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25 Aug 2003

Volume 83, Issue 8, pp. 1497-1679

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1671 (2003); http://dx.doi.org/10.1063/1.1604161 (3 pages)

Wenyi Cai, Christopher F. Powell, Yong Yue, Suresh Narayanan, Jin Wang, Mark W. Tate, Matthew J. Renzi, Alper Ercan, Ernest Fontes, and Sol M. Gruner
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Strain relaxation in graded InGaN/GaN epilayers grown on sapphire

T. L. Song, S. J. Chua, E. A. Fitzgerald, P. Chen, and S. Tripathy

Appl. Phys. Lett. 83, 1545 (2003); http://dx.doi.org/10.1063/1.1598295 (3 pages) | Cited 9 times

Online Publication Date: 19 August 2003

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Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain that builds up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled, thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10-nm GaN layer grown at 750 °C and annealed at 1000 °C. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.65.Ac Multilayers
62.20.F- Deformation and plasticity
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.50.Lt Crystal binding; cohesive energy
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Radiation-induced nitrogen segregation during electron energy loss spectroscopy of silicon oxide–nitride-oxide stacks

Igor Levin, Richard D. Leapman, Mark Kovler, and Yakov Roizin

Appl. Phys. Lett. 83, 1548 (2003); http://dx.doi.org/10.1063/1.1604182 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2003

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Electron energy loss spectroscopy (EELS) in both fixed-probe transmission electron microscopy (TEM) and scanning TEM (STEM) was used to measure elemental profiles of Si, O, and N in the SiOx/SixNy/SiOx/poly-Si stacks deposited on silicon. The results revealed radiation-induced nitrogen segregation to both the Si/SiOx and SiOx/poly-Si interfaces; the extent of nitrogen segregation increased visibly with increasing the radiation dose. The nitrogen diffusion through the oxide layers apparently was accompanied by the diffusion of oxygen into the nitride. Low-noise artifact-free nitrogen profiles across the Si/SiOx interfaces were obtained in STEM by scanning the beam parallel to the layers. These measurements indicated lack of detectable nitrogen segregation to the interfaces. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
68.35.Dv Composition, segregation; defects and impurities
64.75.-g Phase equilibria
68.49.Jk Electron scattering from surfaces
68.37.Lp Transmission electron microscopy (TEM)
73.61.Ng Insulators

Luminescence of GaN nanocolumns obtained by photon-assisted anodic etching

I. M. Tiginyanu, V. V. Ursaki, V. V. Zalamai, S. Langa, S. Hubbard, D. Pavlidis, and H. Föll

Appl. Phys. Lett. 83, 1551 (2003); http://dx.doi.org/10.1063/1.1605231 (3 pages) | Cited 30 times

Online Publication Date: 19 August 2003

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GaN nanocolumns with transverse dimensions of about 50 nm were obtained by illumination-assisted anodic etching of epilayers grown by metalorganic chemical vapor deposition on sapphire substrates. The photoluminescence spectroscopy characterization shows that the as-grown bulk GaN layers suffer from compressive biaxial strain of 0.5 GPa. The majority of nanocolumns are fully relaxed from strain, and the room-temperature luminescence is free excitonic. The high quality of the columnar nanostructures evidenced by the enhanced intensity of the exciton luminescence and by the decrease of the yellow luminescence is explained by the peculiarities of the anodic etching processing. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.07.Bc Nanocrystalline materials
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
68.65.La Quantum wires (patterned in quantum wells)
81.65.Cf Surface cleaning, etching, patterning
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
61.82.Fk Semiconductors
62.25.-g Mechanical properties of nanoscale systems

Structural and morphological characteristics of planar (11math0) a-plane gallium nitride grown by hydride vapor phase epitaxy

B. A. Haskell, F. Wu, S. Matsuda, M. D. Craven, P. T. Fini, S. P. DenBaars, J. S. Speck, and Shuji Nakamura

Appl. Phys. Lett. 83, 1554 (2003); http://dx.doi.org/10.1063/1.1604174 (3 pages) | Cited 67 times

Online Publication Date: 19 August 2003

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This letter discusses the structural and morphological characteristics of planar, nonpolar (11math0) a-plane GaN films grown on (1math02) r-plane sapphire by hydride vapor phase epitaxy. Specular films with thicknesses over 50 μm were grown, eliminating the severely faceted surfaces that have previously been observed for hydride vapor phase epitaxy-grown a-plane films. Internal cracks and crack healing, similar to that in c-plane GaN films, were observed. Atomic force microscopy revealed nanometer-scale pitting and steps on the film surfaces, with rms roughness of ∼2 nm. X-ray diffraction confirmed the films are solely a-plane oriented with on-axis (11math0) and 30° off-axis (10math0) rocking curve peak widths of 1040 and 3000 arcsec, respectively. Transmission electron microscopy revealed a typical basal plane stacking fault density of 4×105 cm−1. The dislocation content of the films consisted of predominately edge component (bedge = ±[0001]) threading dislocations with a density of 2×1010 cm−2, and mixed-character Shockley partial dislocations (b = ⅓〈1math00〉) with a density of 7×109 cm−2. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Fast optical nonlinearity induced by space-charge waves in dc-biased GaAs

L. Subačius, I. Kašalynas, R. Aleksiejūnas, and K. Jarašiūnas

Appl. Phys. Lett. 83, 1557 (2003); http://dx.doi.org/10.1063/1.1604180 (3 pages) | Cited 3 times

Online Publication Date: 19 August 2003

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Time-resolved four-wave mixing in dc-biased GaAs crystals exhibit GHz frequency oscillations when the applied dc field and nonequilibrium carrier density are high enough to form a photorefractive high-field domain grating. Its propagation through the spatially modulated carrier density structure creates a photorefractive space-charge wave and leads to an oscillatory behavior of the probe-beam diffraction efficiency with period T = Λ/ν ≈ 200 ps, determined by the grating spacing Λ and domain drift velocity ν. Formation of the space-charge wave in dc-biased GaAs was verified experimentally by using a picosecond transient grating technique. The experimental data were found to be in good agreement with numerical calculations based on the hot electron hydrodynamic model. © 2003 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
78.20.Jq Electro-optical effects
72.20.Ht High-field and nonlinear effects

Birefringent control and optical switching of copolymer liquid crystal film with azobenzene and photocrosslinkable side groups

Nobuhiro Kawatsuki and Emi Uchida

Appl. Phys. Lett. 83, 1560 (2003); http://dx.doi.org/10.1063/1.1604940 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2003

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Photocontrol and optical switching of birefringence (Δn) in a poly(methacrylate) copolymer liquid crystal films substituted with 4-methoxyazobenzene and 4(4-methoxycinnamoyloxy)biphenyl side groups are described. Irradiating with linearly polarized 365 nm light and subsequently annealing generated uniaxial in-plane orientation of the films. Adjusting the exposure doses of nonpolarized (NP) 405 nm light regulated the generated Δn of 0.26–0.13, and after reannealing the initial value is completely restored. Optical control of the birefringence with response times of 50 ms is demonstrated when the films are exposed to NP 405 nm light at elevated temperatures. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.Fm Birefringence
42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.Vx Polymer liquid crystals

Epitaxial CuIn(1−x)GaxS2 on Si(111): A perfectly lattice-matched system for x ≈ 0.5

H. Metzner, J. Cieslak, J. Eberhardt, Th. Hahn, M. Müller, U. Kaiser, A. Chuvilin, U. Reislöhner, W. Witthuhn, R. Goldhahn, F. Hudert, and J. Kräußlich

Appl. Phys. Lett. 83, 1563 (2003); http://dx.doi.org/10.1063/1.1605239 (3 pages) | Cited 2 times

Online Publication Date: 19 August 2003

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We demonstrate the direct heteroepitaxial growth of the quaternary semiconductor CuIn(1−x)GaxS2 on Si(111) substrates by means of molecular-beam epitaxy. Using Rutherford backscattering, x-ray diffraction, transmission electron microscopy, and photoreflectance, samples of various Ga contents, x, were characterized in detail. Epitaxial growth was achieved in the whole compositional range and perfect lattice match between the epitaxial layer and substrate was obtained for x ≈ 0.5. The epitaxial layers show the coexistence of bulk chalcopyrite and metastable CuAu-type cation ordering. Photoreflectance data reveal a linear increase of the fundamental band gap with increasing Ga content. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
85.40.Sz Deposition technology
71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.37.Lp Transmission electron microscopy (TEM)

Crystal growth in colloidal tin oxide nanocrystals induced by coalescence at room temperature

E. R. Leite, T. R. Giraldi, F. M. Pontes, E. Longo, A. Beltrán, and J. Andrés

Appl. Phys. Lett. 83, 1566 (2003); http://dx.doi.org/10.1063/1.1605241 (3 pages) | Cited 87 times

Online Publication Date: 19 August 2003

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The crystal growth process in colloidal nanocrystal systems is usually associated with the Ostwald-ripening mechanism. Here, we report on experimental evidence indicating that another crystal growth process took place in a colloidal nanocrystal system at room temperature. This crystal growth process is based on grain rotation among neighboring grains, resulting in a coherent grain–grain interface, which, by eliminating common boundaries, causes neighboring grains to coalesce, thereby forming a single larger nanocrystal. This phenomenon was observed in SnO2 nanocrystals (particle size ranging from 10 to 30 Å). © 2003 American Institute of Physics.
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81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
81.07.Bc Nanocrystalline materials
82.70.Dd Colloids
61.46.-w Structure of nanoscale materials

Structural anisotropy in GaN films grown on vicinal 4H-SiC surfaces by metallorganic molecular-beam epitaxy

Jun-ichi Kato, Satoru Tanaka, Satoshi Yamada, and Ikuo Suemune

Appl. Phys. Lett. 83, 1569 (2003); http://dx.doi.org/10.1063/1.1605791 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2003

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GaN grown directly on 4H-SiC substrates by metallorganic molecular-beam epitaxy is investigated in terms of nucleation, coalescence, and growth front evolution. The effects of SiC surface configurations such as step and terrace structures on GaN film growth physics are examined in detail. Comparative studies using on-axis and vicinal SiC surfaces indicate distinguishable differences in structural and morphological characteristics. An anisotropic x-ray characteristic is observed for the GaN film deposited on the vicinal stepped SiC surfaces. This is due to preferential nucleation and coalescence of GaN islands along step edges, which are induced by the confinement of adatoms on the narrow terraces on the vicinal SiC surface. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
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