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4 Jan 1999

Volume 74, Issue 1, pp. 1-158

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Near-threshold gain mechanisms in GaN thin films in the temperature range of 20–700 K

S. Bidnyk, T. J. Schmidt, B. D. Little, and J. J. Song

Appl. Phys. Lett. 74, 1 (1999); http://dx.doi.org/10.1063/1.123114 (3 pages) | Cited 40 times

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We report the results of an experimental study on near-threshold gain mechanisms in optically pumped GaN epilayers in the temperature range of 20–700 K. High-quality single-crystal GaN films grown on 6H–SiC and (0001) sapphire were used in this study. We show that the dominant near-threshold gain mechanism is inelastic exciton–exciton scattering for temperatures below ∼150 K, characterized by band-filling phenomena and a low stimulated emission (SE) threshold. An analysis of both the temperature dependence of the SE threshold and the relative shift between stimulated and band-edge-related emission indicates electron–hole plasma is the dominant gain mechanism for temperatures exceeding 150 K. Based on our results, we discuss possibilities of reducing the room-temperature lasing threshold in laser diode structures with a GaN active medium. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.45.+h Stimulated emission
42.55.Px Semiconductor lasers; laser diodes
71.35.Gg Exciton-mediated interactions
73.50.Mx High-frequency effects; plasma effects

Heterodyning far-infrared radiation using coherently controlled directional photocurrent in semiconductors

Jacob B. Khurgin

Appl. Phys. Lett. 74, 4 (1999); http://dx.doi.org/10.1063/1.123115 (3 pages) | Cited 9 times

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We propose a method of heterodyne detection of far-infrared signals using generation of directional current in semiconductors via a coherent interaction of one- and two-photon absorption, and evaluate the sensitivity and detectivity of this method. © 1999 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Pz Photoconduction and photovoltaic effects
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors

Laser action from two-dimensional distributed feedback in photonic crystals

M. Meier, A. Mekis, A. Dodabalapur, A. Timko, R. E. Slusher, J. D. Joannopoulos, and O. Nalamasu

Appl. Phys. Lett. 74, 7 (1999); http://dx.doi.org/10.1063/1.123116 (3 pages) | Cited 160 times

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We report an analysis of the operation of a new type of laser resonator with two-dimensional distributed feedback from a photonic crystal. The gain medium consists of a 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole host doped with Coumarin 490 and DCM and is deposited on lithographically patterned Si/SiO2 structures. Bragg reflections caused by the grating diminish the group velocity of photons along some directions of crystallographic symmetry to zero, and the resulting feedback gives rise to laser oscillations. Dispersion relations for photons were calculated analytically and are used to interpret the laser emission spectra. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Permanent photoreduction of Sm3+ to Sm2+ inside a sodium aluminoborate glass by an infrared femtosecond pulsed laser

Jianrong Qiu, K. Miura, T. Suzuki, T. Mitsuyu, and K. Hirao

Appl. Phys. Lett. 74, 10 (1999); http://dx.doi.org/10.1063/1.123117 (3 pages) | Cited 47 times

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We report the observation of permanent photoreduction of Sm3+ to Sm2+ inside a transparent and colorless Sm3+-doped sodium aluminoborate glass. After irradiation by an 800 nm focused femtosecond pulsed laser, the focused part of the laser in the glass became orange. Absorption and photoluminescence spectra showed that a part of Sm3+ was reduced to Sm2+ after the laser irradiation. Electron spin resonance spectra of the glass before and after the laser irradiation were also measured. The observed phenomenon is inferred to be useful for the fabrication of optical memory devices with an ultrahigh storage density. © 1999 American Institute of Physics.
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82.50.-m Photochemistry
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.55.Hx Other solid inorganic materials
76.30.Kg Rare-earth ions and impurities
42.70.Ce Glasses, quartz

Low loss photoinduced waveguides in rapid thermally annealed films of chalcogenide glasses

S. Ramachandran and S. G. Bishop

Appl. Phys. Lett. 74, 13 (1999); http://dx.doi.org/10.1063/1.123118 (3 pages) | Cited 27 times

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Rapid thermal annealing of sputter-deposited chalcogenide glasses is demonstrated to yield superior quality films which are used to fabricate low loss (<0.3 dB/cm) photoinduced channel waveguides in chalcogenide glasses. This process also enhances the photosensitivity and the magnitude of photoinduced index changes possible (Δn ∼ 5%) in these glass systems. © 1999 American Institute of Physics.
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42.70.Ce Glasses, quartz
42.70.Gi Light-sensitive materials
42.82.Et Waveguides, couplers, and arrays
78.66.Jg Amorphous semiconductors; glasses
61.43.Fs Glasses
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of optical interference on quantum well infrared photodetectors in a 45° waveguide geometry

H. Schneider, C. Schönbein, M. Walther, P. Koidl, and G. Weimann

Appl. Phys. Lett. 74, 16 (1999); http://dx.doi.org/10.1063/1.123119 (3 pages) | Cited 19 times

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Standing light waves caused by the interference of incident and reflected beams lead to a spatial modulation of the electromagnetic field within the active region of a quantum well infrared photodetector (QWIP). The optical excitation—determined by the electric field component perpendicular to the quantum well plane—is thus inhomogeneous, influencing the QWIP responsivity and its voltage dependence. The inhomogeneity can be suppressed by using mesa photodetectors where only half of the top contact is covered with metal. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Photoinduced birefringence and reversible optical storage in liquid-crystalline azobenzene side-chain polymers

Changshun Wang, Haosheng Fei, Yong Qiu, Yanqiang Yang, Zhenqian Wei, Yanqing Tian, Yongmei Chen, and Yingying Zhao

Appl. Phys. Lett. 74, 19 (1999); http://dx.doi.org/10.1063/1.123138 (3 pages) | Cited 26 times

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A liquid crystal with an azobenzene moiety as a photoactive mesogenic unit is investigated in photoinduced birefringence. Measurements reveal that it possesses large magnitude of photoinduced birefringence (Δn ∼ 10−2) and the characteristic of long-term optical storage. The resulting polarization information can be erased either by heating the sample to a temperature much higher than the glass transition temperature, or by optical method with a circularly polarized light. The mechanism of long-term optical storage is discussed in this letter. © 1999 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
78.20.Fm Birefringence
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

An x-ray spectromicroscopic study of electromigration in patterned Al(Cu) lines

H. H. Solak, G. F. Lorusso, S. Singh-Gasson, and F. Cerrina

Appl. Phys. Lett. 74, 22 (1999); http://dx.doi.org/10.1063/1.123120 (3 pages) | Cited 12 times

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We studied the surface properties of patterned Al(Cu) lines related to the electromigration phenomena using photoemission spectromicroscopy techniques. We stressed the lines for electromigration in situ in the ultrahigh vacuum microscope chamber and observed the changes on the line surface. Our results show surface precipitation of Cu beneath the Al2O3 layer on the line surface as well as on side walls. Enrichment of grain boundaries in Cu due to electromigration flux was observed in areas downstream of voids with respect to the electron flow. © 1999 American Institute of Physics.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Pattern formation and shadow instability in collimated energetic molecular beam growth of silicon

S. E. Roadman, S. W. Levine, Y.-J. Zheng, P. Clancy, and J. R. Engstrom

Appl. Phys. Lett. 74, 25 (1999); http://dx.doi.org/10.1063/1.123121 (3 pages) | Cited 1 time

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Epitaxial silicon thin films were deposited on Si(100) substrates at variable angles of incidence using well-collimated supersonic molecular beams of disilane, Si2H6. The resulting thin-film surface topology has been examined using atomic force microscopy. Rough surface morphology is observed as the beam angle of incidence is increased above ∼60°. Thin films deposited at substrate temperatures ⩽600 °C exhibit anisotropic features, which are elongated in a direction perpendicular to the incident beam. Increasing the substrate temperature leads to films with increased root-mean-square roughness and larger characteristic features, maintaining a nearly constant feature aspect ratio. Analysis indicates that the film feature size is controlled by a competition between roughening driven by the shadow instability and smoothening driven by surface mass transport. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation

Surface conditioning of chemical vapor deposited hexagonal boron nitride film for negative electron affinity

Kian Ping Loh, Isao Sakaguchi, Mikka Nishitani Gamo, Shigeru Tagawa, Takashi Sugino, and Toshihiro Ando

Appl. Phys. Lett. 74, 28 (1999); http://dx.doi.org/10.1063/1.123122 (3 pages) | Cited 45 times

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The surface conditions favoring a negative electron affinity (NEA) on hexagonal boron nitride (h-BN) grown by radio-frequency plasma-assisted chemical vapor deposition (CVD) have been investigated by ultraviolet photoelectron spectroscopy. The NEA condition on the h-BN film appears to be resistant to oxygen-plasma or in-vacuo atomic oxygen treatment. It is not certain whether the segregation of bulk hydrogen onto the surface helps to promote the NEA; the depth profile of the deposited film reveals about 0.01%–0.1% atomic concentration of hydrogen. High temperature annealing at 1100 °C results in a positive electron affinity surface (PEA). Reexposure of PEA surface to atomic hydrogen at room temperature regenerates the NEA condition. This is evident of the role of superficial hydrogen in promoting NEA on the h-BN film. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.65.-b Surface treatments
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing

Activation volume for boron diffusion in silicon and implications for strained films

Yuechao Zhao, Michael J. Aziz, Hans-J. Gossmann, Salman Mitha, and David Schiferl

Appl. Phys. Lett. 74, 31 (1999); http://dx.doi.org/10.1063/1.123123 (3 pages) | Cited 22 times

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The diffusivity of B in Si is enhanced by pressure, characterized by an activation volume of V∗ = −0.17±0.01 times the atomic volume; V∗ is close to the formation volume of the self-interstitial determined by atomistic calculations. The results for hydrostatic pressure are used to make predictions for the effect of biaxial strain on diffusion. Assuming an interstitial-based mechanism and a range of values for the anisotropy in the migration volume, comparison is made between our results, the atomistic calculations, and the measured dependence of B diffusion on biaxial strain. We find a qualitative consistency for an interstitial-based mechanism with the measured strain effect on diffusion in Si–Ge alloys, but not with the measured strain effect in pure Si. Experiments and calculations to determine the origin of this discrepancy are discussed. © 1999 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.J- Point defects and defect clusters
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Defect generation and diffusion mechanisms in Al and Al–Cu

C.-L. Liu, X.-Y. Liu, and L. J. Borucki

Appl. Phys. Lett. 74, 34 (1999); http://dx.doi.org/10.1063/1.123124 (3 pages) | Cited 17 times

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A defect generation mechanism, namely, the grain-boundary Frenkel pair model, and corresponding diffusion mechanisms during electromigration are developed using atomic simulation techniques in Al and Al–Cu. We contend that large numbers of interstitials and vacancies exist at grain boundaries and both contribute to mass transport. Cu preferentially segregates to the interstitial sites at grain boundaries via a Frenkel pair generation process and reduces the overall grain-boundary diffusivity due to the stronger Al–Cu binding. Predictions from our models are in excellent agreement with available experimental data and observations. © 1999 American Institute of Physics.
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66.30.Qa Electromigration
61.72.J- Point defects and defect clusters
61.72.Mm Grain and twin boundaries
66.30.Lw Diffusion of other defects

Diffusion and electromigration of copper in SiO2-passivated single-crystal aluminum interconnects

V. T. Srikar and C. V. Thompson

Appl. Phys. Lett. 74, 37 (1999); http://dx.doi.org/10.1063/1.123125 (3 pages) | Cited 11 times

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We have experimentally studied the diffusion and electromigration of Cu in passivated single-crystal Al interconnects, fabricated on oxidized Si wafers. The test structure consisted of parallel lines (0.4 μm thick and 5 μm wide), with alternating lines terminating in shared contact pads. Cu was locally added to the same regions in all the lines, and the effects of temperature and electric fields on diffusion along the lines were characterized by analyzing the Cu concentration profile measured by electron-probe microanalysis. The activation energy for diffusion was found to be 0.8±0.2 eV in the temperature range 320–400 °C, which suggests that the path for diffusion of Cu is along the Al/AlOx/SiOy interface for these single crystals. The apparent effective valence (Z∗) characterizing electromigration was measured to be −5.4±1.2 at 350 °C. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Fq Self-diffusion in metals, semimetals, and alloys
68.35.Fx Diffusion; interface formation
66.30.Qa Electromigration
81.65.Rv Passivation

Implications of a model for instability during film growth for strained InGaAs and SiGe layers

François Léonard and Rashmi C. Desai

Appl. Phys. Lett. 74, 40 (1999); http://dx.doi.org/10.1063/1.123126 (3 pages) | Cited 15 times

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We analyze experiments on the morphology of strained InGaAs and SiGe layers using a nonequilibrium stability analysis. Stability diagrams for growing films as a function of the deposition rate, the temperature and the misfit are calculated and compared to experimental reports. We show that for InGaAs layers, the onset of surface roughening is due to an instability against simultaneous modulations of the surface profile and the composition. For SiGe, the onset of surface roughening cannot be described by an instability, but rather, is due to a nucleation mechanism. © 1999 American Institute of Physics.
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81.15.Aa Theory and models of film growth
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.Dv Composition, segregation; defects and impurities

Ion channeling and x-ray diffraction study of tensely strained GaInP layers on InP

G. M. Cohen, D. Ritter, V. Richter, and R. Kalish

Appl. Phys. Lett. 74, 43 (1999); http://dx.doi.org/10.1063/1.123127 (3 pages) | Cited 5 times

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Layers of Ga0.25In0.75P were grown on InP by metalorganic molecular beam epitaxy and studied by ion channeling and asymmetric high-resolution x-ray diffraction. The angular difference between the substrate and the layer channeling angles agreed with the corresponding angular difference calculated from the x-ray results. Negligible relaxation was found in Ga0.25In0.75P layers up to a thickness of 50 nm. Thicker layers were found to be partially relaxed. In the channeling experiments an additional minimum in the substrate angular scan profile at an angle corresponding roughly to the layer’s minimum yield was found. This extra minimum was attributed to the steering effect at the strained GaInP/InP interface [S. Hashimoto, Y. Q. Feng, W M. Gibson, L. J. Schowalter, and B. D. Hunt, Nucl. Instrum. Methods B 13, 45 (1986)], and was confirmed by a comparison with the x-ray diffraction measurements. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.05.Ea III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Nanofaceting of the LiNbO3 surface studied by scanning tunneling microscopy

D. L. Carroll, T. Wagner, and M. Rühle

Appl. Phys. Lett. 74, 46 (1999); http://dx.doi.org/10.1063/1.123128 (3 pages)

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The surfaces of LiNbO3 single crystals have been studied using scanning tunneling microscopy and tunneling spectroscopy. Vacuum reduction was used to provide sufficient conductivity for tunneling. After reduction, the surfaces are dominated by nanoscale. Auger shows the structures to be related to precipitated suboxides of LiNbO3 which can be correlated to asymmetries in Li diffusion within the bulk crystal. These surface nanophases have electronic properties which are strongly dependent on the frequency of applied electric fields. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
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
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
79.20.Fv Electron impact: Auger emission
64.75.-g Phase equilibria
66.30.H- Self-diffusion and ionic conduction in nonmetals

Self- and interdiffusion in AlXGa1−XAs/GaAs isotope heterostructures

H. Bracht, E. E. Haller, K. Eberl, and M. Cardona

Appl. Phys. Lett. 74, 49 (1999); http://dx.doi.org/10.1063/1.123129 (3 pages) | Cited 17 times

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We report self- and interdiffusion studies between 800 and 1160 °C in buried Al71GaAs/Al69GaAs/71GaAs and AlAs/71GaAs isotope heterostructures. Ga diffusion at Al71GaAs–Al69GaAs interfaces was found to decrease with increasing Al content. Al–Ga interdiffusion at AlGaAs–GaAs and AlAs–GaAs interfaces reveals a concentration dependent interdiffusion coefficient. The temperature dependence of Ga and Al diffusion in GaAs and of Ga diffusion in AlGaAs is described by a single activation enthalpy in the range of 3.6±0.1 eV, but with different pre-exponential factors. The experimentally observed higher Al diffusion in GaAs compared to Ga self-diffusion as well as the decreasing Ga diffusion with increasing Al content is explained. © 1999 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
66.30.H- Self-diffusion and ionic conduction in nonmetals
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Formation of aluminum oxynitride diffusion barriers for Ag metallization

Y. Wang and T. L. Alford

Appl. Phys. Lett. 74, 52 (1999); http://dx.doi.org/10.1063/1.123130 (3 pages) | Cited 26 times

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Aluminum oxynitride (AlxOyNz) diffusion barriers have been formed in the temperature range of 400–725 °C by annealing Ag/Al bilayers on oxidized Si substrates in an ammonia (NH3) ambient. Rutherford backscattering spectrometry showed that the out-diffused Al reacted with ammonia and oxygen in the ambient and encapsulated the Ag films. The resulting Ag resistivity values are 1.75±0.35 μΩ cm. Higher processing temperatures and thinner original Al layers showed to improve the resistivity of the encapsulated Ag layers. The thermal stability of these diffusion barriers was evaluated by depositing 50 nm of Cu films onto the encapsulated samples, and then annealing in either vacuum or flowing He-0.5%H2. Results showed that these barriers sustained interdiffusion between Cu and Ag up to 620 °C at least for 30 min in either ambient. This temperature is a 200 °C improvement over previously reported values for the self-encapsulated Cu and Ag films. © 1999 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Ns Metal-nonmetal contacts
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
61.72.Cc Kinetics of defect formation and annealing

Simulation of hyperthermal deposition of Si and C on SiC surfaces

Dominic R. Alfonso and Sergio E. Ulloa

Appl. Phys. Lett. 74, 55 (1999); http://dx.doi.org/10.1063/1.123131 (3 pages) | Cited 3 times

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We describe the adsorption dynamics of Si and C atoms at supersonic velocities on Si- and C-terminated 6H–SiC(0001) substrates using molecular dynamics simulations. The sticking probabilities of adatoms are found to be very high and not to change substantially with increasing incident kinetic energy. We identify two mechanisms responsible for the high sticking probabilities of the adatoms: (a) efficient transfer of adatom energy to the substrate and (b) strong attractive forces experienced by the impinging adatom over the entire surface. The calculated potential energy surfaces reveal possible binding sites of the adatoms on the substrates. © 1999 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
82.20.Wt Computational modeling; simulation
82.20.Kh Potential energy surfaces for chemical reactions

Real-time measurement of the evolution of carrier mobility in thin-film semiconductors during growth

R. Brenot, R. Vanderhaghen, B. Drévillon, and P. Roca i Cabarrocas

Appl. Phys. Lett. 74, 58 (1999); http://dx.doi.org/10.1063/1.123132 (3 pages) | Cited 7 times

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A method which allows real-time microwave mobility measurements in thin-film semiconductors is described. Carriers mobility is determined during growth by combining two diagnostics: time-resolved microwave conductivity (TRMC) and spectroscopic ellipsometry (SE). TRMC provides the product of the number of free carriers, generated by a laser pulse, by their microwave mobility. The number of photogenerated carriers is calculated from real-time SE measurements. Therefore, the mobility of excess carriers in the growing layer can be deduced from TRMC measurements. In order to illustrate this technique, a TRMC setup has been implemented in situ together with real-time SE to analyze the growth of microcrystalline silicon (μc-Si) by radio frequency glow discharge. An increase of the average carrier mobility as a function of the film thickness is observed, which is compared with the increase of the crystalline fraction evidenced by SE. © 1999 American Institute of Physics.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Mx High-frequency effects; plasma effects
07.60.Fs Polarimeters and ellipsometers
72.80.Cw Elemental semiconductors

Femtosecond near-field optical spectroscopy of implantation patterned semiconductors

B. A. Nechay, U. Siegner, F. Morier-Genoud, A. Schertel, and U. Keller

Appl. Phys. Lett. 74, 61 (1999); http://dx.doi.org/10.1063/1.123133 (3 pages) | Cited 25 times

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We have developed a femtosecond-resolved near-field scanning optical microscope, using a diffraction-limited pump and near-field probe configuration, which allows us to measure carrier dynamics with a spatial resolution of ∼150 nm and a time resolution of ∼250 fs. This instrument is used for near-field degenerate pump–probe studies of carrier dynamics in GaAs/AlGaAs single quantum well samples locally patterned by focused-ion-beam (FIB) implantation. We find that lateral carrier diffusion across the nanometer-scale FIB pattern plays a significant role in the decay of the excited carriers. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Epitaxial MnAs/GaAs/MnAs trilayer magnetic heterostructures

M. Tanaka, K. Saito, and T. Nishinaga

Appl. Phys. Lett. 74, 64 (1999); http://dx.doi.org/10.1063/1.122953 (3 pages) | Cited 41 times

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We have successfully grown MnAs/GaAs/MnAs ferromagnet/semiconductor trilayer heterostructures on GaAs(111)B substrates by molecular beam epitaxy. The epitaxial orientations of MnAs and GaAs are (0001) and (111), respectively, as expected. It was found that epitaxial monocrystalline GaAs can be grown on the As-rich (3×2)-(0001) MnAs surface. Cross-sectional images by transmission electron microscopy showed that the trilayers are formed as intended with fairly smooth and atomically abrupt interfaces. Double-step features were observed in magnetization characteristics due to the difference in coercive force between the top and bottom MnAs layers. The interlayer coupling was small when the thickness of the GaAs spacer layer was 5–10 nm. © 1999 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Ey III-V semiconductors
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Improved hydrogenated amorphous silicon thin films by photon assisted microwave electron cyclotron resonance chemical vapor deposition

Y. J. Song and W. A. Anderson

Appl. Phys. Lett. 74, 67 (1999); http://dx.doi.org/10.1063/1.122954 (3 pages) | Cited 1 time

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The conventional microwave electron cyclotron resonance chemical vapor deposition process has been modified by illuminating the substrate with a tungsten halogen lamp beam of intensity 0.1–1 W/cm2 during the deposition of hydrogenated amorphous silicon films. Compared to the conventional process without photon assist, this technique provides improved photoconductivity, carrier lifetime, and solar cell efficiency, as well as reduced light-induced degradation. The efficiency of undoped hydrogenated amorphous silicon/p-type crystalline silicon solar cells fabricated by this process is 10%, without an antireflective coating, and has degraded to only 9.8% after 3 weeks continuous exposure to light. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.05.Gc Amorphous semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
84.60.Jt Photoelectric conversion
72.80.Cw Elemental semiconductors
72.80.Ng Disordered solids
73.61.Jc Amorphous semiconductors; glasses
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects

Low-resistance Pt/Ni/Au ohmic contacts to p-type GaN

Ja-Soon Jang, In-Sik Chang, Han-Ki Kim, Tae-Yeon Seong, Seonghoon Lee, and Seong-Ju Park

Appl. Phys. Lett. 74, 70 (1999); http://dx.doi.org/10.1063/1.123954 (3 pages) | Cited 80 times

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We report on a Pt (20 nm) Ni (30 nm)/Au (80 nm) metallization scheme for low-resistance ohmic contacts to the moderately doped p-type GaN:Mg (3×1017 cm−3). Both as-deposited and annealed Pt/Ni/Au contacts on p-GaN exhibit linear current–voltage characteristics, showing that a high-quality ohmic contact is formed. The Pt/Ni/Au scheme shows the specific contact resistance of 5.1×10−4 Ω cm2 when annealed at 350 °C for 1 min in a flowing N2 atmosphere. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential
85.40.Ls Metallization, contacts, interconnects; device isolation
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Enhanced critical currents in melt textured YBa2Cu3O7 by cold isostatic pressing

B. Martínez, F. Sandiumenge, T. Puig, X. Obradors, L. Richard, and J. Rabier

Appl. Phys. Lett. 74, 73 (1999); http://dx.doi.org/10.1063/1.122955 (3 pages) | Cited 10 times

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An enhancement of the critical currents in the H‖c configuration, reaching 100% at 77 K, has been obtained in melt textured YBa2Cu3O7/Y2BaCuO5 composites after a cold isostatic pressing process (300 °C, PAr = 200 MPa). A transmission electron microscopy analysis of the microstructure demonstrates that a high density of nanometric stacking fault loops, with anisotropic growth within the (001) plane, is generated. The improvement of critical currents is attributed to the flux pinning enhancement due to the increased length of the 1/6〈031〉 partial dislocations surrounding nanometric stacking faults. We stress that this technique has high potential for the large scale processing of high critical currents superconducting ceramic composites. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
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