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27 Aug 2001

Volume 79, Issue 9, pp. 1225-1402

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Midinfrared surface-emitting PbSe/PbEuTe quantum-dot lasers

G. Springholz, T. Schwarzl, W. Heiss, G. Bauer, M. Aigle, H. Pascher, and I. Vavra

Appl. Phys. Lett. 79, 1225 (2001); http://dx.doi.org/10.1063/1.1389517 (3 pages) | Cited 27 times

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Midinfrared laser emission from self-organized PbSe quantum dots in a high-finesse vertical-cavity surface-emitting laser structure is reported. The structure was grown by molecular-beam epitaxy and consists of high reflectivity epitaxial EuTe/PbEuTe Bragg mirrors with a PbSe/Pb1−xEuxTe quantum-dot superlattice as the active region. Narrow laser emission at 4.2–3.9 μm induced by optical pumping is achieved at temperatures up to 90 K. The observation of simultaneous two-mode emission indicates a width of the inhomogeneously broadened PbSe dot gain spectrum of about 18 meV. © 2001 American Institute of Physics.
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42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors

Periodic nanostructure array in crossed holographic gratings on silica glass by two interfered infrared-femtosecond laser pulses

Ken-ichi Kawamura, Nobuhiko Sarukura, Masahiro Hirano, Naoko Ito, and Hideo Hosono

Appl. Phys. Lett. 79, 1228 (2001); http://dx.doi.org/10.1063/1.1398618 (3 pages) | Cited 25 times

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Two cross-superposed holographic gratings were encoded on silica glass by femtosecond laser pulses (wavelength ∼800 nm). A variety of periodic nanostructures from a one-dimensional wire array to two-dimensional arrays of holes or islands were formed by changing the energy density and the incidence angle of the irradiation laser beams. The smallest dimensions were a width of ∼15 nm for wires and a diameter of ∼20 nm for holes. Laser-driven microexplosions occurring within the microcylindrical-lens array created by the first laser pulse are suggested as a mechanism for the formation of these structures. Only two pulses are required to encode these periodic structures, which are applicable to emerging nanostructured devices such as photonic crystals and quantum dot or wire arrays. © 2001 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
42.62.-b Laser applications
42.70.Ce Glasses, quartz

Development of high-performance blue–violet-emitting organic electroluminescent devices

Kenji Okumoto and Yasuhiko Shirota

Appl. Phys. Lett. 79, 1231 (2001); http://dx.doi.org/10.1063/1.1398325 (3 pages) | Cited 28 times

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Two high-performance blue-violet-emitting organic electroluminescent devices with electroluminescence peaking at 404 and 415 nm were developed using a hole-blocking amorphous molecular material, 1,3,5-tris(4-fluorobiphenyl-4′-yl)benzene, and emitting amorphous molecular materials, N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine and N,N′-di(4-biphenylyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine. The devices show maximum luminaces of 3960 cd m−2 at 15 V and 2550 cd m−2 at 12.0 V, having turn-on voltages of 4.0 V and external quantum efficiencies of 1.40% and 1.25%. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Production of relativistic electrons by irradiation of 43-fs-laser pulses on copper film

Yuji Oishi, Takuya Nayuki, Koshichi Nemoto, Yasuaki Okano, Yoichiro Hironaka, Kazutaka G. Nakamura, and Ken-ichi Kondo

Appl. Phys. Lett. 79, 1234 (2001); http://dx.doi.org/10.1063/1.1396311 (3 pages) | Cited 18 times

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The energy spectra of fast electrons produced by ultrashort, high-intensity laser pulses were directly measured using a magnetic spectrometer with an imaging plate. The typical temperature was 350 keV for irradiation on 30 μm thick copper film by pulses of width 43 fs, intensity 2.7×1018 W/cm2, repetition rate 10 Hz without artificial prepulses and was found to be close to the ponderomotive potential. In addition, the energy spectra of high-energy photons, which are expected to be produced from the electrons, were calculated. © 2001 American Institute of Physics.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.66.Bz Metals and metallic alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
78.47.-p Spectroscopy of solid state dynamics
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Observation of pinching in the compact toroid injection experiment: Implications for a plasma opening switch

K. L. Baker, D. Q. Hwang, R. W. Evans, R. D. Horton, H. S. McLean, and S. D. Terry

Appl. Phys. Lett. 79, 1237 (2001); http://dx.doi.org/10.1063/1.1400773 (3 pages) | Cited 2 times

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A compact toroid inductively stores the energy released by a capacitor bank as it is being accelerated. This energy can be stored for a period of more than ten microseconds and then transferred to a load on a much shorter time scale. This article presents framing camera images of the radial compression of plasma trailing behind a compact toroid as the compact toroid leaves its inner electrode. This compression illustrates the basic principles of a compact toroid plasma opening switch which could be used to drive fast z pinches. © 2001 American Institute of Physics.
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52.55.Ip Spheromaks
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.75.Kq Plasma switches (e.g., spark gaps)
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion

Xenon excimer emission from pulsed microhollow cathode discharges

M. Moselhy, W. Shi, R. H. Stark, and K. H. Schoenbach

Appl. Phys. Lett. 79, 1240 (2001); http://dx.doi.org/10.1063/1.1397760 (3 pages) | Cited 27 times

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By applying electrical pulses of 20 ns duration to xenon microplasmas, generated by direct current microhollow cathode discharges, we were able to increase the xenon excimer emission by more than an order of magnitude over direct current discharge excimer emission. For pulsed voltages in excess of 500 V, the optical power at 172 nm was found to increase exponentially with voltage. Largest values obtained were 2.75 W of vacuum-ultraviolet optical power emitted from a single microhollow cathode discharge in 400 Torr xenon with a 750 V pulse applied to a discharge. Highest radiative emittance was 15.2 W/cm2. The efficiency for excimer emission was found to increase linearly with pulsed voltages above 500 V reaching values of 20% at 750 V. © 2001 American Institute of Physics.
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42.72.Bj Visible and ultraviolet sources
52.80.Hc Glow; corona
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Photoluminescence from quantum dots in cubic GaN/InGaN/GaN double heterostructures

O. Husberg, A. Khartchenko, D. J. As, H. Vogelsang, T. Frey, D. Schikora, K. Lischka, O. C. Noriega, A. Tabata, and J. R. Leite

Appl. Phys. Lett. 79, 1243 (2001); http://dx.doi.org/10.1063/1.1396314 (3 pages) | Cited 26 times

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We have measured photoluminescence spectra of molecular-beam-epitaxy-grown cubic GaN/InxGa1−xN/GaN double heterostructures with x between 0.09 and 0.33. We observe a luminescence peak at about 2.3–2.4 eV which is almost independent of the InGaN layer composition. High-resolution x-ray diffraction measurements revealed a pseudomorphic In-rich phase with x = 0.56±0.02 embedded in the InGaN layers. Including strain effects we calculate a gap energy Eg = 2.13 eV of this phase. In cubic InGaN, spontaneous polarization and strain-induced piezoelectric fields are negligible. Therefore, the observed difference between the luminescence energy and the gap of the In-rich phase is assumed to be due to the localization of excitons at quantum-dot-like structures with a size of about 15 nm. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Pulsed liquid-injection metalorganic chemical vapor deposition of (La0.7Sr0.3MnO3/SrTiO3)15 superlattices

C. Dubourdieu, M. Rosina, H. Roussel, F. Weiss, J. P. Sénateur, and J. L. Hodeau

Appl. Phys. Lett. 79, 1246 (2001); http://dx.doi.org/10.1063/1.1398607 (3 pages) | Cited 16 times

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(La0.7Sr0.3MnO3/SrTiO3)15 superlattices have been grown by pulsed liquid-injection metalorganic chemical vapor deposition on monocrystalline substrates such as LaAlO3, SrTiO3, and MgO. The pulsed-injection technique allows one to control precisely the amount of precursors delivered to the deposition chamber and thus the thickness of each individual layer. The period of the superlattices depends indeed linearly on the number of injected droplets. In our deposition conditions, the average growth rates are ∼0.130 nm/injection for La0.7Sr0.3MnO3 and 0.042 nm/injection for SrTiO3, with no significant difference as regard to the substrate used. The strain’s state of the superlattices depends on the relative thicknesses of the La0.7Sr0.3MnO3 and SrTiO3 layers and also on the substrate used. Finally, the deposition of superlattices with ultrathin interlayers of few unit cells has been demonstrated. © 2001 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
68.65.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Ct Interface structure and roughness
68.65.Cd Superlattices
68.35.Gy Mechanical properties; surface strains

Optical gain in Si/SiO2 lattice: Experimental evidence with nanosecond pulses

Leonid Khriachtchev, Markku Räsänen, Sergei Novikov, and Juha Sinkkonen

Appl. Phys. Lett. 79, 1249 (2001); http://dx.doi.org/10.1063/1.1391406 (3 pages) | Cited 84 times

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Experimental evidence of population inversion and amplified spontaneous emission was found for Si nanocrystallites embedded in SiO2 surrounding under pumping with 5 ns light pulses at 380, 400, and 500 nm. As an important property, our experiments show a short lifetime of the population inversion allowing a generation of short (a few nanosecond) amplified light pulses in the Si/SiO2 lattice. The estimate for optical gain in the present samples is 6 cm−1 at 720 nm. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.Hj Laser materials
78.45.+h Stimulated emission
78.55.Ap Elemental semiconductors
61.46.-w Structure of nanoscale materials
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Grapevine-like growth of single walled carbon nanotubes among vertically aligned multiwalled nanotube arrays

Anyuan Cao, Xianfeng Zhang, Cailu Xu, Ji Liang, Dehai Wu, Xihua Chen, Bingqing Wei, and P. M. Ajayan

Appl. Phys. Lett. 79, 1252 (2001); http://dx.doi.org/10.1063/1.1399005 (3 pages) | Cited 17 times

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Large arrays of self-oriented, multiwalled carbon nanotubes (MWNTs) have been obtained by chemical vapor deposition. It has so far been impossible to translate this idea for growing single walled nanotubes (SWNTs) but we show here that oriented growth of SWNTs among vertically aligned MWNT arrays can be realized by the catalytic pyrolysis of ferrocene and xylene. The MWNTs act as the support structures for SWNTs, forcing them to grow upward steadily, like grapevines. The growth of vertically aligned SWNT over large areas brings about the possibility of exploring their properties in select configurations. © 2001 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Be Chemical synthesis methods
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

CoPt/Ag nanocomposites with (001) texture

V. Karanasos, I. Panagiotopoulos, D. Niarchos, H. Okumura, and G. C. Hadjipanayis

Appl. Phys. Lett. 79, 1255 (2001); http://dx.doi.org/10.1063/1.1397762 (3 pages) | Cited 26 times

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CoPt/Ag nanocomposites with the tetragonal (L10) structure have been prepared by magnetron sputtering. The dependence of texture on film thickness, bilayer thickness, CoPt volume fraction, and annealing conditions is investigated. Films with a thickness below 15 nm consist of islands with (001) texture while as the thickness increases, the islands coalesce into a continuous film and the (111) texture appears. Microstrain is minimized in the range of film thickness where the (001) texturing is optimum indicating that strain energy provides the driving force of (001) growth texturing. The (001) texture improves with CoPt volume fraction for all annealing times but disappears above 95 vol % indicating that the existence of the Ag plays an important role in the development of the (001) texture. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
75.50.Ss Magnetic recording materials
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Annealing effects on the microstructure of Ge/Si(001) quantum dots

X. Z. Liao, J. Zou, D. J. H. Cockayne, J. Wan, Z. M. Jiang, G. Jin, and Kang L. Wang

Appl. Phys. Lett. 79, 1258 (2001); http://dx.doi.org/10.1063/1.1398615 (3 pages) | Cited 10 times

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Ge/Si(001) multilayer islands produced by gas-source molecular-beam epitaxy at 575 °C were investigated using energy-filtering transmission electron microscopy. Results show, for as-grown samples, not only a continuous enlargement of island size in upper layers but also a continuous increase of Ge concentration within islands in upper layers. As a result of the increasing island size and Ge concentration within the islands, the island density in upper layers decreases. For samples annealed at 900 °C for 5 min, the aspect ratio of buried islands increases significantly, and the average Ge concentration within islands of different layers becomes uniform. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.37.Lp Transmission electron microscopy (TEM)

Selective area metalorganic vapor phase epitaxy of thick crack-free GaN films on trenched SiC substrates

Tetsuya Akasaka, Seigo Ando, Toshio Nishida, Hisao Saito, and Naoki Kobayashi

Appl. Phys. Lett. 79, 1261 (2001); http://dx.doi.org/10.1063/1.1394725 (3 pages) | Cited 4 times

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Crack-free GaN films up to 11-μm-thick have been grown by using trenched SiC substrates and selective area metalorganic vapor phase epitaxy. These crack-free GaN films have hexagonal shapes and are surrounded by trenches. 97% of the hexagonal GaN films with side lengths of 100 μm and thickness of 11 μm was crack-free. The GaN films do not crack because the lateral propagation of cracks stops at the trenches and strain is relaxed in the small-area hexagonal GaN. This strain relaxation is confirmed by micro-Raman scattering measurements and agrees well with theoretical predictions. © 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.)
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Void formation by thermal stress concentration at twin interfaces in Cu thin films

A. Sekiguchi, J. Koike, S. Kamiya, M. Saka, and K. Maruyama

Appl. Phys. Lett. 79, 1264 (2001); http://dx.doi.org/10.1063/1.1399021 (3 pages) | Cited 33 times

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A void formation mechanism was investigated in an electroplated copper thin film on Ta/SiO2/Si. Microstructural observation after thermal cycling indicated that void formation occurred at intersecting points or terminating corners of annealing twins. The calculated stress distribution was compared with experimental results of the void formation tendency. An excellent correlation was found between void formation sites and stress concentration sites. Electron diffraction analysis revealed that most twin interfaces in Cu thin films are incoherent {322} planes. The stress concentration drives diffusion along incoherent twin interfaces of {322} and leads to void formation at twin interfaces and corners. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties
61.72.Qq Microscopic defects (voids, inclusions, etc.)
85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Cc Kinetics of defect formation and annealing
61.72.Mm Grain and twin boundaries

Molecular dynamics simulation of the meniscus formation between two surfaces

Yunfei Chen, Jian-gang Weng, Jennifer R. Lukes, Arunava Majumdar, and Chang-Lin Tien

Appl. Phys. Lett. 79, 1267 (2001); http://dx.doi.org/10.1063/1.1394957 (3 pages) | Cited 5 times

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The molecular dynamics computational method is used to simulate meniscus formation around an asperity in a rough surface represented as a sinusoidal wave. Simulation results show that the meniscus formation depends on the interaction potential between the solid wall and the liquid atoms. For completely and partially dry substrates a meniscus cannot form around an asperity. For partially and completely wetting substrates the asperity helps to adsorb the fluid atoms and form a meniscus. These simulation results confirm that if the film thickness exceeds a critical value, the capillary pressure contributes strongly to stiction. © 2001 American Institute of Physics.
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68.08.Bc Wetting

Self-doping near the seed/layer interface in conformal GaAs layers grown on Si

A. M. Ardila, O. Martínez, M. Avella, J. Jiménez, B. Gérard, J. Napierala, and E. Gil-Lafon

Appl. Phys. Lett. 79, 1270 (2001); http://dx.doi.org/10.1063/1.1399008 (3 pages) | Cited 3 times

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Undoped GaAs layers grown on Si substrates by the conformal method were studied by micro-Raman spectroscopy, cathodoluminescence, and diluted Sirtl solution with light (DSL) etching. The results show that nonintentional doping of conformal layers can take place near the seed/layer interface. The self-doped area presents a bright luminescence emission and shows longitudinal optic-plasmon coupled Raman modes. The nonintentional dopants were n type as deduced from Raman spectroscopy and DSL selective etching. The doped region extends only 2–3 μm from the seed and was tentatively associated with enhanced diffusion of Si in the presence of dislocations at the interface between the seed and the conformal layer. © 2001 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.30.Fs III-V and II-VI semiconductors
63.20.kk Phonon interactions with other quasiparticles

Binding energy of vacancy clusters generated by high-energy ion implantation and annealing of silicon

V. C. Venezia, L. Pelaz, H.-J. L. Gossmann, T. E. Haynes, and C. S. Rafferty

Appl. Phys. Lett. 79, 1273 (2001); http://dx.doi.org/10.1063/1.1385192 (3 pages) | Cited 7 times

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We have measured the evolution of the excess-vacancy region created by a 2 MeV, 1016/cm2 Si implant in the silicon surface layer of silicon-on-insulator substrates. Free vacancy supersaturations were measured with Sb dopant diffusion markers during postimplant annealing at 700, 800, and 900 °C, while vacancy clusters were detected by Au labeling. We demonstrate that a large free vacancy supersaturation exists for short times, during the very early stages of annealing between the surface and the buried oxide (1 μm below). Afterwards, the free vacancy concentration returns to equilibrium in the presence of vacancy clusters. These vacancy clusters form at low temperatures and are stable to high temperatures, i.e., they have a low formation energy and high binding energy. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect

Conductive phosphate and fluorophosphate glasses with fullerene doping

Heping Zeng, Fucheng Lin, Sen Mao, and Zhizhan Xu

Appl. Phys. Lett. 79, 1276 (2001); http://dx.doi.org/10.1063/1.1394165 (3 pages) | Cited 1 time

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The appropriate amount of fullerene doping in phosphate and fluorophosphate optical glasses modifies the structures of glass matrices by bonding the nearby -[PO4]- tetrahedra with nonbridging oxygen anions, and consequently building up observable conductivity at room temperature. Non-Arrhenius ionic conductivity is observed, which is interpreted as a result of the temperature dependence of the activation energies of the mobile cations. The variation of microphotoluminescence induced by the electric field presents us with an indirect way to characterize the random activation, percolation migration, and retrap of metal cations near fullerene-related amorphous islands. © 2001 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
42.70.Ce Glasses, quartz
61.43.Fs Glasses

Inter-conduction band electron relaxation dynamics in 6H–SiC

T. Tomita, S. Saito, T. Suemoto, H. Harima, and S. Nakashima

Appl. Phys. Lett. 79, 1279 (2001); http://dx.doi.org/10.1063/1.1399304 (3 pages) | Cited 6 times

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The ultrafast inter-conduction band carrier dynamics in 6H–SiC was observed by using pump and probe transient absorption technique. Probe wavelength dependence of the bleaching was compared with the steady-state absorption profiles for polarizations parallel and perpendicular to the c axis, and these bleachings were ascribed to the decrease of electron populations in the lowest conduction band. The relaxation time from the higher to the lowest conduction band due to the inter-conduction band electron–phonon scattering is 1.25 ps. © 2001 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
63.20.K- Phonon interactions
78.40.Fy Semiconductors
72.80.Jc Other crystalline inorganic semiconductors

Strain effects on exciton resonance energies of ZnO epitaxial layers

T. Makino, T. Yasuda, Y. Segawa, A. Ohtomo, K. Tamura, M. Kawasaki, and H. Koinuma

Appl. Phys. Lett. 79, 1282 (2001); http://dx.doi.org/10.1063/1.1398328 (3 pages) | Cited 50 times

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Magnitudes of strain in ZnO epitaxial layers grown on sapphire(0001) substrates under various growth conditions were experimentally determined by x-ray diffraction. We discuss the strain-induced energy shift on the exciton resonances, the results of which were analyzed theoretically using the Hamiltonian for the valence bands under in-plain biaxial strain. Comparative studies with GaN evidenced the advantages of ZnO in terms of sensitivity of the strain-induced energy shift and of piezoelectric effect in heterostructures. © 2001 American Institute of Physics.
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78.66.Hf II-VI semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
68.60.Bs Mechanical and acoustical properties
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds
68.55.A- Nucleation and growth
77.65.Ly Strain-induced piezoelectric fields
68.65.Fg Quantum wells
78.67.De Quantum wells
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Study of exciton–longitudinal optical phonon coupling in quantum wells for optoelectronic applications

W. Z. Shen

Appl. Phys. Lett. 79, 1285 (2001); http://dx.doi.org/10.1063/1.1392306 (3 pages) | Cited 3 times

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The study of exciton–longitudinal optical (LO) phonon coupling in semiconductor quantum well (QW) structures and their corresponding bulk materials reveals four distinct features: a large difference between (i) III–V and II–VI QW structures, (ii) multiple QW and single QW structures, as well as (iii) QW structures and their corresponding bulk materials, and its linear dependence on well width in QW structures. A quantitatively theoretical approach is presented, which can explain well all the experimental observations and can clarify the controversy in the literature. The effects of alloy disorder and strain in QW structures on exciton–LO phonon coupling are also discussed. © 2001 American Institute of Physics.
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73.21.Fg Quantum wells
78.67.De Quantum wells
63.20.kk Phonon interactions with other quasiparticles
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.66.Hf II-VI semiconductors

Effect of surface roughness on field emission from chemical vapor deposited polycrystalline diamond

N. Koenigsfeld, R. Kalish, A. Cimmino, D. Hoxley, S. Prawer, and I. Yamada

Appl. Phys. Lett. 79, 1288 (2001); http://dx.doi.org/10.1063/1.1383803 (3 pages) | Cited 11 times

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The effect of surface roughness on electron emission from hydrogenated polycrystalline diamond films is reported. Field emission measurements were performed with both millimeter and nanometer spatial resolution using scanning probe techniques. Surface asperities were removed by ion beam treatment, which resulted in a reduction of the rms roughness from 198 to 94 nm, leading to an increase in the threshold field required for electron emission by about a factor of 2. These results suggest that surface asperities, rather than grain boundaries, are the dominant influence on electron emission in polycrystalline diamond films. © 2001 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
79.70.+q Field emission, ionization, evaporation, and desorption
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Ultrafast carrier trapping in microcrystalline silicon observed in optical pump–terahertz probe measurements

P. Uhd Jepsen, W. Schairer, I. H. Libon, U. Lemmer, N. E. Hecker, M. Birkholz, K. Lips, and M. Schall

Appl. Phys. Lett. 79, 1291 (2001); http://dx.doi.org/10.1063/1.1394953 (3 pages) | Cited 29 times

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We report on direct evidence of ultrafast carrier dynamics displaying features on the picosecond time scale in microcrystalline silicon (μc-Si:H). The dynamics of photogenerated carriers is studied by using above-band-gap optical excitation and probing the instantaneous carrier mobility and density with a THz pulse. Within the first picoseconds after excitation, the THz transmission transients show a fast initial decay of the photoinduced absorption followed by a slower decrease due to carrier recombination. We propose that the initial fast decay in the THz transients is due to carrier capture in the trapping states. © 2001 American Institute of Physics.
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72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Fr Low-field transport and mobility; piezoresistance
72.40.+w Photoconduction and photovoltaic effects
81.05.Cy Elemental semiconductors
78.47.-p Spectroscopy of solid state dynamics

Enhanced As–Sb intermixing of GaSb monolayer superlattices in low-temperature grown GaAs

V. V. Chaldyshev, N. A. Bert, Yu. G. Musikhin, A. A. Suvorova, V. V. Preobrazhenskii, M. A. Putyato, B. R. Semyagin, P. Werner, and U. Gösele

Appl. Phys. Lett. 79, 1294 (2001); http://dx.doi.org/10.1063/1.1394166 (3 pages) | Cited 9 times

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As–Sb compositional intermixing was studied by transmission electron microscopy (TEM) in GaAs films grown by molecular-beam epitaxy at low temperature (LT) and δ doped with antimony. The TEM technique was calibrated by imaging the as-grown films with δ layers containing various amounts of Sb. The calibration allowed us to deduce the effective As–Sb interdiffusion coefficient from apparent thickness of the Sb δ layers in the films subjected to isochronal anneals at 400–600 °C. The As–Sb intermixing in LT GaAs was found to be much enhanced when compared to conventional material. Its temperature dependence yields a diffusion coefficient of DAs–Sb = 2×10−14 exp(−0.62±0.15 eV/kt) cm2 s−1. Since the kick-out mechanism operating under equilibrium conditions is valid for As–Sb interdiffusion in GaAs, the enhanced intermixing was attributed to an oversaturation of arsenic self-interstitials in the LT GaAs films. The effective activation energy for As–Sb interdiffusion in LT GaAs seems to be reasonably close to the migration enthalpy of As interstitials, whereas their concentration was roughly estimated as 1018 cm−3. © 2001 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.Ny Chemical interdiffusion; diffusion barriers
68.65.Cd Superlattices
68.37.Lp Transmission electron microscopy (TEM)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Γ–L–X mixed symmetry of nitrogen-induced states in GaAs1−xNx probed by resonant Raman scattering

M. J. Seong, A. Mascarenhas, and J. F. Geisz

Appl. Phys. Lett. 79, 1297 (2001); http://dx.doi.org/10.1063/1.1399010 (3 pages) | Cited 14 times

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A resonant Raman scattering study near the nitrogen-induced E+ state in GaAs1−xNx at 80 K with special emphasis on all the zone-boundary phonons is used to investigate the full symmetry of the E+ state. We have observed that various phonons at the L- and X-zone boundaries not only emerge as strong and sharp Raman features for excitations near the E+ transition but also exhibit the same intensity resonance enhancement as observed for the zone center phonons, longitudinal-optical (Γ) and transverse-optical (Γ). Our data provide strong evidence of significant L and X components in the wave function of the nitrogen-induced E+ state in GaAs1−xNx. © 2001 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
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