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23 Jun 2003

Volume 82, Issue 25, pp. 4411-4611

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 4322 (2003); http://dx.doi.org/10.1063/1.1582366 (3 pages)

Hongwei Qu, Wei Yao, T. Garcia, Jiandi Zhang, A. V. Sorokin, S. Ducharme, P. A. Dowben, and V. M. Fridkin
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Liquid crystal alignment surface with two easy axes induced by unidirectional rubbing

Rumiko Yamaguchi, Yusuke Goto, and Susumu Sato

Appl. Phys. Lett. 82, 4450 (2003); http://dx.doi.org/10.1063/1.1585128 (3 pages) | Cited 3 times

Online Publication Date: 16 June 2003

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We report the liquid crystal (LC) alignment surface which has two orthogonal easy axes induced by a unidirectional rubbing treatment. When the photoreactive polymer with chalconyl sidechains is irradiated with nonpolarized UV light and subsequently rubbed with a cloth, LCs align parallel and perpendicular to the rubbing direction on the UV irradiated and nonirradiated surfaces, respectively. The polarized UV absorption of the polymer and the sign of the dichroism are measured to explain the alignment mechanism. The micropatterning of the LC alignment is successfully demonstrated through the simple process using a photomask and nonpolarized UV irradiation technique. © 2003 American Institute of Physics.
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61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
42.70.Df Liquid crystals
78.20.Fm Birefringence

Evolution of the electron localization in a nonconventional alloy system GaAs1−xNx probed by high-magnetic-field photoluminescence

Y. J. Wang, X. Wei, Y. Zhang, A. Mascarenhas, H. P. Xin, Y. G. Hong, and C. W. Tu

Appl. Phys. Lett. 82, 4453 (2003); http://dx.doi.org/10.1063/1.1584789 (3 pages) | Cited 10 times

Online Publication Date: 16 June 2003

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We demonstrate that a high magnetic field can be used effectively not only to probe the nature of the photoluminescence (PL) in a semiconductor, but also to reveal emission peaks that are unobservable at zero field since the magnetic field can alter energy relaxation processes and the statistical distribution of the photocarriers. Our systematic magneto-PL study of GaAs1−xNx (0.1% ⩽ x<2.5%) in fields up to 30 T indicates that the character of the low-temperature PL in this system changes drastically with varying nitrogen composition x and exhibits transitions with applying strong magnetic fields. For x<0.7%, the PL spectrum shows many discrete features whose energies remain nearly stationary up to the highest applied field. However, the magnetic confinement gives rise to a feature emerging on the higher energy side of the zero-field spectrum. This feature does show a diamagnetic shift, but it is much slower that that of the GaAs band-edge transition. For x>1%, the PL spectrum evolves into a broad band, and its diamagnetic shift resembles the band-edge transition in a conventional semiconductor, and the rate of shift is comparable to that of GaAs. From the diamagnetic shift of the band, the reduced effective masses for different composition of nitrogen have been derived for this system using the standard theory for the magneto-exciton in a three dimensional semiconductor. © 2003 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.20.Ls Magneto-optical effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.35.Ji Excitons in magnetic fields; magnetoexcitons

Strong ultraviolet emission from SiO2/LiNbO3(:Fe)/SiO2 structures

X. Yang, X. L. Wu, W. W. Xue, G. S. Huang, G. G. Siu, Z. G. Dong, L. Fang, and M. R. Shen

Appl. Phys. Lett. 82, 4456 (2003); http://dx.doi.org/10.1063/1.1586789 (3 pages) | Cited 4 times

Online Publication Date: 16 June 2003

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SiO2/LiNbO3(LN)/SiO2 sandwich structures were fabricated for exploring efficient light emission. After annealing at 1000 °C in O2 for 30 min, this kind of sandwich structure shows a strong ultraviolet photoluminescence (PL) with an asymmetric spectral shape. This PL spectrum may be Gaussian divided into two bands peaked at 310 (α-band) and 346 nm (β-band). If the layer of LN film is replaced by an Fe-doped LN (LN:Fe) one, the β-band vanishes and the α-band redshifts. The α-band is greatly enhanced and simultaneously becomes asymmetrical after this kind of SiO2/LN:Fe/SiO2 structure is annealed for 60 min. Spectral analysis suggests that the α-band arises from an optical transition in positively charged E′ centers at the interfaces between the LN(:Fe) film and the two SiO2 layers, while the β-band arises from intrinsic defects in the LN(:Fe) films. The mechanism for the PL enhancement is discussed in terms of a photorefractive effect in the LN(:Fe) films. © 2003 American Institute of Physics.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
42.79.Wc Optical coatings
81.40.Tv Optical and dielectric properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Nonuniform current distribution in metal/diamond/metal vertical structures

G. Conte, M. C. Rossi, S. Salvatori, F. Tersigni, P. Ascarelli, and E. Cappelli

Appl. Phys. Lett. 82, 4459 (2003); http://dx.doi.org/10.1063/1.1583855 (3 pages) | Cited 6 times

Online Publication Date: 16 June 2003

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The role of grain boundaries (GBs) in undoped polycrystalline diamond films has been investigated by dc and ac electrical measurements in a wide temperature range. Hopping transport along GB percolating paths and field-assisted thermal ionization of trapped charges are observed at low and high electric field strength, respectively. The temperature dependence of the ac conductivity, which reduces to a universal curve according to a random free-energy barrier model, suggests that, at low field strengths, current flow is mainly confined into GB domains in a wide temperature range. Only in the high-temperature and high-field ranges, do crystalline diamond grains become involved in current transport. © 2003 American Institute of Physics.
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73.40.Sx Metal-semiconductor-metal structures
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Mm Grain and twin boundaries

Subwavelength ripple formation on the surfaces of compound semiconductors irradiated with femtosecond laser pulses

A. Borowiec and H. K. Haugen

Appl. Phys. Lett. 82, 4462 (2003); http://dx.doi.org/10.1063/1.1586457 (3 pages) | Cited 148 times

Online Publication Date: 16 June 2003

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High-spatial-frequency periodic structures on the surfaces of InP, GaP, and GaAs have been observed after multiple-pulse femtosecond laser irradiation at wavelengths in the transparency regions of the respective solids. The periods of the structures are substantially shorter than the wavelengths of the incident laser fields in the bulk materials. In contrast, high-frequency structures were not observed for laser photon energies above the band gaps of the target materials. © 2003 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Shortest intersubband transition wavelength (1.68 μm) achieved in AlN/GaN multiple quantum wells by metalorganic vapor phase epitaxy

Ichitaro Waki, Chaiyasit Kumtornkittikul, Yukihiro Shimogaki, and Yoshiaki Nakano

Appl. Phys. Lett. 82, 4465 (2003); http://dx.doi.org/10.1063/1.1586473 (3 pages) | Cited 29 times

Online Publication Date: 16 June 2003

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Two-hundred-period high-quality AlN/GaN multiple quantum wells (MQWs) grown by metalorganic vapor phase epitaxy are studied using high-resolution x-ray diffraction, transmission electron microscopy, and optical transmission spectroscopy. Excellent interfaces of the MQWs are confirmed by these measurements. The strong intersubband absorption peak at a wavelength of 1.68 μm is achieved for AlN (1.6 nm)/GaN(1.7 nm) MQW. The full width at half-maximum of the absorption peak is estimated to be 27 meV. © 2003 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
78.30.Fs III-V and II-VI semiconductors
68.65.Fg Quantum wells

Interface energy of Au7Si grown in the interfacial layer of truncated hexagonal dipyramidal Au nanoislands on polycrystalline-silicon

J. S. Wu, Y. F. Chen, S. Dhara, C. T. Wu, K. H. Chen, and L. C. Chen

Appl. Phys. Lett. 82, 4468 (2003); http://dx.doi.org/10.1063/1.1586997 (3 pages) | Cited 7 times

Online Publication Date: 16 June 2003

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Growth of truncated hexagonal dipyramidal Au nanoislands is reported by annealing Au/amorphous-Si/crystalline-Si at 1030 °C in oxygen and nitrogen ambient. Metastable gold silicide phase of Au7Si is observed to form at the interface of Au and polycrystalline Si, which was transformed from amorphous Si. Oxygen, acting as an impurity, inhibits outdiffusion of Si at the interface and thus controls the growth of Si deficient metastable phase of Au7Si in a diffusion-limited growth process. Interface energies of Au7Si (0.623–0.672 N/m) and Au–Au7Si (1.438–1.471 N/m) are derived from the contact angle measurements of the island structure involving Au and Au7Si. © 2003 American Institute of Physics.
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68.35.Md Surface thermodynamics, surface energies
68.35.Ct Interface structure and roughness

Inversion domains and pinholes in GaN grown over Si(111)

A. M. Sánchez, P. Ruterana, M. Benamara, and H. P. Strunk

Appl. Phys. Lett. 82, 4471 (2003); http://dx.doi.org/10.1063/1.1584072 (3 pages) | Cited 6 times

Online Publication Date: 16 June 2003

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High-resolution transmission electron microscopy is used to analyze the connection between pinholes and inversion domains at the AlN/GaN interface. From some pinholes on top of the AlN buffer layer, the subsequent growth of GaN was observed to lead to the formation of inversion domains. In addition, the pinhole area which was originally the termination of defects from the buffer layer is highly strained and its boundary facets in {11math2} and {11math3} atomic planes. Inside the GaN the inversion domain boundary quickly settles to the usual {10math0} planes. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Early manifestation of localization effects in diluted Ga(AsN)

F. Masia, A. Polimeni, G. Baldassarri Höger von Högersthal, M. Bissiri, M. Capizzi, P. J. Klar, and W. Stolz

Appl. Phys. Lett. 82, 4474 (2003); http://dx.doi.org/10.1063/1.1586787 (3 pages) | Cited 35 times

Online Publication Date: 16 June 2003

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The electron effective mass, me, and extent of exciton wave function, rexc, were derived in GaAs1−yNy (y = 0.043%–0.5%) from magnetophotoluminescence measurements. With an increase in nitrogen concentration, we find that me and rexc undergo a rapid increase and squeezing, respectively, even for y ≈ 0.1%. This quite early manifestation of nitrogen-induced localization effects imposes important constraints on existing theoretical models. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.35.Ji Excitons in magnetic fields; magnetoexcitons
78.55.Cr III-V semiconductors
78.20.Ls Magneto-optical effects

Effect of InGaAs capping layer on the properties of InAs/InGaAs quantum dots and lasers

F. Y. Chang, C. C. Wu, and H. H. Lin

Appl. Phys. Lett. 82, 4477 (2003); http://dx.doi.org/10.1063/1.1585125 (3 pages) | Cited 17 times

Online Publication Date: 16 June 2003

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We report the effects of In0.33Ga0.67As capping layers on the structural and optical properties of InAs self-organized quantum dots grown by gas-source molecular-beam epitaxy. With different deposition methods for the InGaAs capping layer, the quantum-dot density can be adjusted from 2.3×1010 to 1.7×1011 cm−2. As-cleaved 3.98-mm-long diode laser using triple stacks of InAs quantum dots with the capping layer grown by GaAs/InAs sequential binary growth demonstrates an emission wavelength of 1305 nm and a threshold current density of 360 A/cm2. A ground-state saturation gain of 16.6 cm−1 is achieved due to the high dot density. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Formation of patterned buried insulating layer in Si substrates by He+ implantation and annealing in oxidation atmosphere

Atsushi Ogura

Appl. Phys. Lett. 82, 4480 (2003); http://dx.doi.org/10.1063/1.1586783 (3 pages) | Cited 4 times

Online Publication Date: 16 June 2003

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We fabricated patterned buried insulating layers in a Si substrate by implanting He+ ions through a patterned mask and annealing in an oxidation atmosphere. Compared with patterned O+ implantation and annealing, this technique causes less damage, and can therefore reduce defect density at the edge of the patterned buried insulator. The buried insulator could be SiO2 or a void with thin SiO2 film on the inner surface. The formation of a void could further reduce defect density, probably because the stress induced by SiO2 formation is small. The fabricated surface was extremely smooth within the focal depth limitations of state-of-the-art photolithography techniques. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
61.80.Jh Ion radiation effects
81.65.Mq Oxidation
85.40.Hp Lithography, masks and pattern transfer
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
73.20.At Surface states, band structure, electron density of states
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Interface-reaction-mediated formation of two-dimensional Si islands on CaF2

Andreas Klust, Michael Grimsehl, and Joachim Wollschläger

Appl. Phys. Lett. 82, 4483 (2003); http://dx.doi.org/10.1063/1.1585126 (3 pages) | Cited 4 times

Online Publication Date: 16 June 2003

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The growth of Si on thin ( ∼ 3 nm thick) CaF2/Si(111) films in the temperature range of 500–700 °C was investigated using ultrahigh-vacuum noncontact atomic force microscopy. At 500 °C, the morphology is dominated by small cluster-like shaped Si islands due to weak binding between Si and CaF2; with increasing growth temperatures these islands coexist with an increasing amount of triangular-shaped, flat Si islands. The formation of flattened triangular islands is attributed to an increased binding of Si to the CaF2 film at higher temperatures. The binding changes as a result of an interface reaction leading to the removal of fluorine atoms and the formation of Ca–Si bonds. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.Fx Diffusion; interface formation
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Atomic-layer-deposited WNxCy thin films as diffusion barrier for copper metallization

Soo-Hyun Kim, Su Suk Oh, Ki-Bum Kim, Dae-Hwan Kang, Wei-Min Li, Suvi Haukka, and Marko Tuominen

Appl. Phys. Lett. 82, 4486 (2003); http://dx.doi.org/10.1063/1.1585111 (3 pages) | Cited 13 times

Online Publication Date: 16 June 2003

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The properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethyl boron as source gases were characterized as a diffusion barrier for copper metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΩ cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of ∼ 48, 32, and 20 at. %, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1−x and β-W2N with an equiaxed microstructure. The barrier property of this ALD–WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700 °C for 30 min. © 2003 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
68.55.A- Nucleation and growth
85.40.Ls Metallization, contacts, interconnects; device isolation
68.35.Fx Diffusion; interface formation
61.66.Bi Elemental solids
61.66.Dk Alloys
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
68.37.Lp Transmission electron microscopy (TEM)
81.40.Gh Other heat and thermomechanical treatments

The characteristic carrier–Er interaction distance in Er-doped a-Si/SiO2 superlattices formed by ion sputtering

Ji-Hong Jhe, Jung H. Shin, Kyung Joong Kim, and Dae Won Moon

Appl. Phys. Lett. 82, 4489 (2003); http://dx.doi.org/10.1063/1.1586458 (3 pages) | Cited 42 times

Online Publication Date: 16 June 2003

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The characteristic interaction distance between Er3+ ions and carriers that excite them in Er-doped a-Si/SiO2 superlattices is investigated. Superlattice thin films consisting of 12 periods of a-Si/SiO2:Er/SiO2/SiO2:Er layers were deposited by ion sputtering and subsequent annealing at 950 °C. The dependence of the Er3+ photoluminescence intensity on the thickness of the Er-doped SiO2 layers is well-described by an exponentially decreasing Er-carrier interaction with a characteristic interaction distance of 0.5±0.1 nm. © 2003 American Institute of Physics.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.65.Cd Superlattices
78.55.-m Photoluminescence, properties and materials
61.72.Cc Kinetics of defect formation and annealing
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