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16 Sep 1996

Volume 69, Issue 12, pp. 1657-1813

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A novel sensitized photochromic organic glass for holographic optical storage

R. Wortmann, P. M. Lundquist, R. J. Twieg, C. Geletneky, C. R. Moylan, Y. Jia, R. G. DeVoe, D. M. Burland, M.‐P. Bernal, H. Coufal, R. K. Grygier, J. A. Hoffnagle, C. M. Jefferson, R. M. Macfarlane, R. M. Shelby, et al.

Appl. Phys. Lett. 69, 1657 (1996); http://dx.doi.org/10.1063/1.117018 (3 pages) | Cited 11 times

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A new class of photochromic glasses for use in irreversible holographic optical storage applications is described. The recording mechanism involves a triplet‐sensitized photoreaction of an organic chromophore. The materials are isotropic and red‐sensitive, and exhibit high diffraction efficiencies and long hologram lifetimes. The wavelength sensitivity can be adjusted by the choice of sensitizer; C60, sensitive in the red, is described here. Single digital data page recording and error‐free readout are demonstrated at a density of 0.5 Mb/cm2; multiplexing in a 150‐μm‐thick sample is also demonstrated. © 1996 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.70.Gi Light-sensitive materials
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics

Efficient continuous wave blue light generation in optical superlattice LiNbO3 by direct frequency doubling a 978 nm InGaAs diode laser

Ya‐lin Lu, Yan‐qing Lu, Jian‐jun Zheng, Cheng‐cheng Xue, Xiang‐fei Cheng, Gui‐peng Luo, and Nai‐ben Ming

Appl. Phys. Lett. 69, 1660 (1996); http://dx.doi.org/10.1063/1.117019 (2 pages) | Cited 2 times

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First‐order quasiphase matched blue light generation in a LiNbO3 optical superlattice was performed by direct frequency doubling of a continuous wave 978‐nm diode laser. 1.27 mW output power of blue light was obtained with an incidence power of 500 mW. The frequency conversion efficiency is 0.25%. © 1996 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Simultaneous blue and green upconversion lasing in a laser‐diode‐pumped Pr3+/Yb3+ doped fluoride fiber laser

D. M. Baney, G. Rankin, and Kok Wai Chang

Appl. Phys. Lett. 69, 1662 (1996); http://dx.doi.org/10.1063/1.117020 (3 pages) | Cited 30 times

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An upconversion laser operating simultaneously at visible wavelengths of 520 and 490 nm under infrared semiconductor pumping is demonstrated. The Pr3+/Yb3+doped ZBLAN fluorozirconate fiber laser yielded 1.4 mW total power at green and blue wavelengths with approximately 350 mW of incident pump light at a wavelength of 856 nm. Threshold launched powers of 55 and 85 mW were obtained for the wavelengths of 520 and 490 nm, respectively. © 1996 American Institute of Physics.
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42.55.Xi Diode-pumped lasers
42.81.Wg Other fiber-optical devices

Light scattering in high‐dislocation‐density GaN

Z. L. Liau, R. L. Aggarwal, P. A. Maki, R. J. Molnar, J. N. Walpole, R. C. Williamson, and I. Melngailis

Appl. Phys. Lett. 69, 1665 (1996); http://dx.doi.org/10.1063/1.117021 (3 pages) | Cited 10 times

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Light scattering by edge dislocations and the resulting loss coefficient have been modeled for GaN layers. Phase‐front deformation caused by the refractive‐index variation in the dislocation’s strain field has been considered and the resulting scattering loss calculated. We show that the high dislocation densities observed in recent GaN layers can result in significant large loss coefficients. The present work also offers some insights for improved lasers. © 1996 American Institute of Physics.
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42.70.Hj Laser materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors

High‐volume production of laser‐polarized 129Xe

B. Driehuys, G. D. Cates, E. Miron, K. Sauer, D. K. Walter, and W. Happer

Appl. Phys. Lett. 69, 1668 (1996); http://dx.doi.org/10.1063/1.117022 (3 pages) | Cited 132 times

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A method is described for producing several liters of nuclear spin polarized 129Xe gas via spin exchange with an optically pumped Rb vapor. We use a 140 W AlGaAs laser diode array whose broad spectral output is efficiently absorbed by employing ∼10 atm of 4He to pressure broaden the Rb D1 absorption profile. 129Xe is polarized in a continuous gas flow and is then cryogenically accumulated and stored. Extensions of this technique should enable the production of tens of liters of 129Xe with a nuclear spin polarization of order 50%. Production of laser‐polarized 129Xe in liter quantities is important for the continued development of magnetic resonance imaging using spin‐polarized 129Xe. © 1996 American Institute of Physics.
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51.70.+f Optical and dielectric properties
87.61.-c Magnetic resonance imaging
42.62.-b Laser applications

Nonlinear distortion of a three‐tone modulated laser diode followed by an interferometer

G. Yabre

Appl. Phys. Lett. 69, 1671 (1996); http://dx.doi.org/10.1063/1.117023 (3 pages) | Cited 1 time

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The behavior of the light signal converted by means of a Mach‐Zehnder interferometer is analyzed under the assumption of a three‐tone modulation of the emitting laser source. The signal at the interferometer output is theoretically illustrated through the second‐order harmonic as well as the second‐ and third‐order intermodulation distortions. The corresponding direct intensity modulation (IM) distortions are also reported to facilitate a direct comparison with frequency modulation (FM). The results show that, as in the IM case, the FM‐to‐IM second‐ and third‐order intermodulation products (IMPs) generated by a three‐tone modulation result in a 6 dBc higher distortion level than the second‐order harmonic and the two‐tone third‐order IMPs, respectively. The results show, moreover, that the FM‐to‐IM interferometric conversion technique would lead to lower distortion levels over the classical direct IM, thereby imposing less rigid requirements on the laser linearity. © 1996 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
07.60.Ly Interferometers

Reconstruction of diffuse photon‐density wave interference in turbid media from time‐resolved transmittance measurements

Charlotta Lindquist, Antonio Pifferi, Roger Berg, Stefan Andersson‐Engels, and Sune Svanberg

Appl. Phys. Lett. 69, 1674 (1996); http://dx.doi.org/10.1063/1.117024 (3 pages) | Cited 3 times

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We demonstrate an improved technique to precisely localize inhomogeneities in turbid media by means of reconstructing diffuse photon‐density wave interference from time‐resolved transmittance measurements applying the Fourier transform. This interference can also be obtained in the reverse mode, that is using a single source and combining the signals detected at several locations. This increases the collection efficiency and the possibility for postprocessing and allows one to evaluate the data from one measurement in different ways to make the analysis more robust. © 1996 American Institute of Physics.
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87.64.K- Spectroscopy
87.80.-y Biophysical techniques (research methods)
42.25.Hz Interference
87.50.W- Optical/infrared radiation effects

Dynamics of photoexcited states and charge carriers in organic thin films: Alq3

Ardie D. Walser, Igor Sokolik, Richard Priestley, and Roger Dorsinville

Appl. Phys. Lett. 69, 1677 (1996); http://dx.doi.org/10.1063/1.117025 (3 pages) | Cited 11 times

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We demonstrate a method for observing and analyzing the dynamics of photoexcited molecular states and charge carriers in organic thin films, by measuring simultaneously the transient photoluminescence and photoconductivity. We show experimentally in tris‐(8‐hydroxyquinoline) aluminum (Alq3) that exciton–exciton annihilation dictates the behavior of the photoluminescence and photoconductivity at high excitation intensities. The experimental results are corroborated by calculations based on an exciton‐exciton annihilation model. © 1996 American Institute of Physics.
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42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
73.61.Ph Polymers; organic compounds

Low‐temperature study of current and electroluminescence in InGaN/AlGaN/GaN double‐heterostructure blue light‐emitting diodes

Piotr Perlin, Marek Osiński, Petr G. Eliseev, Vladimir A. Smagley, Jian Mu, Michael Banas, and Philippe Sartori

Appl. Phys. Lett. 69, 1680 (1996); http://dx.doi.org/10.1063/1.117026 (3 pages) | Cited 64 times

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Electrical and optical properties of Nichia double‐heterostructure blue light‐emitting diodes, with In0.06Ga0.94N:Zn, Si active layer, are investigated over a wide temperature range from 10 to 300 K. Current–voltage characteristics have complex character and suggest the involvement of various tunneling mechanisms. At small voltages (and currents), the peak wavelength of the optical emission shifts with the applied bias across a large spectral range from 539 nm (2.3 eV) up to 443 nm (2.8 eV). Light emission takes place even at the lowest temperatures, indicating that a complete carrier freeze‐out does not occur. © 1996 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.De Semiconductor-device characterization, design, and modeling
78.60.Fi Electroluminescence

Ultraviolet prepulse for enhanced x‐ray emission and brightness from droplet‐target laser plasmas

M. Berglund, L. Rymell, and H. M. Hertz

Appl. Phys. Lett. 69, 1683 (1996); http://dx.doi.org/10.1063/1.117027 (3 pages) | Cited 28 times

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We show that an ultraviolet prepulse significantly enhances the water‐window x‐ray emission and brightness for a droplet‐target laser plasma. By combining a 65 mJ, 120 ps, λ=532 nm main pulse with an up to 3 mJ prepulse, the emitted x‐ray photon flux may be increased more than eight times. The resulting C VI λ=3.37 nm line emission is more than 3×1012 photons/sr⋅pulse, corresponding to a conversion efficiency above 3%/line. The integrated spectral brightness is increased two times and is found to reach its maximum for different prepulse parameters than those resulting in maximum photon flux. © 1996 American Institute of Physics.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Thin film light emitting devices from an electroluminescent ruthenium complex

J.‐K. Lee, D. S. Yoo, E. S. Handy, and M. F. Rubner

Appl. Phys. Lett. 69, 1686 (1996); http://dx.doi.org/10.1063/1.117028 (3 pages) | Cited 71 times

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A ruthenium polypyridyl complex has been synthesized and examined as an emitter material in thin film electroluminescent devices. This material exhibits photoluminescent and electroluminescent effects as well as several reversible one‐electron oxidation and reduction processes. Electroluminescent devices fabricated from this ruthenium complex either via spin coating methods or self‐assembly techniques exhibit relatively high electroluminescent efficiencies and luminance levels in some cases as high as 100 cd/m2. © 1996 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds

A comparative study of ultraviolet emission with peak wavelengths around 350 nm from oxidized porous silicon and that from SiO2 powder

G. G. Qin, J. Lin, J. Q. Duan, and G. Q. Yao

Appl. Phys. Lett. 69, 1689 (1996); http://dx.doi.org/10.1063/1.117029 (3 pages) | Cited 60 times

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Ultraviolet (UV) light emission with almost the same peak wavelengths from thermally oxidized porous silicon (OPS) (340, 355, and 370 nm) and SiO2 powder (340, 350, and 370 nm) has been observed. Photoluminescence excitation spectra of OPS without Si nanoscale particles (SNP) and those of SiO2 powder are very similar, however, very different from those of the OPS with SNP. Three types of luminescence centers with luminescence wavelengths around 350 nm are responsible for UV light emission, and photoexcitation in OPS with SNP occurs in SNP as well as in Si oxide layers covering SNP. © 1996 American Institute of Physics.
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78.55.Mb Porous materials

Picosecond acoustic measurements of longitudinal wave velocity of submicron polymer films

Yung‐Chun Lee, Kathleen C. Bretz, Frank W. Wise, and Wolfgang Sachse

Appl. Phys. Lett. 69, 1692 (1996); http://dx.doi.org/10.1063/1.117030 (3 pages) | Cited 17 times

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We apply picosecond acoustic techniques to determine the longitudinal wave speed of submicron polymer films in the through‐thickness dimension. The time‐of‐flight of an elastic wave propagating through the polymer film is measured using an optical pump/probe technique. The longitudinal wave speed in poly(methyl methacrylate) films of thickness ranging from 20 to 130 nm has been determined. A pronounced increase in longitudinal wave speed is observed for films of thickness less than 40 nm. © 1996 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.30.+d Mechanical and elastic waves; vibrations

Characteristics of the high density plasma production by m=0 helicon wave

Y. Sakawa, N. Koshikawa, and T. Shoji

Appl. Phys. Lett. 69, 1695 (1996); http://dx.doi.org/10.1063/1.118001 (3 pages) | Cited 21 times

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The characteristics of the high density plasma production by the m = 0 azimuthal mode helicon wave is investigated. By varying the power of the applied radio frequency Prf two discharge modes exist; one is the low density mode (plasma density np<1012 cm−3), at which the discharge is sustained not by a helicon wave but by the antenna induction field at low Prf; the other is the high density mode (np≳1013 cm−3), in which helicon wave is excited at high Prf; in between the two modes, np jumps more than an order of magnitude. The threshold Prf for the density jump is higher for the m = 0 mode than that of the m = +1 and −1 modes excited by the helical antenna. © 1996 American Institute of Physics.
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52.50.Dg Plasma sources
52.35.-g Waves, oscillations, and instabilities in plasmas and intense beams
52.80.Pi High-frequency and RF discharges

X‐ray photoelectron spectroscopy of carbon nitride films deposited by graphite laser ablation in a nitrogen postdischarge

Malek Tabbal, Philippe Mérel, Simona Moisa, Mohamed Chaker, André Ricard, and Michel Moisan

Appl. Phys. Lett. 69, 1698 (1996); http://dx.doi.org/10.1063/1.118000 (3 pages) | Cited 69 times

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Carbon nitride thin films have been deposited on silicon substrates, using a newly developed surface wave discharge/pulsed laser deposition system. Nitrogen incorporation in the films is examined by x‐ray photoelectron spectroscopy (XPS). It shows that interaction between the laser ablated carbon species and nitrogen atoms from the surface‐wave N2 plasma enhances the incorporation of N in the carbon nitride layers, for example, up to 19% at a deposition pressure of 2 mTorr. Increasing the deposition temperature decreases nitrogen incorporation and changes the local chemical environment of nitrogen atoms. © 1996 American Institute of Physics.
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79.60.Dp Adsorbed layers and thin films
81.15.Fg Pulsed laser ablation deposition
81.05.Zx New materials: theory, design, and fabrication

Molecular dynamics calculation of the Zr(Ni) enthalpy of mixing

Fabrizio Cleri, Giorgio Mazzone, and Vittorio Rosato

Appl. Phys. Lett. 69, 1701 (1996); http://dx.doi.org/10.1063/1.118002 (3 pages) | Cited 5 times

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The Zr‐terminal portion of the Ni–Zr phase diagram was studied by means of molecular dynamics simulations. The internal energy and the enthalpy of mixing at 300 K of the α‐ and β‐Zr(Ni) solid solutions and of the Zr–Ni amorphous phase were calculated for Ni concentrations ≤10 at. %. The values of the enthalpy of mixing obtained are positive for the terminal solid solutions, and negative for the amorphous phase. This behavior is attributed to the differences in strain energy generated in the Zr lattice or in the amorphous phase by Ni atoms. Implications of these results relevant to the problem of amorphization in metallic systems by solid‐state reactions are discussed. © 1996 American Institute of Physics.
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61.43.Bn Structural modeling: serial-addition models, computer simulation
81.30.Bx Phase diagrams of metals, alloys, and oxides
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Electronic structure of the ferroelectric layered perovskite SrBi2Ta2O9

J. Robertson, C. W. Chen, W. L. Warren, and C. D. Gutleben

Appl. Phys. Lett. 69, 1704 (1996); http://dx.doi.org/10.1063/1.118003 (3 pages) | Cited 90 times

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The band structure of the layered perovskite SrBi2Ta2O9 (SBT) was calculated by tight binding and the valence band density of states was measured by x‐ray photoemission spectroscopy. We find both the valence and conduction band edges to consist of states primarily derived from the Bi–O layer rather than the perovskite Sr–Ta–O blocks. The valence band maximum arises from O p and some Bi s states, while the conduction band minimum consists of Bi p states, with a wide band gap of 5.1 eV. It is argued that the Bi–O layers largely control the electronic response whereas the ferroelectric response originates mainly from the perovskite Sr–Ta–O block. Bi and Ta centered traps are calculated to be shallow, which may account in part for its excellent fatigue properties. © 1996 American Institute of Physics.
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71.20.Ps Other inorganic compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Effect of phase coexistence at morphotropic phase boundary on the properties of Pb(ZrxTi1−x)O3 ceramics

S. K. Mishra, Dhananjai Pandey, and Anirudh P. Singh

Appl. Phys. Lett. 69, 1707 (1996); http://dx.doi.org/10.1063/1.118004 (3 pages) | Cited 39 times

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The temperature variation of planar electromechanical coupling coefficient (kp) in Pb(ZrxTi1−x)O3(PZT) ceramics near the morphotropic phase boundary (MPB) compositions has been correlated with structural changes to show that the maximum electromechanical response at a given composition (x) is a function of temperature (T) and occurs in the tetragonal phase field just outside the two‐phase MPB region in the (x,T) plane. This clearly disproves the hypothesis that the coexistence of rhombohedral and tetragonal phases at MPB is responsible for the enhancement of the electromechanical response. In fact, coexistence of the rhombohedral phase with the tetragonal phase is shown to lead to the lowering of the electromechanical response. © 1996 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point

Dipole tip model investigation of resonance effects in scanning tunneling microscopy

T. M. Kalotas, A. R. Lee, J. Liesegang, and A. Alexopoulos

Appl. Phys. Lett. 69, 1710 (1996); http://dx.doi.org/10.1063/1.118005 (3 pages) | Cited 2 times

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The distribution of the tunneling current in the semiclassical mode of operation of the scanning tunneling microscope is studied using an axially symmetric 3‐D tip. The tip is taken as an equipotential of a dipole, thus giving an analytical form for the potential and the field lines between the tip and the surface, with the latter taken to be atomically flat and corresponding to the zero equipotential plane. Field emission resonance calculations are made, allowing conductance and tip‐to‐surface separation to be determined as functions of bias voltage at constant current. Results are compared with the measurements of Becker, Golovchenko, and Swartzentruber [Phys. Rev. Lett. 55, 987 (1985)]. © 1996 American Institute of Physics.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Time‐dependent and trap‐related current conduction mechanism in ferroelectric Pb(ZrxTi1−x)O3 films

Hong‐Ming Chen, Jian‐Ming Lan, Jia‐Lin Chen, and Joseph Ya‐min Lee

Appl. Phys. Lett. 69, 1713 (1996); http://dx.doi.org/10.1063/1.118006 (3 pages) | Cited 14 times

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The correlation between trap density and leakage current of Pb(Zr53Ti47)O3 (PZT) capacitors is studied by examining the current–time (I–t) and the current–voltage (I–V) characteristics. The increase of leakage current after dc electrical field stress is correlated with the number of charges trapped inside the films. The spatial density distribution of trapped charges is calculated by analyzing the decay of discharging current after the application of dc stress. The discharging current is well fitted by a 1/t relationship where t is discharging time. This behavior can be explained by using the tunneling front model. A discharging process is proposed based on this consideration. © 1996 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.40.Rw Metal-insulator-metal structures
73.61.Ng Insulators
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Nucleation and bulk film growth kinetics of nanocrystalline diamond prepared by microwave plasma‐enhanced chemical vapor deposition on silicon substrates

Joungchel Lee, Byungyou Hong, R. Messier, and R. W. Collins

Appl. Phys. Lett. 69, 1716 (1996); http://dx.doi.org/10.1063/1.118007 (3 pages) | Cited 30 times

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Real time spectroscopic ellipsometry has been applied to characterize the substrate temperature (T) dependence of the deposition rates for nanocrystalline diamond thin films prepared by microwave plasma‐enhanced chemical vapor deposition on seeded Si substrates. With the real time capability, it is possible to determine the rates at which the diamond mass thickness (i.e., volume per area) increases during the early nucleation and bulk film growth regimes. The increases in the nucleating and bulk diamond growth rates with T for 400<T<800 °C are consistent with activation energies of ∼17 and 8 kcal/mol, respectively. The results reported here provide insights into the nature of the low‐T growth rate limitations for diamond films on nondiamond substrates. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
07.60.Fs Polarimeters and ellipsometers
78.66.Jg Amorphous semiconductors; glasses

Oriented growth of SrBi2Ta2O9 ferroelectric thin films

Seshu B. Desu, Dilip P. Vijay, X. Zhang, and BaoPing He

Appl. Phys. Lett. 69, 1719 (1996); http://dx.doi.org/10.1063/1.118008 (3 pages) | Cited 79 times

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We report on the ferroelectric properties of c‐axis oriented ferroelectric SrBi2Ta2O9 thin films. Pt/SrBi2Ta2O 9/Pt capacitors were grown on single crystal MgO (and/or SrTiO3) substrates using pulsed laser ablation. These substrates provide the necessary template for (100) texture in platinum due to their close lattice matching. This in turn facilitates the c‐axis orientation in the ferroelectric films. The degree of orientation in the layered structure ferroelectric film was systematically varied from highly c‐axis oriented to random polycrystalline by varying the growth conditions of the bottom metal electrode. The polarization and coercive field values were found to decrease with an increasing degree of c‐axis orientation; while the randomly oriented films exhibited a remnant polarization of 5 μC/cm 2, a coercive field of 70 kV/cm, and a dielectric constant of 320, the c‐axis oriented films exhibited very low polarization (∼1 μC/cm2), coercivity (22 kV/cm), and dielectric constant (∼200) values. © 1996 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition

Room temperature epitaxy of Pd films on GaN under conventional vacuum conditions

Q. Z. Liu, S. S. Lau, N. R. Perkins, and T. F. Kuech

Appl. Phys. Lett. 69, 1722 (1996); http://dx.doi.org/10.1063/1.118009 (3 pages) | Cited 17 times

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Pd films deposited at room temperature have been found to grow epitaxially on GaN grown by metalorganic vapor phase epitaxy (MOVPE). The Pd films were deposited on GaN substrates cleaned by chemicals only, and in a conventional e‐beam evaporation system with a vacuum of ∼1×10−7 Torr. MeV 4He backscattering spectrometry and the Read x‐ray camera were used to evaluate the Pd films. The effects of various chemical etchants—such as aqua regia, HCl:H2O, and HF:H2O—on the epitaxial quality of the Pd films have also been investigated. Ni and Pt films deposited on GaN in a similar manner were also found to be epitaxial. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Ct Interface structure and roughness

Ballistic electron emission microscopy in liquid helium using low dimensional collector electrodes

C. Eder, J. Smoliner, G. Strasser, and E. Gornik

Appl. Phys. Lett. 69, 1725 (1996); http://dx.doi.org/10.1063/1.118010 (3 pages) | Cited 8 times

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We report ballistic electron emission microscopy (BEEM) studies which show that a GaAs/AlGaAs heterostructure provides a very efficient collector electrode at 4.2 K. The enhanced thermal resolution at low temperature is utilized to determine the BEEM current threshold behavior very accurately. We find that diffusive scattering processes dominate the carrier transport across the Au/GaAs interface. Quantum wire regions on laterally structured samples are clearly identified with BEEM. The BEEM current is strongly enhanced on top of the quantum wires. © 1996 American Institute of Physics.
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73.40.Gk Tunneling
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
07.79.Cz Scanning tunneling microscopes

Improvement in low energy ion‐induced damage with a low temperature GaAs capping layer

Ching‐Hui Chen, Evelyn L. Hu, Umesh K. Mishra, James P. Ibbetson, Xuehua Wu, and Jim S. Speck

Appl. Phys. Lett. 69, 1728 (1996); http://dx.doi.org/10.1063/1.118011 (3 pages) | Cited 5 times

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A thin capping layer of annealed GaAs (∼210 Å) grown at low temperature (LT‐GaAs) can effectively block incident ions from penetrating into the growth substrate. Ion‐bombarded, multiple quantum well structures capped by an annealed LT‐GaAs layer show a dramatic improvement in the photoluminescence, compared to samples capped with ‘‘normal’’ GaAs. The improvement appears to be correlated with the microstructures of the LT‐GaAs, since the improvement is particularly notable for samples annealed at 600 °C. This improvement in low energy ion‐induced damage is primarily the result of the reduced channeling of ions through the LT‐GaAs layer. These results suggest a potential application of LT‐GaAs in reducing ion damage and underscore the importance of the microstructure of arsenic precipitates in LT‐GaAs layers. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.65.Cf Surface cleaning, etching, patterning
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