation of the dot and wetting layer levels is tuned by post-growth annealing. This experiment reveals that, at a high temperature (>300 K), the relative population of the dot and wetting layer levels is given by a Boltzmann distribution. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.40.Gh Other heat and thermomechanical treatments

Modeling of Ge surface segregation in vapor-phase deposited Si1−xGex thin films

Y.-J. Zheng, A. M. Lam, and J. R. Engstrom

Appl. Phys. Lett. 75, 817 (1999); http://dx.doi.org/10.1063/1.124523 (3 pages) | Cited 12 times

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Recent experimental results concerning Ge segregation in Si1−xGex epitaxial thin films deposited on Si(100) substrates using Si2H6 and GeH4 cannot be accounted for by a simple two-site model involving surface and bulk states. This is due to Ge enrichment in the subsurface layers. Here, we demonstrate that a simple model based on the regular solution theory, which invokes both nearest, and next-nearest neighbor interactions, can explain the Ge enrichment in the subsurface. A computer simulation using the Monte Carlo method verifies the assumptions made in the model, and both methods show excellent agreement with the experimental data. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation
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