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25 Mar 2002

Volume 80, Issue 12, pp. 2045-2227

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Highly efficient electrophosphorescent devices based on conjugated polymers doped with iridium complexes

Weiguo Zhu, Yueqi Mo, Min Yuan, Wei Yang, and Yong Cao

Appl. Phys. Lett. 80, 2045 (2002); http://dx.doi.org/10.1063/1.1461418 (3 pages) | Cited 72 times

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Iridium complexes with alkyl substituted 2-phenylpyridine, Ir(Bu-PPy)3, were synthesized. Polymer light emitting diodes with Ir complexes as the guest materials and the substituted polyphenylenes as the host were fabricated. Ir(Bu-PPy)3-doped Poly(2-(6-cyano-6-methyl)- heptyloxy-1,4-phenylene) (CNPPP) device showed generally higher quantum efficiency (QE) than that of Ir(PPy)3-doped device for a given dopant concentration. More importantly, the addition of butyl group into phenylpyridine ligand significantly suppresses the decay of device efficiency at high current density. For instance, for devices made with Ir(Bu-PPy)3-doped CNPPP: the maximum external quantum efficiency, QE, and luminance efficiency reached 5.1% ph/el and 12 cd/A, respectively, at 800 cd/m2 and maintained at 4.2% ph/el and 10 cd/A, respectively, at 2500 cd/m2. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
85.60.Pg Display systems
42.79.Kr Display devices, liquid-crystal devices
78.66.Qn Polymers; organic compounds

Improvement of λ ≈ 5 μm quantum cascade lasers by blocking barriers in the active regions

Q. K. Yang, C. Mann, F. Fuchs, R. Kiefer, K. Köhler, N. Rollbühler, H. Schneider, and J. Wagner

Appl. Phys. Lett. 80, 2048 (2002); http://dx.doi.org/10.1063/1.1462866 (3 pages) | Cited 11 times

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We report the improvement of quantum cascade lasers emitting at λ ∼ 5 μm by introducing AlAs blocking barriers together with strain-compensating InAs layers into the active regions. The blocking barriers are designed to selectively prevent electrons in the initial laser state from tunneling out of the active region, while maintaining the high tunneling probabilities of the electrons in the final laser states. Adopting blocking barriers, the maximum peak power per facet at 77 K (300 K) is increased from 285 (30 mW) to 900 mW (240 mW), and the maximum operation temperature in pulsed mode has been improved from 320 to 350 K with respect to a reference sample without blocking barriers. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.40.Gk Tunneling

Microgear laser

Masayuki Fujita and Toshihiko Baba

Appl. Phys. Lett. 80, 2051 (2002); http://dx.doi.org/10.1063/1.1462867 (3 pages) | Cited 42 times

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A microlaser, microgear, composed of a microdisk and a rotationally symmetric Bragg grating is described. A GaInAsP–InP device with μm radius was fabricated and the room-temperature continuous-wave operation was obtained by photopumping with a low threshold of 17 μW. The experiment clearly demonstrated that the Q factor in a microdisk was enhanced by the microgear due to the minimization of the radiation field. Resonant spectra showed some unique mode characteristics influenced by an elliptical cavity. These results suggest a potential of advanced engineering of whispering-gallery-mode laser with a photonic crystal, the generalized Bragg grating. © 2002 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
42.79.Dj Gratings
42.55.Px Semiconductor lasers; laser diodes
42.70.Qs Photonic bandgap materials
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Low temperature growth of InGaAs layers on misoriented GaAs substrates by metalorganic vapor phase epitaxy

Y. Takano, K. Kobayashi, H. Iwahori, N. Kuroyanagi, K. Kuwahara, S. Fuke, and S. Shirakata

Appl. Phys. Lett. 80, 2054 (2002); http://dx.doi.org/10.1063/1.1463210 (3 pages) | Cited 4 times

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InGaAs layers with In composition of 0.57 were grown with metalorganic vapor phase epitaxy (MOVPE) using graded buffer layers on exactly oriented and misoriented GaAs(100) substrates. No mirror-like surface was obtained at growth temperatures between 570 °C and 630 °C. A mirror-like surface was achieved at a growth temperature of 450 °C. The threading dislocation density in the layer grown at 450 °C on the GaAs substrate misoriented toward (111)A was determined to be 1×107 cm−2 using transmission electron microscopy. Photoluminescence results also confirmed that the density of recombination centers in layers grown at 450 °C was low. Low temperature growth with MOVPE was found to be effective in InGaAs layers on GaAs substrates with high In composition above 0.4. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Fd III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
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
68.37.Lp Transmission electron microscopy (TEM)
78.55.Cr III-V semiconductors

Fabrication of a low-threading-dislocation-density AlxGa1−xN buffer on SiC using highly Si-doped AlxGa1−xN superlattices

Hideki Hirayama, Makoto Ainoya, Atsuhiro Kinoshita, Akira Hirata, and Yoshinobu Aoyagi

Appl. Phys. Lett. 80, 2057 (2002); http://dx.doi.org/10.1063/1.1457523 (3 pages) | Cited 6 times

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An in situ technique to reduce the threading dislocation density (TDD) of an AlxGa1−xN buffer within submicron-thick growth is demonstrated using metalorganic vapor-phase epitaxy. We achieved a marked reduction in the TDD of the AlGaN buffer on a SiC substrate by inserting superlattices (SLs) consisting of highly Si-doped AlGaN and undoped AlGaN layers. The TDD of AlGaN decreased from 2×1010 to 7×107 cm−2 by inserting SLs with total growth thickness of 0.8 μm. The Si incorporation in the highly Si-doped AlGaN layers of the SLs was estimated to be approximately 1.2×1020 cm−3 (0.24%). This is strictly an in situ technique that does not require complicated fabrication processes, and the surface is kept flat throughout the entire growth. This method is especially useful on SiC wafers to prevent cracks in a thin growth layer. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.61.Ey III-V semiconductors
68.65.Cd Superlattices

In situ diffuse reflectance spectroscopy investigation of low-temperature-grown GaAs

Ri-an Zhao, Michael J. Cich, Petra Specht, and Eicke R. Weber

Appl. Phys. Lett. 80, 2060 (2002); http://dx.doi.org/10.1063/1.1463215 (3 pages) | Cited 3 times

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We have utilized in situ diffuse reflectance spectroscopy (DRS) to monitor both the substrate temperature transient and the epilayer absorption during low-temperature (LT) GaAs molecular-beam epitaxy. We have found a significant increase of the sub-band-gap absorption from LT GaAs. The magnitude of absorption at 1.2 eV correlates well with the concentration of arsenic antisite defects. The incorporation rate of arsenic antisites appears uniform despite a substrate temperature transient due to the effusion cell radiation heating. The influence of absorption spectra change on the accuracy of DRS temperature measurement is also discussed. This study shows that DRS can be used for both growth temperature measurement and real-time nonstoichiometry monitoring. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.30.Fs III-V and II-VI semiconductors
07.20.Dt Thermometers

Bandtail characteristics in InN thin films

W. Z. Shen, L. F. Jiang, H. F. Yang, F. Y. Meng, H. Ogawa, and Q. X. Guo

Appl. Phys. Lett. 80, 2063 (2002); http://dx.doi.org/10.1063/1.1464219 (3 pages) | Cited 38 times

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The Urbach bandtail characteristics in InN thin films grown by radio-frequency magnetron sputtering on sapphire (0001) substrates have been investigated both theoretically and experimentally. The bandtail parameter in InN thin films has been obtained by temperature-dependent transmission spectra, with the aid of a detailed calculation of the transmission profile. A bandtail model based on the calculation of density of occupied states and the carrier–phonon interaction has been employed to analyze the temperature-dependent bandtail characteristics. The bandtail parameter is in the range of 90–120 meV in the InN thin film. It is found that the carrier–phonon interaction in InN is weak and the structural disorder contribution ( ∼ 90 meV) dominates over the interactive terms. The high structural disorder in InN thin films may relate to the high nonradiative recombination centers. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
71.20.Nr Semiconductor compounds
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
71.55.Jv Disordered structures; amorphous and glassy solids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering

Concurrent evaluation of strain in heteroepitaxial thin films with continuous lattice mismatch spread

M. Ohtani, T. Fukumura, M. Kawasaki, K. Omote, T. Kikuchi, J. Harada, and H. Koinuma

Appl. Phys. Lett. 80, 2066 (2002); http://dx.doi.org/10.1063/1.1462871 (3 pages) | Cited 7 times

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We have developed a way to map out concurrently the in-plane lattice constant of a heteroepitaxial thin film with a spatial resolution of 0.1 mm by using concurrent x-ray diffractometer equipped with a convergent x-ray source and two-dimensional detector. Spatial distribution of heteroepitaxial strain is analyzed for a (BaxSr1−x)TiO3 composition-spread thin film grown on a SrTiO3 substrate. As x increases, elastic deformation caused by compressive stress due to the lattice mismatch forces the lattice of the film to be coherent with that of the substrate until a critical point of x = 0.6, above which the film lattice relaxes. By just taking three snap shots of x-ray diffraction image at a symmetric and two asymmetric diffraction configurations, such useful information inherent in heteroepitaxy can be revealed. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
62.20.D- Elasticity
68.55.-a Thin film structure and morphology
61.50.Lt Crystal binding; cohesive energy

Extremely low critical cooling rate measured on dispersed Pd43Ni10Cu27P20

Jan Schroers and William L. Johnson

Appl. Phys. Lett. 80, 2069 (2002); http://dx.doi.org/10.1063/1.1462861 (3 pages) | Cited 15 times

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Crystallization of dispersed Pd43Ni10Cu27P20 melts is studied during constant cooling and heating. Investigations are carried out on samples that are dispersed into several hundred particles which are fluxed in B2O3. The size of the particles is chosen in such a way that crystallization of individual particles can be observed. Constant cooling experiments with rates between 0.3 and 0.0016 K/s are performed. In order to determine the fraction of particles that crystallize upon cooling, the crystallization during subsequent heating at 0.3 K/s is utilized. 10%–15% of the particles do not crystallize during cooling with a rate as low as 0.005 K/s. This is the lowest rate that avoids crystallization ever measured for a metallic system. This extremely low critical cooling rate suggests that a fraction of the particles do not contain the impurities that act as nuclei in bulk samples. Therefore, in these particles, nuclei first have to form and crystallization does not take place, as it was found for bulk Pd43Ni10Cu27P20, by the growth on pre-existing nuclei formed by impurities. © 2002 American Institute of Physics.
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64.70.D- Solid-liquid transitions

Thermal annealing effect on nitrogen vacancy in proton-irradiated AlxGa1−xN

Qiaoying Zhou and M. O. Manasreh

Appl. Phys. Lett. 80, 2072 (2002); http://dx.doi.org/10.1063/1.1463703 (3 pages) | Cited 8 times

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The optical absorption band associated with the nitrogen vacancy in proton-irradiated AlxGa1−xN, for x = 0.61 and 1, is investigated under isothermal furnace annealing in the temperature range of 150–350 °C. The results show that the enthalpy associated with the thermal migration process is 0.410±0.023 and 0.445±0.037 eV for Al0.61Ga0.39N and AlN, respectively. The variation of the full width at half maximum (FWHM) of the nitrogen vacancy absorption band in AlN as a function of temperature indicates that the electronic transition associated with the defect is coupled to a phonon with an energy of 47.8 meV. This phonon energy is in good agreement with the E2 phonon mode reported for AlN. A Frank–Condon shift of 1.142 eV is also estimated from the FWHM measured as a function of temperature, which is indicative of a large lattice distortion in the vicinity of the defect. © 2002 American Institute of Physics.
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61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
61.80.Jh Ion radiation effects
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.40.Fy Semiconductors

Effect of nitrogen and temperature on the electronic band structure of GaAs1−xNx alloys

R. Chtourou, F. Bousbih, S. Ben Bouzid, F. F. Charfi, J. C. Harmand, G. Ungaro, and L. Largeau

Appl. Phys. Lett. 80, 2075 (2002); http://dx.doi.org/10.1063/1.1462864 (3 pages) | Cited 24 times

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We have studied the band-gap reduction of GaAs1−xNx alloys with N contents between 0.1% and 1.5% using the absorption measurements in a series of samples grown by molecular-beam epitaxy. At room temperature, we observed a redshift of the band edge of about 205 meV for 1% of nitrogen. To interpret this effect, we assume that the incorporation of nitrogen in GaAs breaks the symmetry of the system and introduces localized N states that are weakly coupled to the extended states of the semiconductor. We have also studied the temperature dependence of the band gap of GaAsN alloys. The band-gap energy difference between 15 and 300 K decreases from 110 meV for GaAs, to 70 meV for GaAs0.985N0.015. All these experimental results can be explained by the band anticrossing model [W. Shan et al., Phys. Status Solidi B 223, 75 (2001)] with a coupling constant CNM of 2.7 eV, taking into account the contribution of tensile strain to the band-gap reduction. © 2002 American Institute of Physics.
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71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors

Structural and optical properties of epitaxial and bulk ZnO

A. Zeuner, H. Alves, D. M. Hofmann, B. K. Meyer, M. Heuken, J. Bläsing, and A. Krost

Appl. Phys. Lett. 80, 2078 (2002); http://dx.doi.org/10.1063/1.1464218 (3 pages) | Cited 43 times

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In this letter, we compare the properties of bulk and epitaxial ZnO. The ZnO thin films were grown on GaN templates and on ZnO single crystals by vapor phase deposition using Zn and NO2 as precursors. We use high-resolution x-ray diffraction to resolve the structural properties. The rocking curves of the bulk crystal are extremely broad caused by a mosaic structure of the substrate. The homoepitaxial ZnO film mimics the properties of the ZnO substrate whereas ZnO films on GaN templates showed superior rocking curve half width as small as 230 arcsec. The optical properties are investigated by temperature-dependent photoluminescence. Different donor and acceptor bound excitons can be distinguished for a half width of the recombination lines less than 1 meV. Free exciton emission is already detectable at liquid-He temperatures proofing the high quality of the epitaxial films. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
71.35.-y Excitons and related phenomena
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Preferential formation of Al☒N bonds in low N-content AlGaAsN

T. Geppert, J. Wagner, K. Köhler, P. Ganser, and M. Maier

Appl. Phys. Lett. 80, 2081 (2002); http://dx.doi.org/10.1063/1.1464660 (3 pages) | Cited 24 times

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The bonding of nitrogen in low N-content AlxGa1−xAs1−yNy with x ⩽ 0.05 and y ⩽ 0.04 has been studied by Raman spectroscopy. Upon the addition of Al to GaAsN, additional vibrational modes are observed at around 450 cm−1, which is below the GaN-like longitudinal optical (LO) phonon mode centered at 470 cm−1. These modes are attributed to the formation of Al and N containing complexes with Al-to-N bonding. With increasing Al content the Al–N related modes gain intensity at the expense of the GaN-like mode, and they become the dominant N-related feature for an Al-content of 5% at a fixed N content of 1%. On the other hand, increasing the N content from 0% up to 4% at a constant Al concentration of 5% results first in the appearance and eventual saturation in intensity of the AlN-like modes, accompanied by a steep increase in intensity and eventual dominance of the GaN-like vibrational mode. Simultaneously the AlAs-like LO2 phonon mode shows a drastic decrease in intensity for N contents exceeding 2%. All these observations strongly indicate that there is a preferential formation of Al☒N bonds in low N- and Al-content AlGaAsN, which is in direct contrast to GaInAsN, where even after thermal annealing the GaN-like mode remains dominant in the Raman spectrum compared to the InN-like modes. © 2002 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
61.50.Lt Crystal binding; cohesive energy
61.72.Cc Kinetics of defect formation and annealing
78.30.Fs III-V and II-VI semiconductors

Lateral displacement of a Gaussian beam reflected from a grounded slab with negative permittivity and permeability

Jin Au Kong, Bae-Ian Wu, and Yan Zhang

Appl. Phys. Lett. 80, 2084 (2002); http://dx.doi.org/10.1063/1.1462865 (3 pages) | Cited 63 times

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A unique negative lateral shift is demonstrated in this letter for a Gaussian beam reflected from a grounded slab with both negative permittivity and permeability, which is distinctly different from a shift caused by a regular grounded slab. The incident beam is modeled as a tapered wave with a Gaussian spectrum. The waves inside and outside the slab are solved analytically from Maxwell’s equations by matching the boundary conditions at the interfaces. It is shown that the field values in all regions can be unambiguously determined. Numerical simulations are presented and the field values as well as the power densities are computed for all regions, and a dramatic negative lateral shift is observed when both ϵ and μ are negative. © 2002 American Institute of Physics.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
03.50.De Classical electromagnetism, Maxwell equations
42.25.Gy Edge and boundary effects; reflection and refraction

Temperature-dependent photoluminescence of high-quality GaInNAs single quantum wells

Sho Shirakata, Masahiko Kondow, and Takeshi Kitatani

Appl. Phys. Lett. 80, 2087 (2002); http://dx.doi.org/10.1063/1.1463208 (3 pages) | Cited 28 times

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Temperature dependence of the near-bandedge photoluminescence (PL) was studied on a 10-nm Ga0.68In0.32N0.01As0.99/GaAs single quantum well (SQW) prepared by molecular-beam epitaxy for both the as-grown and the rapid-thermal-annealed (RTA) samples. Full width at half maximum (FWHM) value was 18–26 meV (for 80–280 K) and 11–19 meV (for 8–280 K) for the as-grown and the RTA samples, respectively. The FWHM of the RTA sample is the smallest among the samples prepared before and those reported so far. At low temperature (8–50 K), a PL peak due to the localized level was observed for the as-grown sample. However, no such peak was observed for the RTA sample. The PL intensity of the RTA sample was about 10–100 times larger than that of similar SQWs grown previously. These results indicate that the crystal quality of the RTA GaInNAs SQW used in this study is both outstanding and comparable with that of the corresponding GaInAs SQW. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
61.72.Cc Kinetics of defect formation and annealing

Change of quasilattice constant during amorphous-to-quasicrystalline phase transformation in Zr65Al7.5Ni10Cu7.5Ag10 metallic glass

J. Z. Jiang, A. R. Rasmussen, C. H. Jensen, Y. Lin, and P. L. Hansen

Appl. Phys. Lett. 80, 2090 (2002); http://dx.doi.org/10.1063/1.1463207 (3 pages) | Cited 10 times

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The amorphous-to-quasicrystalline phase transformation in a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass has been investigated by monitoring the quasilattice constant and the composition of quasicrystalline particles in the samples annealed in vacuum at 663 K for various times. It is found that the quasilattice constant decreases with annealing time and saturates after 90 min while the zirconium and silver contents in quasicrystalline particles differ from those in the remaining amorphous matrix. The results provide evidence that the amorphous-to-quasicrystalline phase transformation in the Zr65Al7.5Ni10Cu7.5Ag10 metallic glass is a nonpolymorphous reaction. © 2002 American Institute of Physics.
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61.44.Br Quasicrystals
64.70.K- Solid-solid transitions
61.43.Fs Glasses
61.43.Dq Amorphous semiconductors, metals, and alloys

Intraband absorption and photocurrent spectroscopy of self-assembled p-type Si/SiGe quantum dots

T. Fromherz, W. Mac, A. Hesse, G. Bauer, C. Miesner, K. Brunner, and G. Abstreiter

Appl. Phys. Lett. 80, 2093 (2002); http://dx.doi.org/10.1063/1.1458531 (3 pages) | Cited 12 times

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In infrared transmission and photocurrent spectra of self-assembled SiGe quantum dot samples grown in the Stranski–Krastanow mode at temperatures around T = 520 °C different types of transitions are observed: in the transmission experiments, an absorption line due to bound-to-bound transitions is measured whereas the photocurrent spectra are determined by bound-to-continuum transitions. The experimental determination of the energies of both types of transitions for the same sample allows a detailed discussion of the features observed in the spectra as well as an estimate of the average Ge content in the dots. © 2002 American Institute of Physics.
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73.63.Kv Quantum dots
78.67.Hc Quantum dots
73.21.La Quantum dots
78.30.Am Elemental semiconductors and insulators
73.50.Pz Photoconduction and photovoltaic effects

Self-organized nanodot formation on MgO(100) by ion bombardment at high temperatures

M. Lu, X. J. Yang, S. S. Perry, and J. W. Rabalais

Appl. Phys. Lett. 80, 2096 (2002); http://dx.doi.org/10.1063/1.1464222 (3 pages) | Cited 12 times

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The production of self-organized, spatially dense nanodots on a MgO(100) surface by Ar+ bombardment at elevated sample temperatures (700 and 1000 °C) and ion energies in the range 0.5–5 keV is reported. The results show that at elevated temperatures, the size of the nanodots can be modified by varying the ion energy in a well-defined manner. The nanodot diameter is found to increase with increasing temperature and decrease with increasing ion flux and increasing ion energy. The dot diameter is several tens of nanometers and the height is several nanometers. These results can be interpreted in terms of a recently developed theoretical model. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.46.-w Structure of nanoscale materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators

Influence of metalorganic chemical vapor deposition growth conditions on In-rich nanoislands formation in InGaN/GaN structures

Yu. G. Musikhin, D. Gerthsen, D. A. Bedarev, N. A. Bert, W. V. Lundin, A. F. Tsatsul’nikov, A. V. Sakharov, A. S. Usikov, Zh. I. Alferov, I. L. Krestnikov, N. N. Ledentsov, A. Hoffmann, and D. Bimberg

Appl. Phys. Lett. 80, 2099 (2002); http://dx.doi.org/10.1063/1.1462868 (3 pages) | Cited 20 times

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The influence of different growth conditions on the In distribution in ultrathin InGaN insertions in a GaN matrix is investigated by high-resolution transmission electron microscopy and an appropriate image evaluation technique. It is demonstrated that the indium distribution represents dense arrays of In-rich nanodomains inserted in a layer with a lower indium concentration. The sizes of the In-rich regions are about 4–5 nm at a growth temperature of 720 °C. Increasing the growth temperature leads to a strong decrease in the of nanoisland density and, also, a moderate decrease in their lateral size. Increasing the trimethylindium/trimethylgallium ratio strongly increases the density of the islands, but the lateral size remains weakly effected. The observations are in agreement with a thermodynamic model of island formation including entropy effects. © 2002 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- Nucleation and growth
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
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High-mobility InSb epitaxial films grown on a GaAs (001) substrate using liquid-phase epitaxy

V. K. Dixit, Bhavtosh Bansal, V. Venkataraman, H. L. Bhat, G. N. Subbanna, K. S. Chandrasekharan, and B. M. Arora

Appl. Phys. Lett. 80, 2102 (2002); http://dx.doi.org/10.1063/1.1458066 (3 pages) | Cited 8 times

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The growth of epitaxial InSb layers on highly lattice-mismatched semi-insulating GaAs substrates has been achieved via traditional liquid-phase epitaxy. Scanning and transmission electron microscopy show sharp interfaces even at 35 nm resolution. High-resolution x-ray diffraction studies reveal reflections even up to 2θ = 153° with distinct layer and substrate peaks, indicating structural coherence. The films grown were n type and the highest electron mobility obtained was 3.96×104 cm2/V s at room temperature. The band gap varies from 0.17 to 0.23 eV in the temperature range of 300–10 K and is consistent with the expected variation. These results indicate that the films grown are comparable to those grown by other sophisticated techniques in terms of structural, optical and electrical properties. © 2002 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.61.Ey III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Closely spaced and separately contacted two-dimensional electron and hole gases by in situ focused-ion implantation

M. Pohlt, M. Lynass, J. G. S. Lok, W. Dietsche, K. v. Klitzing, K. Eberl, and R. Mühle

Appl. Phys. Lett. 80, 2105 (2002); http://dx.doi.org/10.1063/1.1463698 (3 pages) | Cited 15 times

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Separately contacted layers of a two-dimensional (2D) electron gas and a 2D hole gas have been prepared in GaAs, which are separated by AlGaAs barriers down to 15 nm thickness. The molecular-beam-epitaxial growth was interrupted just before growth of the double-layer structure in order to use in situ focused-ion-beam implantation to pattern contacts which extend underneath the barrier. The two charge gases form upon biasing the p- and n-type contacts underneath and above the barrier in the forward direction and show independent transistor-like behavior. © 2002 American Institute of Physics.
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73.21.Hb Quantum wires
73.61.Ey III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors

Characteristics of high-quality p-type AlxGa1−xN/GaN superlattices

A. Yasan, R. McClintock, S. R. Darvish, Z. Lin, K. Mi, P. Kung, and M. Razeghi

Appl. Phys. Lett. 80, 2108 (2002); http://dx.doi.org/10.1063/1.1463708 (3 pages) | Cited 10 times

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Very-high-quality p-type AlxGa1−xN/GaN superlattices have been grown by low-pressure metalorganic vapor-phase epitaxy through optimization of Mg flow and the period of the superlattice. For the superlattice with x = 26%, the hole concentration reaches a high value of 4.2×1018 cm−3 with a resistivity as low as 0.19 Ω cm by Hall measurement. Admittance spectroscopy was performed in order to investigate the electrical properties of the superlattices. These measurements confirm that superlattices with a larger period and higher Al composition have higher hole concentration and lower resistivity, as predicted by theory. © 2002 American Institute of Physics.
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73.63.Hs Quantum wells
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Structural instability of 4H–SiC polytype induced by n-type doping

J. Q. Liu, H. J. Chung, T. Kuhr, Q. Li, and M. Skowronski

Appl. Phys. Lett. 80, 2111 (2002); http://dx.doi.org/10.1063/1.1463203 (3 pages) | Cited 48 times

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Spontaneous formation of stacking faults in heavily nitrogen-doped 4H-polytype silicon carbide crystals have been observed by transmission electron microscopy (TEM). Faults were present in as-grown boules and additional faults were generated by annealing in argon at 1150 °C. All faults had identical structure consisting of six layers stacked in a cubic sequence as determined by high-resolution TEM, and were interpreted as a result of two Shockley partial dislocations gliding on two neighboring basal planes of SiC. It is argued that the energy of faulted 4H silicon carbide is lower than the energy of perfect heavily doped (n>1×1019 cm−3) crystal at typical processing temperatures, thus providing a driving force for transformation. © 2002 American Institute of Physics.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.Cc Kinetics of defect formation and annealing
78.55.Hx Other solid inorganic materials
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Role of nitrogen related complexes in the formation of defects in silicon

A. Karoui, F. Sahtout Karoui, A. Kvit, G. A. Rozgonyi, and D. Yang

Appl. Phys. Lett. 80, 2114 (2002); http://dx.doi.org/10.1063/1.1462874 (3 pages) | Cited 16 times

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Defect size and density distributions were obtained as a function of depth in nitrogen doped CZ silicon (N-CZ) following Hi–Lo–Hi and Lo–Hi annealing, using an oxygen precipitate profiler. The defects were also delineated by Wright etching and Nomarski optical microscopy on both cleaved and bevel polished samples. In addition to the enhanced precipitation and absence of voids previously reported for N-CZ Si, an unexpected mode of precipitation has been found near the annealed wafer surface, just above the traditional denuded zone. This oxynitride precipitate is discussed with regard to N-related complex interactions and point defect supersaturations/injection. High resolution transmission electron microscopy revealed that most precipitates have an octahedral shape with two distinct amorphous phases, which reflect a transition from an initial phase containing both N and O to one with primarily O, as verified with Z-contrast TEM and electron energy loss spectroscopy. © 2002 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
79.20.Uv Electron energy loss spectroscopy

Heteroepitaxial growth of CdTe on a p-Si(111) substrate by pulsed-light-assisted electrodeposition

Makoto Takahashi, Makoto Todorobaru, Koichi Wakita, and Kohei Uosaki

Appl. Phys. Lett. 80, 2117 (2002); http://dx.doi.org/10.1063/1.1463718 (3 pages) | Cited 5 times

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Highly oriented CdTe(111) films of high-crystalline quality were grown on a Si(111) substrate by pulsed-light-assisted electrodeposition at room temperature. Strong photoluminescence peaks due to the bound exciton recombination were observed for the electrodeposited CdTe films, confirming the high quality of the films prepared by the present method. Atomic-force microscopy measurements showed an atomically ordered arrangement and demonstrated the epitaxial growth of the CdTe films. © 2002 American Institute of Physics.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.15.Pq Electrodeposition, electroplating
81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.A- Nucleation and growth
73.20.At Surface states, band structure, electron density of states
71.35.-y Excitons and related phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
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