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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Reducing photorefractive effect in periodically poled ZnO- and MgO-doped LiNbO3 wavelength converters

Masaki Asobe, Osamu Tadanaga, Tsutomu Yanagawa, Hiroki Itoh, and Hiroyuki Suzuki

Appl. Phys. Lett. 78, 3163 (2001); http://dx.doi.org/10.1063/1.1374228 (3 pages) | Cited 20 times

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The photorefractive effect in annealed proton-exchanged waveguides in periodically poled nondoped, MgO- and ZnO-doped LiNbO3 was evaluated by monitoring the quasiphase matching (QPM) wavelength shift induced by a 0.784-μm-irradiating light. The QPM wavelength shift was reduced at room temperature by a factor of 3–6 in ZnO- and MgO-doped samples compared with the nondoped samples within a 104–105-W/cm2-irradiation intensity range. The doped samples exhibited no significant wavelength shifts when the temperature was raised to slightly above room temperature (50–60 °C). © 2001 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.65.Wi Nonlinear waveguides
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.79.Nv Optical frequency converters
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Generic degradation mechanism for 980 nm InxGa1−xAs/GaAs strained quantum-well lasers

S. N. G. Chu, N. Chand, W. B. Joyce, P. Parayanthal, and D. P. Wilt

Appl. Phys. Lett. 78, 3166 (2001); http://dx.doi.org/10.1063/1.1371967 (3 pages) | Cited 3 times

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We have observed In out diffusion from strained InxGa1−xAs quantum wells into the adjacent GaAs barriers in degraded 980-nm-wavelength strained quantum-well lasers. A previous calculation on misfit stress-induced compositional instability indicates that this material system is stable with respect to misfit strain. Therefore, the out diffusion of In from an InxGa1−xAs quantum well is mainly driven by the compositional discontinuity across the well/barrier heterointerfaces, and is believed to be activated by the nonradiative recombination of injected carriers. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
42.60.By Design of specific laser 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
68.35.Ct Interface structure and roughness
68.35.Gy Mechanical properties; surface strains

Time-resolved optical microscopy of a laser-based forward transfer process

D. Young, R. C. Y. Auyeung, A. Piqué, D. B. Chrisey, and Dana D. Dlott

Appl. Phys. Lett. 78, 3169 (2001); http://dx.doi.org/10.1063/1.1372200 (3 pages) | Cited 29 times

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Matrix-assisted pulsed laser evaporation direct write was investigated by ultrahigh speed optical microscopy. A composite barium–zirconium titanate/α-terpineol layer was irradiated by 355 nm laser pulses with a 150 ns pulse width, and it was observed that material removal does not begin until after the end of the pulse (t>200 ns) and continues for 1 μs after the irradiation. The desorption plume consists of micron-size particles moving with a velocity of ∼0.2 km/s. The slow response is attributed to the combination of particle absorbers and highly viscous fluid. The ability to form continuous, pinhole-free coatings is due to slow coalescence of the particles. © 2001 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
68.43.Tj Photon stimulated desorption
79.20.La Photon- and electron-stimulated desorption
78.47.-p Spectroscopy of solid state dynamics
42.62.Cf Industrial applications
07.60.Pb Conventional optical microscopes

3.6 mW blue light by direct frequency doubling of a diode laser using an aperiodically poled lithium niobate crystal

D. J. L. Birkin, E. U. Rafailov, G. S. Sokolovskii, W. Sibbett, G. W. Ross, P. G. R. Smith, and D. C. Hanna

Appl. Phys. Lett. 78, 3172 (2001); http://dx.doi.org/10.1063/1.1354160 (3 pages) | Cited 10 times

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3.6 mW blue (490 nm) light has been generated from a frequency-doubled, gain-switched InGaAs/GaAs diode laser using an aperiodically poled lithium niobate crystal. The matching of the crystal acceptance bandwidth to the laser spectral profile resulted in significant improvements to the conversion efficiency. © 2001 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.70.Mp Nonlinear optical crystals

Velocity control and staging in laser wakefield accelerators using segmented capillary discharges

D. Kaganovich, A. Zigler, R. F. Hubbard, P. Sprangle, and A. Ting

Appl. Phys. Lett. 78, 3175 (2001); http://dx.doi.org/10.1063/1.1373407 (3 pages) | Cited 13 times

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To achieve multi-GeV electron energies in the laser wakefield accelerator, it is necessary to propagate an intense laser pulse long distances in plasma channels while maintaining a proper phase with the accelerated electrons. We have demonstrated a method that allows control of the laser group velocity in long, multistage plasma channels. The control is achieved by modifying the index of refraction through a variation of the plasma density using a segmented capillary discharge. © 2001 American Institute of Physics.
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41.75.Jv Laser-driven acceleration
52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Photonic band-gap properties of opaline lattices of spherical colloids doped with various concentrations of smaller colloids

Byron Gates and Younan Xia

Appl. Phys. Lett. 78, 3178 (2001); http://dx.doi.org/10.1063/1.1374229 (3 pages) | Cited 29 times

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Monodispersed polystyrene beads have been organized into highly ordered, three-dimensional (3D) lattices using a self-assembly procedure recently demonstrated by our group. Such a 3D periodic structure consisting of high and low dielectric regions exhibits a pseudo-band gap (or a stop band) in the optical regime, with the position of this gap mainly determined by the size of the polymer beads. Doping of this 3D crystalline lattice with polymer beads of a smaller size was found to have a profound influence on the order (and thus the photonic band-gap properties) of the lattice. When the concentration of the dopant reached a certain level, phase segregation occurred which led to the formation of samples with relatively smaller domain sizes. In accordance, the attenuation (or rejection ratio) of the stop band also decreased monotonically as the doping level was increased. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.70.Jk Polymers and organics
82.70.Dd Colloids
78.40.Me Organic compounds and polymers
64.75.-g Phase equilibria

Photonic band gap properties of CdS-in-opal systems

A. Blanco, H. Míguez, F. Meseguer, C. López, F. López-Tejeira, and J. Sánchez-Dehesa

Appl. Phys. Lett. 78, 3181 (2001); http://dx.doi.org/10.1063/1.1370981 (3 pages) | Cited 21 times

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Silica opals are used as templates where CdS is infiltrated with the aim to build inverse structures with enhanced photonic band gap properties. A control on the degree of infiltration, from 0% to 100%, is attained. The band gap at L is studied finding that the width decreases and then recovers as a function of CdS infilling (from bare opal to fully loaded structure). This is well accounted for by theory based on two different modes for the growth of CdS inside the opal pores. A shell mode seems to govern the growth at low infiltration (less than 10%). High quality opal templates, appropriate sintering, and a high and uniform infiltration are required to ensure further optical characterization of the inverse systems. Only heavily loaded structures are apt to be inverted. The gap in the fully loaded and the inverse opal are, respectively, two and three times broader than in the starting opal. © 2001 American Institute of Physics.
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42.70.Qs Photonic bandgap materials

Single-polarization single-mode intraband guidance in supersquare photonic crystals fibers

Albert Ferrando and Juan José Miret

Appl. Phys. Lett. 78, 3184 (2001); http://dx.doi.org/10.1063/1.1353837 (3 pages) | Cited 11 times

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We present a two-dimensional (2D) photonic crystal structure exhibiting appealing guiding properties as an optical fiber. The structure can be regarded as a dislocation of a variant from a 2D square photonic crystal and shows a large photonic band gap for on-axis illumination. The introduction of an off-lattice hole in the structure acts as a defect and generates a highly anisotropic intraband guidance. The combination of very strong anisotropy and intraband guidance gives rise to a mechanism of polarization discrimination in optical fiber propagation that enables this guiding structure to operate as a single-polarization single-mode fiber over a wide wavelength window. © 2001 American Institute of Physics.
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42.81.Gs Birefringence, polarization
42.70.Qs Photonic bandgap materials
71.55.Ht Other nonmetals
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Observations of bi-Maxwellian and single Maxwellian electron energy distribution functions in a capacitively coupled radio-frequency plasmas by laser Thomson scattering

M. A. Mansour ElSabbagh, M.D. Bowden, K. Uchino, and K. Muraoka

Appl. Phys. Lett. 78, 3187 (2001); http://dx.doi.org/10.1063/1.1363695 (3 pages) | Cited 9 times

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Electron energy distribution functions in low-pressure capacitively coupled radio-frequency argon discharges were measured using the technique of laser Thomson scattering. It was found that the distribution functions changed from a bi-Maxwellian at lower pressures to a single Maxwellian at higher pressures. These measurements provide independent confirmation of probe measurements made in similar discharges. The electron temperature and density of the cold group of electrons were measured with an accuracy of better than 10%. © 2001 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.27.Gr Strongly-coupled plasmas
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Nanometer-scale measurements of photoabsorption spectra of individual defects in semiconductors

Akira Hida, Yutaka Mera, and Koji Maeda

Appl. Phys. Lett. 78, 3190 (2001); http://dx.doi.org/10.1063/1.1371960 (3 pages) | Cited 8 times

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Photoabsorption measurements using scanning tunneling microscopy, in which a modulated component of the tunneling current induced by a wavelength-variable chopped light is detected, were conducted for a cleaved surface of GaAs to demonstrate that a simple scheme enables nanometer-scale imaging of individual subsurface defects isolated in the crystal with fingerprints of photoabsorption spectra associated with them. The origin of the signal modulation and the image contrast formation mechanism are discussed in terms of photothermal expansion caused by nonradiative recombinations at the defect, photoinduced defect transformation, and an electrostatic surface potential change due to a charge alteration of the defect. © 2001 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.05.Ea III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.-y Defects and impurities in crystals; microstructure

Raman scattering test of single-wall carbon nanotube composites

V. G. Hadjiev, M. N. Iliev, S. Arepalli, P. Nikolaev, and B. S. Files

Appl. Phys. Lett. 78, 3193 (2001); http://dx.doi.org/10.1063/1.1373405 (3 pages) | Cited 60 times

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Raman spectroscopy is used to infer elastic properties of single-wall carbon nanotubes (SWNTs) in composites. This letter presents strain-induced frequency shift of tangential Raman active modes of SWNTs embedded in epoxy resin subjected to bending. Epoxy curing and sample extension in the tensile strength test are found to create residual strains on the SWNT ropes. We demonstrate that specimen compression in combination with the Raman microprobe technique provides a means for determining of these strains and hence load transfer effectiveness. © 2001 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
81.70.Fy Nondestructive testing: optical methods
81.05.Qk Reinforced polymers and polymer-based composites
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
78.30.-j Infrared and Raman spectra
78.67.Ch Nanotubes
81.07.De Nanotubes
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Index and density changes induced by proton radiation in lanthanum crown glass

A. Gusarov, D. Doyle, A. Hermanne, and F. Berghmans

Appl. Phys. Lett. 78, 3196 (2001); http://dx.doi.org/10.1063/1.1373411 (3 pages) | Cited 1 time

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We studied the refractive index and density changes in cerium-doped lanthanum crown glass irradiated in air with 38.5 MeV protons. At a low proton fluence, the index change is linear with dose, and reaches 2.4×10−5 at 2.7×1012 p/cm2 (0.65 Mrad dose). The rate of index change decreases with the proton fluence, but at high total dose (1014 p/cm2) radiation-induced surface dilatation and birefringence start to appear. Our results show that the present concept of radiation-hard optical glass should be revised and that a high dose of proton radiation can produce index changes sufficient for the fabrication of integrated optical devices. © 2001 American Institute of Physics.
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42.70.Ce Glasses, quartz
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.80.Jh Ion radiation effects
61.82.Ms Insulators
78.20.Fm Birefringence
81.40.Wx Radiation treatment (particle and electromagnetic)
61.43.Fs Glasses

Enhanced band-gap blueshift due to group V intermixing in InGaAsP multiple quantum well laser structures induced by low temperature grown InP

A. S. W. Lee, M. MacKenzie, D. A. Thompson, J. Bursik, B. J. Robinson, and G. C. Weatherly

Appl. Phys. Lett. 78, 3199 (2001); http://dx.doi.org/10.1063/1.1374231 (3 pages) | Cited 16 times

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Photoluminescence and cross-sectional transmission electron microscopy, combined with x-ray compositional analysis, have been used to study quantum well intermixing in an InGaAsP quantum well laser structure. Quantum well intermixing is induced by capping the samples with a layer of InP grown at low temperature (300 °C) and subjecting them to rapid thermal anneal treatments in the temperature range 600–800 °C. The presence of the low temperature InP layer, which contains an abundance of nonequilibrium point defects, significantly enhances the intermixing on annealing, producing a large band-gap blueshift. The microscopy results show good broadening with smeared interfaces, and the compositional analysis suggests this can be attributed to the intermixing of group V atoms. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
68.65.Fg Quantum wells
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.72.Cc Kinetics of defect formation and annealing
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Catalytic synthesis and photoluminescence of β-Ga2O3 nanowires

C. H. Liang, G. W. Meng, G. Z. Wang, Y. W. Wang, L. D. Zhang, and S. Y. Zhang

Appl. Phys. Lett. 78, 3202 (2001); http://dx.doi.org/10.1063/1.1374498 (3 pages) | Cited 107 times

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Monoclinic gallium oxide (β-Ga2O3) nanowires were synthesized by heat treating a composite material of GaAs and pre-evaporated Au at 1240 °C in dry oxygen atmosphere. The catalytic Au metal generated liquid nanoclusters that serve as reactive sites confining and directing the growth of β-Ga2O3 nanowires during the vapor-liquid-solid growth process. The β-Ga2O3 nanowires have diameters ranging from 20 to 50 nm and lengths of several micrometers. Photoluminescence measurement under excitation at 250 nm shows that the bulk β-Ga2O3 nanowires have a stable blue emission at 475 nm and an ultraviolet emission at 330 nm, which may be related to the defects such as the oxygen vacancy and the gallium–oxygen vacancy pair. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Stress engineering during metalorganic chemical vapor deposition of AlGaN/GaN distributed Bragg reflectors

K. E. Waldrip, J. Han, J. J. Figiel, H. Zhou, E. Makarona, and A. V. Nurmikko

Appl. Phys. Lett. 78, 3205 (2001); http://dx.doi.org/10.1063/1.1371240 (3 pages) | Cited 58 times

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In situ stress monitoring has been employed during metalorganic chemical vapor deposition of AlGaN/GaN distributed Bragg reflectors (DBRs). It was found that the insertion of multiple AlN interlayers is effective in converting the tensile growth stress typically observed in this system into compression, thus alleviating the problem of crack generation. Crack-free growth of a 60 pair Al0.20Ga0.80N/GaN quarter-wavelength DBR was obtained over the entire 2 in. wafer; an accompanying reflectivity of at least 99% was observed near the peak wavelength around 380 nm. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
42.55.Sa Microcavity and microdisk lasers
42.55.Px Semiconductor lasers; laser diodes

Melting of indium at high pressure determined by monochromatic x-ray diffraction in an externally-heated diamond anvil cell

Guoyin Shen, Nagayoshi Sata, Mark L. Rivers, and Stephen R. Sutton

Appl. Phys. Lett. 78, 3208 (2001); http://dx.doi.org/10.1063/1.1374497 (3 pages) | Cited 6 times

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The melting behavior of indium at high pressure has been studied in an externally heated diamond anvil cell (DAC) using x-ray diffraction measurements. Melting at high pressure was identified by the appearance of diffuse scattering from the melt with the simultaneous disappearance of crystalline diffraction signals. The observed melting curve is in good agreement with previous determinations based on resistivity measurements in a piston cylinder apparatus. These results demonstrate the successful melting experiments in a DAC using the x-ray diffuse scattering as the melting criterion. © 2001 American Institute of Physics.
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64.70.D- Solid-liquid transitions
62.50.-p High-pressure effects in solids and liquids
07.35.+k High-pressure apparatus; shock tubes; diamond anvil cells
61.05.cf X-ray scattering (including small-angle scattering)

Influence of electronic temperature and distribution on the second-order surface nonlinear susceptibility of metals

Chunlei Guo, George Rodriguez, Mark Hoffbauer, and Antoinette J. Taylor

Appl. Phys. Lett. 78, 3211 (2001); http://dx.doi.org/10.1063/1.1374517 (3 pages) | Cited 3 times

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We performed ultrafast, optical pump and second-harmonic-generation (SHG) probe measurements to study the effects of electronic temperature (Te) and distribution on the second-order nonlinear susceptibility [χ(2)] for a gold surface. These measurements clarify the physical origin of the recently observed power-law deviation of the SHG signal at high illuminating intensities. The study of SHG is extended to the high Te regime, and the results agree with a model calculation presented in this letter. The consistency between the experimental and theoretical results in this letter provides a uniform picture of the effects of the electronic temperature and distribution on χ(2). © 2001 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.68.+m Optical properties of surfaces
78.66.Bz Metals and metallic alloys
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.47.-p Spectroscopy of solid state dynamics

Staircase-like spectral dependence of ground-state luminescence time constants in high-density InAs/GaAs quantum dots

Yu. I. Mazur, J. W. Tomm, V. Petrov, G. G. Tarasov, H. Kissel, C. Walther, Z. Ya. Zhuchenko, and W. T. Masselink

Appl. Phys. Lett. 78, 3214 (2001); http://dx.doi.org/10.1063/1.1371965 (3 pages) | Cited 23 times

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Time-resolved photoluminescence (PL) from InAs/GaAs quantum dots with a bimodal size distribution is used to investigate the dynamic carrier-transfer processes which couple transfer between similarly sized quantum dots and between quantum dots in different size categories. The relationship between the decay time and the emission energy appears staircaselike and the energetic positions of the steps as well as the shape can be correlated to the shape of the steady-state PL emission through a rate-equation theory. These results show how transient PL can be used to investigate the dynamics of carrier transfer in quantum-dot systems. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.21.La Quantum dots
78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.47.-p Spectroscopy of solid state dynamics

Direct evidence for implanted Fe on substitutional Ga sites in GaN

U. Wahl, A. Vantomme, G. Langouche, J. G. Correia, and L. Peralta

Appl. Phys. Lett. 78, 3217 (2001); http://dx.doi.org/10.1063/1.1372201 (3 pages) | Cited 10 times

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The lattice location of iron in thin-film, single-crystalline hexagonal GaN was studied by means of the emission channeling technique. Following 60 keV room temperature implantation of the precursor isotope 59Mn at a dose of 1.0×1013 cm−2 and annealing up to 900 °C, the angular distribution of β− particles emitted by the radioactive isotope 59Fe was measured by a position-sensitive electron detector. The β− emission patterns around the [0001], [math102], [math101], and [math113] directions give direct evidence that the majority of Fe (80%) occupies substitutional Ga sites. © 2001 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.72.S- Impurities in crystals
71.55.Eq III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing

Multiwavelength thermal lens determination of fluorescence quantum efficiency of solids: Application to Nd3+-doped fluoride glass

S. M. Lima, A. A. Andrade, R. Lebullenger, A. C. Hernandes, T. Catunda, and M. L. Baesso

Appl. Phys. Lett. 78, 3220 (2001); http://dx.doi.org/10.1063/1.1375000 (3 pages) | Cited 31 times

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A multiwavelength thermal lens (TL) method was developed to determine the fluorescence quantum efficiency of solids. The experiments have been performed in Nd3+-doped fluoride glasses, using five different excitation wavelengths: 514, 576, 741, 796, and 867 nm. In this work, the absolute value of fluorescence quantum efficiency can be obtained by the linear dependence of the TL signal with the excitation wavelength. Our results suggest that the method can be applied to study a wide range of fluorescent materials, with a special ability to be used for measurements of highly transparent materials with very low TL effect. © 2001 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
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Band gap engineering of thin-film electroluminescent devices

Alexey N. Krasnov

Appl. Phys. Lett. 78, 3223 (2001); http://dx.doi.org/10.1063/1.1374236 (3 pages) | Cited 1 time

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We introduce an alternative concept to increase the efficiency and brightness of thin-film electroluminescent (TFEL) devices. The method utilizes band gap engineering of the active layer of the device. The initial steps of our work using a ZnSxSe1−x alloy are also presented to demonstrate the workability of the method. This letter discusses the related obstacles and future potentials of the band gap engineering for monochrome and color TFEL devices. © 2001 American Institute of Physics.
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85.60.Pg Display systems
78.60.Fi Electroluminescence
71.20.Nr Semiconductor compounds
78.66.Hf II-VI semiconductors

Fabrication of GaN suspended microstructures

R. P. Strittmatter, R. A. Beach, and T. C. McGill

Appl. Phys. Lett. 78, 3226 (2001); http://dx.doi.org/10.1063/1.1364504 (3 pages) | Cited 12 times

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We report on a versatile processing technology for the fabrication of micro-electromechanical systems in gallium nitride (GaN). This technology, which is an extension of photo-electrochemical etching, allows for the controlled and rapid undercutting of p-GaN epilayers. The control is achieved through the use of opaque metal masks to prevent etching in designated areas, while the high lateral etch rates are achieved by biasing the sample relative to the solution. For GaN microchannel structures processed in this way, undercutting rates in excess of 30 μm/min have been attained. We propose two mechanisms to account for these high etch rates. © 2001 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning

Field emission from GaN surfaces roughened by hydrogen plasma treatment

Takashi Sugino, Takamitsu Hori, Chiharu Kimura, and Tomohide Yamamoto

Appl. Phys. Lett. 78, 3229 (2001); http://dx.doi.org/10.1063/1.1370979 (3 pages) | Cited 45 times

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GaN layers are grown on sapphire substrates with AlN buffer layers by the metalorganic chemical vapor deposition method. GaN layers are doped with Si. The electron density of the n-type GaN is 2×1017 cm−3. It is found that the GaN surface is etched with hydrogen (H2) plasma produced by supplying microwave power leading to the formation of the roughened surface of GaN. A variation in the surface morphology occurs due to microwave power and gas pressure. Field emission measurements are carried out for GaN with various surface morphologies. It is observed that the turn-on electric field decreases with increasing surface roughness of the GaN. A turn-on electric field of the electron emission is estimated to be as low as 12.4 V/μm. © 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.Ea III-V semiconductors
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

High peak-to-valley ratios observed in InAs/InP resonant tunneling quantum dot stacks

M. Borgstrom, T. Bryllert, T. Sass, B. Gustafson, L.-E. Wernersson, W. Seifert, and L. Samuelson

Appl. Phys. Lett. 78, 3232 (2001); http://dx.doi.org/10.1063/1.1374235 (3 pages) | Cited 22 times

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Resonant tunneling was observed through single InAs quantum dot (QD) stacks embedded in InP barriers with peak-to-valley ratios as high as 85 at 7 K. Negative differential resistance in the current–voltage [I(V)] characteristics was obtained up to a point above the temperature of liquid nitrogen. These features were observed in measurements on low-density QD stacks, in which a macroscopic ohmic contact covered less than 150 QD stacks. Due to the design of the structure, the upper QD in the stack has the function of a zero-dimensional emitter. Electrons easily fill the upper dot, whereas tunneling through the entire structure is only allowed when two states in the dots align energetically, resulting in sharp resonant tunneling peaks with high peak-to-valley ratios. © 2001 American Institute of Physics.
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73.23.Hk Coulomb blockade; single-electron tunneling
73.21.La Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots

Mechanical deformation of InP and GaAs by spherical indentation

J. E. Bradby, J. S. Williams, J. Wong-Leung, M. V. Swain, and P. Munroe

Appl. Phys. Lett. 78, 3235 (2001); http://dx.doi.org/10.1063/1.1372207 (3 pages) | Cited 46 times

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The mechanical deformation by spherical indentation of both crystalline InP and GaAs was characterized using cross-sectional transmission electron microscopy (XTEM) and atomic force microscopy. All load–unload curves show a discontinuity (or “pop in”) during loading. Slip bands oriented along {111} planes are visible in XTEM micrographs from residual indentations in both materials and no evidence of any phase transformations was found. Higher load indentations (35 mN for InP and 50 mN for GaAs) also revealed subsurface cracking. In contrast no cracking was found beneath a 25 mN InP indent although the hardness and modulus data are almost identical to those of the cracked sample. The subsurface cracks are thought to be nucleated by high stress concentrations caused by dislocation pileup. © 2001 American Institute of Physics.
Show PACS
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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