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17 Sep 2001

Volume 79, Issue 12, pp. 1745-1922

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Continuous-wave operation of a 5.2 μm quantum-cascade laser up to 210 K

Brian Ishaug, Wen-Yen Hwang, Jae Um, Bujin Guo, Hao Lee, and Chih-Hsiang Lin

Appl. Phys. Lett. 79, 1745 (2001); http://dx.doi.org/10.1063/1.1402644 (3 pages) | Cited 13 times

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Continuous-wave operation of a 5.2 μm-type I quantum-cascade laser with more than 5 mW of output power is reported at a heat sink temperature of 210 K (−63 °C). This temperature is within the range obtainable with thermal-electric coolers. The device was mounted epi-side down on a copper submount and exhibited a thermal resistance of ∼10 K/W at 210 K. Using the experimentally determined values for T0 = 136 K, J0 = 535 A/cm2 and Vop = 8.1 V and the above thermal resistance, the maximum theoretical operating temperature was found to be 212 K, in close agreement with experiment. Thermal simulations show that by improving the device design and heat sinking, thermal resistance can be reduced to 8.8 K/W and the maximum cw operating temperature can be increased to 230 K. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
81.05.Ea III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells

Three-photon phenomena in the upconversion luminescence of erbium–ytterbium-codoped phosphate glass

Feng Song, Guangyin Zhang, Meiru Shang, Hao Tan, Jia Yang, and Fanzhen Meng

Appl. Phys. Lett. 79, 1748 (2001); http://dx.doi.org/10.1063/1.1404996 (3 pages) | Cited 38 times

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Frequency upconversion into green and red luminescence in erbium–ytterbium-codoped phosphate glass pumped with a 970 nm diode laser is presented. The red upconversion emission results from a two-photon excitation process. The green emission results from a two- or three-photon excitation process with the two-photon process dominating at low pumping power. Based on measurement of the excitation and emission spectra, a model of the three-photon excitation process has been developed. This model provides a good basis for explaining the effect of the three-photon process on the saturation of 1.54 μm laser power of Er, Yb-codoped phosphate glass laser. © 2001 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
78.66.Jg Amorphous semiconductors; glasses

Laser frequency converter for continuous-wave tunable Ti:sapphire lasers based on aperiodically poled LiNbO3:Nd3+

J. Capmany, J. A. Pereda, V. Bermúdez, D. Callejo, and E. Diéguez

Appl. Phys. Lett. 79, 1751 (2001); http://dx.doi.org/10.1063/1.1404123 (3 pages) | Cited 7 times

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We present a laser device that shifts the frequencies contained in the 750–850 nm emission band interval of a continuous wave Ti:sapphire tunable laser and produces continuous-wave tunable laser radiation between 440 and 475 and 485 and 505 nm. The device is based on self-sum-frequency mixing of the tunable emission of a Ti:sapphire laser injected in the cavity of a diode-pumped aperiodically poled Nd3+:LiNbO3 laser oscillating in continuous-wave at 1084 or 1372 nm. © 2001 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
42.60.Fc Modulation, tuning, and mode locking
77.22.Ej Polarization and depolarization
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Orientation-controlled epitaxy of A2CuO3 (A: Sr, Ca) films with large optical nonlinearity

T. Manako, Y. Okimoto, M. Izumi, S. Shinomori, M. Kawasaki, H. Kishida, H. Okamoto, T. Fukumura, M. Ohtani, and Y. Tokura

Appl. Phys. Lett. 79, 1754 (2001); http://dx.doi.org/10.1063/1.1402161 (3 pages) | Cited 5 times

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The one-dimensional Cu–O chains responsible for the large optical nonlinearity in Sr2CuO3 (SCO) and Ca2CuO3 (CCO) are aligned in one direction in films grown on LaSrAlO4 (LSAO) (1 0 0) substrates by using pulsed laser deposition. The CCO films deposited directly on lattice matched LSAO substrates have a single orientation with high crystallinity, while the SCO films include small portions of misoriented domains. Using a simple model of lattice mismatch, we developed a Sr2TiO4 buffer layer in order to grow orientation-controlled SCO films with both high crystallinity and a sharp optical absorption edge. This technique will be a key to fabricating ultrafast all-optical switches with a waveguide structure. © 2001 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
42.79.Wc Optical coatings
78.66.Nk Insulators
42.65.-k Nonlinear optics
42.70.Mp Nonlinear optical crystals
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Formation and decay of nonbridging oxygen hole centers in SiO2 glasses induced by F2 laser irradiation: In situ observation using a pump and probe technique

Koichi Kajihara, Linards Skuja, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 79, 1757 (2001); http://dx.doi.org/10.1063/1.1404407 (3 pages) | Cited 31 times

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Formation and decay of nonbridging oxygen hole centers (NBOHC, an oxygen dangling bond) in SiO2 glasses by F2 excimer laser (7.9 eV) irradiation were in situ analyzed by monitoring 1.9 eV photoluminescence of NBOHC using a pump and probe technique. In wet SiO2, the SiO–H bond was efficiently photolyzed by F2 laser photons to form NBOHC with a quantum yield of ∼ 0.2. However, the recombination with dissociated hydrogenous species suppressed the buildup of NBOHC. In dry SiO2, in contrast, NBOHC formation by dissociation of strained Si–O–Si bonds was inefficient but NBOHC accumulated with the number of F2 pulses due to a negligibly slow reverse recombination reaction. © 2001 American Institute of Physics.
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71.55.Jv Disordered structures; amorphous and glassy solids
78.55.Hx Other solid inorganic materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators

Vertical and lateral heterogeneous integration

Jon Geske, Yae L. Okuno, John E. Bowers, and Vijay Jayaraman

Appl. Phys. Lett. 79, 1760 (2001); http://dx.doi.org/10.1063/1.1404399 (3 pages) | Cited 13 times

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A technique for achieving large-scale monolithic integration of lattice-mismatched materials in the vertical direction and the lateral integration of dissimilar lattice-matched structures has been developed. The technique uses a single nonplanar direct-wafer-bond step to transform vertically integrated epitaxial structures into lateral epitaxial variation across the surface of a wafer. Nonplanar wafer bonding is demonstrated by integrating four different unstrained multi-quantum-well active regions lattice matched to InP on a GaAs wafer surface. Microscopy is used to verify the quality of the bonded interface, and photoluminescence is used to verify that the bonding process does not degrade the optical quality of the laterally integrated wells. The authors propose this technique as a means to achieve greater levels of wafer-scale integration in optical, electrical, and micromechanical devices. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
81.07.St Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells

Optical gain and saturation in nitride-based laser structures

M. Vehse, P. Michler, O. Lange, M. Röwe, J. Gutowski, S. Bader, H.-J. Lugauer, G. Brüderl, A. Weimar, A. Lell, and V. Härle

Appl. Phys. Lett. 79, 1763 (2001); http://dx.doi.org/10.1063/1.1401780 (3 pages) | Cited 7 times

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We have performed systematic studies of the optical gain and its saturation in (In, Ga)N/GaN/(Al, Ga)N laser structures that depend on the excitation density and number of quantum wells. The unsaturated gain factor which was obtained by the variable stripe-length method increases with excitation power, i.e., increasing modal gain. The gain factor also increases with a decreasing number of quantum wells, as is shown by the investigation of a series of laser structures with 3, 4, 5, and 10 quantum wells for fixed modal gain. Values up to 40 dB at 300 K were measured. Thermal activation energies obtained by temperature dependent photoluminescence measurements yield information on the influence of nonradiative recombination processes on optical gain saturation. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells

Continuous room-temperature operation of electrically pumped quantum-dot microcylinder lasers

M. Arzberger, G. Böhm, M.-C. Amann, and G. Abstreiter

Appl. Phys. Lett. 79, 1766 (2001); http://dx.doi.org/10.1063/1.1403656 (3 pages) | Cited 5 times

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We report continuous-wave (cw) room-temperature operation of electrically pumped AlGaAs/GaAs microcylinder lasers using self-assembled InAs/GaAs quantum dots (QDs) as the active material. The threshold currents are lower than those of similar devices with an InGaAs quantum well fabricated for comparison. This is discussed in terms of nonradiative surface recombination at the sidewall of the resonator which has less influence in the case of the QD devices since the lateral carrier confinement suppresses lateral carrier diffusion. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
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
73.21.La Quantum dots
42.60.By Design of specific laser systems
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Fd III-V semiconductors
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Comparison of negative-ion and positive-ion-assisted etching of silicon

Sivananda K. Kanakasabapathy, Marwan H. Khater, and Lawrence J. Overzet

Appl. Phys. Lett. 79, 1769 (2001); http://dx.doi.org/10.1063/1.1400765 (3 pages) | Cited 8 times

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Relatively electron-free, positive- and negative-ion (ion–ion) plasmas have been achieved in the afterglow of pulsed-power Cl2 discharges. The application of a pulsed dc bias phase locked to the source power modulation and exclusive to the ion–ion plasma, allows selective bombardment by positive (Cl2+) or negative (Cl−) ions onto a silicon substrate. This allows an equitable comparison of etching by equal energy ions of both polarities. We find that at 50 eV, Cl2+ etches twice as fast as Cl−. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.20.Pm Rate constants, reaction cross sections, and activation energies
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Variance method for the evaluation of particle size and dislocation density from x-ray Bragg peaks

A. Borbély and I. Groma

Appl. Phys. Lett. 79, 1772 (2001); http://dx.doi.org/10.1063/1.1404134 (3 pages) | Cited 27 times

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A method is presented to determine the particle size and internal strain from broadened x-ray peaks obtained on small coherent domains containing dislocations. In contrast with the evaluation techniques applied earlier, the proposed procedure requires only the measurement of a single line profile. It is based on the asymptotic behavior of the second-and fourth-order restricted moments. At the asymptotic part of the second-order restricted moment, the finite grain size causes a linear diffraction vector dependence, while that of the dislocation-induced strain is logarithmic. On the fourth-order moment, the two sources of broadening result in cubic and parabolic behavior. The method is illustrated by analyzing x-ray peaks measured on a cold-and hot-deformed AlMg alloy and on a nanocrystalline iron powder. © 2001 American Institute of Physics.
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61.05.cp X-ray diffraction
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.07.Bc Nanocrystalline materials

Electronic structure of noncrystalline transition metal silicate and aluminate alloys

G. Lucovsky, G. B. Rayner, D. Kang, G. Appel, R. S. Johnson, Y. Zhang, D. E. Sayers, H. Ade, and J. L. Whitten

Appl. Phys. Lett. 79, 1775 (2001); http://dx.doi.org/10.1063/1.1404997 (3 pages) | Cited 36 times

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A localized molecular orbital description (LMO) for the electronic states of transition metal (TM) noncrystalline silicate and aluminate alloys establishes that the lowest conduction band states are derived from d states of TM atoms. The relative energies of these states are in agreement with the LMO approach, and have been measured by x-ray absorption spectroscopy for ZrO2–SiO2 alloys, and deduced from an interpretation of capacitance–voltage and current–voltage data for capacitors with Al2O3–Ta2O5 alloy dielectrics. The LMO model yields a scaling relationship for band offset energies providing a guideline for selection of gate dielectrics for advanced Si devices. © 2001 American Institute of Physics.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
78.70.Dm X-ray absorption spectra

Radial-pattern formation in the polycarbonate substratum of recordable compact disks

M. Tanimura, I. Ishikawa, M. Tachibana, K. Shinozaki, and K. Kojima

Appl. Phys. Lett. 79, 1778 (2001); http://dx.doi.org/10.1063/1.1400778 (3 pages) | Cited 2 times

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A radial pattern is found to form in the polycarbonate (PC) substratum of a recordable compact disk. Characteristic features of the pattern are that it is composed of about 80 needle-like regions, the shape of which closely resembles a thin film. In addition, white light is found to scatter at the needle-like region/matrix boundaries. This suggests that the PC substratum may have inferior transparency due to the formation of this pattern. Thus, it is important to understand the bifurcation of the radial-pattern formation from the viewpoint of materials science and engineering. Based on the mechanics of the PC viscous fluid, it has been found that the bifurcation of the pattern formation has a Reynolds number of about 10−3. © 2001 American Institute of Physics.
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42.70.Jk Polymers and organics
42.79.Vb Optical storage systems, optical disks
61.41.+e Polymers, elastomers, and plastics

Antiphase-boundary extension in single-variant CuPt–B ordered Ga0.47In0.53As on InP

S. P. Ahrenkiel and M. C. Hanna

Appl. Phys. Lett. 79, 1781 (2001); http://dx.doi.org/10.1063/1.1403255 (2 pages) | Cited 1 time

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We describe the extension (tilt) of antiphase boundaries (APBs) in single-variant, CuPt–B ordered, epitaxial Ga0.47In0.53As films grown by low-pressure metalorganic chemical vapor deposition on (001) InP miscut 6° toward (111)B. The mean extension angles [measured from (001) toward the (111)B ordering plane] range from approximately 90° to 123° in these samples. We suggest that APBs propagate in step-flow growth mode as advancing step edges traverse the intersections of extant APBs and the vicinal (001) surface. © 2001 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Atomic-scale surface control and second-harmonic generation in GdxY1−xCa4O(BO3)3 thin films grown by combinatorial laser molecular-beam epitaxy

T.-W. Kim, N. Arai, H. Koinuma, Y. Matsumoto, M. Yoshimura, H. Furuya, H. Nakao, Y. Mori, and T. Sasaki

Appl. Phys. Lett. 79, 1783 (2001); http://dx.doi.org/10.1063/1.1402964 (3 pages)

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We studied the atomic-scale growth control and second-harmonic generation (SHG) properties of GdxY1−xCa4O(BO3)3 thin films. Combinatorial laser molecular-beam epitaxy was employed to optimize the growth conditions of the film. Ultrasmooth GdxY1−xCa4O(BO3)3 thin films with step-and-terrace structure were obtained by using atomically controlled GdCa4O(BO3)3 substrates. The dependence of SHG intensity on the fundamental wave polarization angle was studied for the epitaxial film on (010) GdCa4O(BO3)3 substrate in comparison for the randomly oriented film on (0001) sapphire substrate. It was found that only the epitaxially grown film clearly exhibited a fourfold SHG intensity showing type-II phase-matching direction. © 2001 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

A-site surface termination in strontium titanate single crystals

A. G. Schrott, J. A. Misewich, M. Copel, D. W. Abraham, and Y. Zhang

Appl. Phys. Lett. 79, 1786 (2001); http://dx.doi.org/10.1063/1.1404129 (3 pages) | Cited 13 times

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It is well known that chemical etching of strontium titanate (SrTiO3) results in titanium-terminated (B site) surfaces. In this letter, we describe a facile method for generating strontium-terminated surfaces in SrTiO3. We demonstrate that a substrate treatment consisting of a low-power oxygen ashing followed by annealing yields a strontium (A site)-terminated surface in single-crystal SrTiO3 (100). This surface termination of the substrate allows the deposition of cuprate films with improved quality. © 2001 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)

Cathodoluminescence study of diluted magnetic semiconductor quantum well/micromagnet hybrid structures

J. Kossut, I. Yamakawa, A. Nakamura, G. Cywiński, K. Fronc, M. Czeczott, J. Wróbel, F. Kyrychenko, T. Wojtowicz, and S. Takeyama

Appl. Phys. Lett. 79, 1789 (2001); http://dx.doi.org/10.1063/1.1405150 (3 pages) | Cited 30 times

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Cathodoluminescence (CL) was studied in hybrid structures consisting of a diluted magnetic semiconductor (DMS) Cd1−xMnxTe (x = 0.06 and 0.09) quantum well buried 300 Å below the surface on which Fe islands with micrometric dimensions were deposited. The CL at T = 10 K collected from areas far away from the Fe island was consistent with the photoluminescence spectra obtained prior to Fe deposition as were the raster scans and spot excited CL spectra taken in nonmagnetized structures close to the Fe islands. After a magnetization at a magnetic field of 3 T, the CL peak related to DMS quantum well (QW) shifts by up to 4 meV to lower energy only when the exciting beam is focused close to edges of an island. The observed shifts are interpreted as due to a fringe field, affecting the DMS QW, of magnetic domains formed in the Fe islands. The experiments prove a feasibility of the concept of usage of the fringe fields to achieve further confinement of excitons in submicron DMS/ferromagnet hybrid structures. © 2001 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
75.50.Pp Magnetic semiconductors
78.67.De Quantum wells
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Investigation of short-range order in nanocrystal-forming Zr60Cu20Pd10Al10 metallic glass and the mechanism of nanocrystal formation

Cang Fan, Muneyuki Imafuku, Hiroshi Kurokawa, Akihisa Inoue, and Volker Haas

Appl. Phys. Lett. 79, 1792 (2001); http://dx.doi.org/10.1063/1.1404128 (3 pages) | Cited 14 times

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Rapidly solidified ribbons from the nanocrystal-forming Zr60Cu20Pd10Al10 alloy prepared at various melting liquid temperatures were used to study the influence of the liquid state upon quenched-in nuclei. With lowering quenching liquid temperatures, the small-angle x-ray scattering shows increased related periodic composition fluctuations and the radial distribution function analysis from x-ray diffraction method reveals that the coordination number of Pd around Zr increases. These results provide evidence for the stronger attractive interaction in Zr–Pd, which exhibits large negative mixing enthalpy, leads to the formation of (Zr, Pd)-rich domains of short-range order in the liquid. They remain in the amorphous phase as quenched-in nuclei and therefore contribute to nanocrystalline formation. © 2001 American Institute of Physics.
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61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
81.05.Kf Glasses (including metallic glasses)
81.30.Fb Solidification
64.70.D- Solid-liquid transitions

Structural effects of the thermal treatment on a GaInNAs/GaAs superlattice

L. Largeau, C. Bondoux, G. Patriarche, C. Asplund, A. Fujioka, F. Salomonsson, and M. Hammar

Appl. Phys. Lett. 79, 1795 (2001); http://dx.doi.org/10.1063/1.1405002 (3 pages) | Cited 21 times

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We have studied structural changes that occur during annealing of GaInNAs/GaAs multiple quantum wells grown by metalorganic vapor-phase epitaxy (MOVPE). Different thermal treatments led to an improved room-temperature photoluminescence (PL) intensity, but also to room-temperature PL peak splitting. This splitting is related to the appearance of compositional clustering as displayed by transmission electron microscopy (TEM). In addition to this, interfacial layers on each side of the wells have also been observed by TEM and their composition is discussed on the basis of high resolution x-ray diffraction studies. It is suggested that the interface layers are indium deficient, but enriched in nitrogen, degrading the optical quantum well performance and indicating a need for improved switching sequences in the MOVPE growth. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Cd Superlattices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Fabrication of strained Si on an ultrathin SiGe-on-insulator virtual substrate with a high-Ge fraction

T. Tezuka, N. Sugiyama, and S. Takagi

Appl. Phys. Lett. 79, 1798 (2001); http://dx.doi.org/10.1063/1.1404409 (3 pages) | Cited 109 times

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A promising fabrication method for a Si1−xGex-on-insulator (SGOI) virtual substrate and evaluation of strain in the Si layer on this SGOI substrate are presented. A 9-nm-thick SGOI layer with x = 0.56 was formed by dry oxidation after epitaxial growth of Si0.92Ge0.08 on a silicon-on-insulator substrate. During the oxidation, Ge atoms were rejected from the surface oxide layer and condensed in the remaining SGOI layer, which was partially relaxed without introducing a significant amount of dislocations. It is found from the analysis of the Raman spectra that the strained Si layer grown on the SGOI layer involves a tensile strain of 1%. This strained Si on the SGOI structure is applicable to sub-100-nm metal–oxide–semiconductor field-effect transistors. © 2001 American Institute of Physics.
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81.05.Hd Other semiconductors
68.55.A- Nucleation and growth
81.65.Mq Oxidation
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors

Growth front roughening of room-temperature deposited oligomer films

D. Tsamouras, G. Palasantzas, and J. Th. M. De Hosson

Appl. Phys. Lett. 79, 1801 (2001); http://dx.doi.org/10.1063/1.1404132 (3 pages) | Cited 11 times

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Growth front scaling aspects are investigated by atomic force microscopy for oligomer 2,5-di-n-octyloxy-1,4-bis(4′-(styryl)styryl)-benzene thin films vapor deposited onto silicon substrates at room temperature. Analyses of the height–height correlation function for film thickness that are commonly used in optoelectronic devices, i.e., ranging between 15 and 300 nm, yield roughness Hurst exponents around H = 0.45±0.04. Further, the root-mean-square roughness amplitude σ evolves with film thickness as a power law σ∝dβ, with β = 0.28±0.05. The nonGaussian height distribution and the measured scaling exponents (H and β) suggest a roughening mechanism close to that described by the Kardar–Parisi–Zhang [Phys. Rev. Lett. 56, 889 (1986)] scenario indicating nonlinear film growth. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.70.Jk Polymers and organics
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Influence of Si growth temperature for embedding β-FeSi2 and resultant strain in β-FeSi2 on light emission from p-Si/β-FeSi2 particles/n-Si light-emitting diodes

T. Suemasu, Y. Negishi, K. Takakura, F. Hasegawa, and T. Chikyow

Appl. Phys. Lett. 79, 1804 (2001); http://dx.doi.org/10.1063/1.1405001 (3 pages) | Cited 30 times

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We have fabricated Si/β-FeSi2 particles/Si structures by reactive deposition epitaxy for β-FeSi2 and molecular-beam epitaxy (MBE) for Si. It was found that the photoluminescence (PL) intensity of β-FeSi2 strongly depended on MBE-Si growth temperature for embedding β-FeSi2 in Si. Room temperature 1.6 μm electroluminescence was realized from a Si-based light-emitting diode by embedding the β-FeSi2 active region with Si grown at 500 °C. Observation with transmission electron microscopy revealed that the a axis of β-FeSi2 from which PL was observed was about 9% longer than that of β-FeSi2 without PL or of bulk β-FeSi2. © 2001 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
81.15.Kk Vapor phase epitaxy; growth from vapor phase
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.61.Cw Elemental semiconductors
78.55.Ap Elemental semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Li Other semiconductors

Lattice constant variation and complex formation in zincblende gallium manganese arsenide

G. M. Schott, W. Faschinger, and L. W. Molenkamp

Appl. Phys. Lett. 79, 1807 (2001); http://dx.doi.org/10.1063/1.1403238 (3 pages) | Cited 54 times

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We perform high resolution x-ray diffraction on GaMnAs mixed crystals as well as on GaMnAs/GaAs and GaAs/MnAs superlattices for samples grown by low-temperature molecular-beam epitaxy under different growth conditions. Although all samples are of high crystalline quality and show narrow rocking curve widths and pronounced finite thickness fringes, the lattice constant variation with increasing manganese concentration depends strongly on the growth conditions: For samples grown at substrate temperatures of 220 and 270 °C, the extrapolated relaxed lattice constant of Zincblende MnAs is 0.590 nm and 0.598 nm, respectively. This is in contrast to low-temperature GaAs, for which the lattice constant decreases with increasing substrate temperature. © 2001 American Institute of Physics.
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61.66.Fn Inorganic compounds
75.50.Pp Magnetic semiconductors
68.65.Cd Superlattices
61.72.J- Point defects and defect clusters
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Thermal redistribution of localized excitons and its effect on the luminescence band in InGaN ternary alloys

Q. Li, S. J. Xu, W. C. Cheng, M. H. Xie, S. Y. Tong, C. M. Che, and H. Yang

Appl. Phys. Lett. 79, 1810 (2001); http://dx.doi.org/10.1063/1.1403655 (3 pages) | Cited 43 times

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Temperature-dependent photoluminescence measurements have been carried out in zinc-blende InGaN epilayers grown on GaAs substrates by metalorganic vapor-phase epitaxy. An anomalous temperature dependence of the peak position of the luminescence band was observed. Considering thermal activation and the transfer of excitons localized at different potential minima, we employed a model to explain the observed behavior. A good agreement between the theory and the experiment is achieved. At high temperatures, the model can be approximated to the band-tail-state emission model proposed by Eliseev et al. [Appl. Phys. Lett. 71, 569 (1997)]. © 2001 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Experimental comparison between optical spectroscopy and laser-ultrasound generation in polymer-matrix composites

Marc Dubois, Peter W. Lorraine, Robert J. Filkins, and Thomas E. Drake

Appl. Phys. Lett. 79, 1813 (2001); http://dx.doi.org/10.1063/1.1400776 (3 pages) | Cited 2 times

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Laser ultrasound is a technique based on lasers to generate and detect ultrasound. The generation mechanism involves several parameters among which one of the most important is the optical penetration depth. This letter presents a comparison between the amplitude of ultrasonic waves generated by an optical parametric oscillator and optical penetration depth spectra measured by photoacoustic spectroscopy in the 3.0 to 3.5 μm wavelength range for three different composite samples. The laser-ultrasound amplitude spectra closely track the photoacoustic spectra. The results presented in this letter experimentally demonstrate why the 3.0–3.5 μm wavelength range generates more efficiently generates ultrasonic waves in the ultrasonic frequency range of interest for the inspection of polymer-matrix composites than the 10.6 μm wavelength of the CO2 laser. © 2001 American Institute of Physics.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
81.05.Qk Reinforced polymers and polymer-based composites
62.65.+k Acoustical properties of solids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
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Ohmic contact formation mechanism of Ni on n-type 4H–SiC

Sang Youn Han, Ki Hong Kim, Jong Kyu Kim, Ho Won Jang, Kwang Ho Lee, Nam-Kyun Kim, Eun Dong Kim, and Jong-Lam Lee

Appl. Phys. Lett. 79, 1816 (2001); http://dx.doi.org/10.1063/1.1404998 (3 pages) | Cited 34 times

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Ohmic contact formation mechanism of Ni on n-type 4H–SiC is proposed by comparing the electrical properties with microstructural change. The ohmic behavior was observed at temperatures higher than 900 °C, but Ni2Si phase, as formerly reported to be responsible for ohmic contact, was formed after annealing at 600 °C. The higher work function of Ni2Si than Ni and the observation of graphite phase on the surface of Ni silicide after annealing at 950 °C support that a number of carbon vacancies were produced below the contact, playing a key role in forming an ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
61.72.Cc Kinetics of defect formation and annealing
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