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16 Apr 2001

Volume 78, Issue 16, pp. 2267-2404

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Photoluminescence and cathodoluminescence studies of stoichiometric and oxygen-deficient ZnO films

X. L. Wu, G. G. Siu, C. L. Fu, and H. C. Ong

Appl. Phys. Lett. 78, 2285 (2001); http://dx.doi.org/10.1063/1.1361288 (3 pages) | Cited 324 times

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Photoluminescence and cathodoluminescence (CL) spectra of stoichiometric and oxygen-deficient ZnO films grown on sapphire were examined. It was found that the intensities of the green and yellow emissions depend on the width of the free-carrier depletion region at the particle surface; the thinner the width, the larger the intensity. Experimental results and spectral analyses suggest that the mechanism responsible for the green (yellow) emission is the recombination of a delocalized electron close to the conduction band with a deeply trapped hole in the single ionized oxygen vacancy Vo+ (the single negatively charged interstitial oxygen ion Oi−) center in the particle. © 2001 American Institute of Physics.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
78.55.Et II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Gs II-VI semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.J- Point defects and defect clusters

Screw dislocations in GaN: The Ga-filled core model

John E. Northrup

Appl. Phys. Lett. 78, 2288 (2001); http://dx.doi.org/10.1063/1.1361274 (3 pages) | Cited 60 times

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First-principles total energy calculations performed for [0001] screw dislocations in GaN with ∣b∣ = c indicate that a model with a helical Ga-filled core is more stable than the hollow core model in Ga-rich conditions. This model gives rise to electronic states dispersed throughout the band gap. Such a dislocation is therefore expected to be a very strong center for nonradiative recombination and a pathway for current leakage. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.Lk Linear defects: dislocations, disclinations
71.15.Nc Total energy and cohesive energy calculations

Growth of aligned carbon nanotubes by biasing during growth

Y. Avigal and R. Kalish

Appl. Phys. Lett. 78, 2291 (2001); http://dx.doi.org/10.1063/1.1365409 (3 pages) | Cited 43 times

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Well aligned multiwalled carbon nanotube (CNT) growth was achieved by positively biasing the substrate during growth. Growth was performed in a flowing mixture of 7% CH4 in Ar onto Co covered Si held at 800 °C with and without the presence of an electric field. High resolution scanning electron microscopy shows that the tube alignment occurs only when a positive bias is applied to the substrate whereas no aligned growth occurs under a negative bias and no tube growth is observed, under the presently applied conditions, with no field. This finding may open up the possibility of realizing cold electron emitting devices based on CNTs with a large electric field enhancement. In particular, it may be possible to utilize the same gate which is needed to turn the device on also to obtain field assisted aligned carbon nanotube growth into the desired regions. Alternatively, due to the fact that no CNTs grow under the conditions of this experiment without bias, selected area biasing may permit selected area growth of vertically aligned carbon nanotubes, a process that may find many applications. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Roughness evolution in polyimide films during plasma etching

Navnit Agarwal, Shom Ponoth, Joel Plawsky, and P. D. Persans

Appl. Phys. Lett. 78, 2294 (2001); http://dx.doi.org/10.1063/1.1364507 (3 pages) | Cited 11 times

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We report an experimental study on the evolution of etch front roughness in fluorinated polyimide films in oxygen based plasmas. For standard low-pressure (40 mT) etching conditions, the root-mean-square roughness, w, of the polymer surface increases with the amount of material etched, d, as w = 0.0265(d−116)β with β = 1, independent of etch rate, rf power, and gas composition. The etched surfaces can be described by the statistics of self-affine surfaces with scaling exponent, α = 0.6±0.1 and lateral correlation length, ξ, of ∼ 0.3 μm. A dramatic reduction in roughness is observed under higher pressure etching conditions of 1000–2000 mT. © 2001 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
42.70.Jk Polymers and organics

Characterization of free-standing hydride vapor phase epitaxy GaN

J. Jasinski, W. Swider, Z. Liliental-Weber, P. Visconti, K. M. Jones, M. A. Reshchikov, F. Yun, H. Morkoç, S. S. Park, and K. Y. Lee

Appl. Phys. Lett. 78, 2297 (2001); http://dx.doi.org/10.1063/1.1359779 (3 pages) | Cited 30 times

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A free-standing GaN template grown by hydride vapor phase epitaxy has been characterized by transmission electron microscopy (TEM). The TEM investigation was augmented by x-ray diffraction, defect delineation etching process followed by imaging with atomic force microscopy and variable temperature photoluminescence. The density of dislocations near the N face was determined to be, in order, 3±1×107, 4±1×107, and about 1×107 cm−2 by cross-sectional TEM, plan-view TEM, and a defect revealing etch, respectively. The same methods on the Ga face revealed the defect concentration to be, in order, less than 1×107 cm−2 by plan-view TEM, less than 5×106 cm−2 by cross-sectional TEM, and 5×105 cm−2 by defect revealing hot H3PO4 acid, respectively. The full width at half maximum of the symmetric (0002) x-ray diffraction peak was 69 and 160 arc sec for the Ga and N faces, respectively. That for the asymmetric (10math4) peak was 103 and 140 arc sec for Ga and N faces, respectively. The donor bound exciton linewidth was about 1 meV each at 10 K, and a green band centered at about 2.44 eV was observed. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.65.Cf Surface cleaning, etching, patterning
71.35.Aa Frenkel excitons and self-trapped excitons

High-performance blue electroluminescent devices based on hydroxyphenyl-pyridine beryllium complex

Yu Liu, Jianhua Guo, Jing Feng, Huidong Zhang, Yanqin Li, and Yue Wang

Appl. Phys. Lett. 78, 2300 (2001); http://dx.doi.org/10.1063/1.1366338 (3 pages) | Cited 33 times

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Blue light organic electroluminescent (EL) devices with high-performance were fabricated by using a highly fluorescent material, bis[2-(2-hydroxyphenyl)-pyridine]beryllium (Bepp2). The double layer devices with a structure of [indium tin oxide/N, N′-di(α-naphthyl)-N-N′-diphenyl(1, 1′-biphenyl)-4, 4′-diamine (600 Å)/Bepp2 (500 Å)/LiF (10 Å)/Al (2000 Å)] exhibited a maximum luminance of 15 000 cd/m2 and a maximum electroluminescent efficiency of 3.43 lm/w (3.8 cd/A). © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices

Influence of the dipole interaction energy on clustering in InxGa1−xN alloys

E. J. Miller and E. T. Yu

Appl. Phys. Lett. 78, 2303 (2001); http://dx.doi.org/10.1063/1.1366651 (3 pages) | Cited 2 times

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The interactions of the polarization-induced dipole moments at each unit cell in InxGa1−xN alloys have been studied using analytical electrostatic dipole energy calculations to determine their potential influence on local material composition. Clustering of In atoms along the [0001] direction and anticlustering of In in the (0001) plane are shown to be energetically favorable. Comparisons of the dipole interaction energy to the strain energy and the energy associated with the decreased entropy of the ordered configurations show that the dipole interaction energy could have a substantial influence on local composition in InxGa1−xN alloys. © 2001 American Institute of Physics.
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64.75.-g Phase equilibria
81.05.Ea III-V semiconductors
81.30.Mh Solid-phase precipitation
61.66.Bi Elemental solids
61.66.Dk Alloys
65.40.G- Other thermodynamical quantities

Near-field photoreflectance spectroscopy of quantum well structures

Yong-Hoon Cho, Dai-Sik Kim, and Wonho Jhe

Appl. Phys. Lett. 78, 2306 (2001); http://dx.doi.org/10.1063/1.1353842 (3 pages)

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We present near-field photoreflectance (NPR) spectroscopic studies of GaAs/Al0.3Ga0.7As quantum well structures using a near-field scanning optical microscope with either an uncoated or a metal-coated tapered optical fiber probe. The NPR method provides advantages over conventional optical microscopic ones: (i) higher signal-to-noise ratio, (ii) lower temperature-sensitivity of the signal, and (iii) more information about higher electronic energy states. We also discuss the feasibility of a imaging with high resolution and contrast by using the NPR method. © 2001 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
68.37.Uv Near-field scanning microscopy and spectroscopy
78.40.Fy Semiconductors

Atomically resolved structure of InAs quantum dots

J. Márquez, L. Geelhaar, and K. Jacobi

Appl. Phys. Lett. 78, 2309 (2001); http://dx.doi.org/10.1063/1.1365101 (3 pages) | Cited 76 times

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InAs was grown by molecular-beam epitaxy onto GaAs(001) until quantum dots (QDs) formed. At this point, the growth was interrupted and the uncovered QDs were investigated in situ by scanning tunneling microscopy (STM). Atomically resolved STM images of the QDs revealed that four dominating bounding facets occur, whose Miller indices were identified to be {137}. The assignment of the facet orientation was based on experiments on planar high Miller index GaAs surfaces. In addition, the latter experiments indicated that {137} facets are thermodynamically stable only up to a certain size. This conclusion is assumed to explain the sharp size distribution of InAs QDs. © 2001 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

First principles study of the initial stages of SiC growth on Si(001)

Giancarlo Cicero and Alessandra Catellani

Appl. Phys. Lett. 78, 2312 (2001); http://dx.doi.org/10.1063/1.1366358 (3 pages) | Cited 6 times

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The initial stages of SiC growth on Si(001) are studied via ab initio molecular dynamics simulations at finite temperature. Several C coverages are considered, at various adsorption sites. At low T, C is adsorbed at the surface, with Si–C bond lengths close to that of bulk SiC. When increasing temperature, C adatoms are incorporated in the substrate subsurface layers, giving rise to the carbonization process. On the contrary, C dimers do not penetrate the substrate and remain stable even at the highest temperatures considered: our results point at radicals with single C atoms as efficient precursors for SiC growth. © 2001 American Institute of Physics.
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68.43.Mn Adsorption kinetics
81.05.Hd Other semiconductors

Hexagonal growth spirals on GaN grown by molecular-beam epitaxy: Kinetics versus thermodynamics

A. Parkhomovsky, A. M. Dabiran, B. Benjaminsson, and P. I. Cohen

Appl. Phys. Lett. 78, 2315 (2001); http://dx.doi.org/10.1063/1.1361278 (3 pages) | Cited 8 times

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GaN grown by molecular-beam epitaxy on Ga-polar GaN templates prepared by metal organic chemical vapor deposition shows a variety of morphologies that depend on defects and growth conditions. We measured the mean terrace widths of hexagonal growth spirals or hillocks versus ammonia and Ga fluxes and substrate temperature. The measurements were compared to a near equilibrium model of the growth. The results indicate that under excess Ga growth conditions, Ga-polar GaN(0001) has a mean step-edge energy of 0.27 eV/Å. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology

Natural oxides on air-exposed and chemically treated InGaP surfaces grown by metalorganic vapor phase epitaxy

Tamotsu Hashizume and Toshiya Saitoh

Appl. Phys. Lett. 78, 2318 (2001); http://dx.doi.org/10.1063/1.1366648 (3 pages) | Cited 5 times

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Chemical properties of natural oxides on air-exposed and chemically treated In0.49Ga0.51P surfaces grown by metalorganic vapor phase epitaxy were systematically investigated by x-ray photoelectron spectroscopy. An air-exposed sample exhibited a highly In-rich surface which included a large amount of natural oxides. From the valence-band spectra and energy separations between core levels, it was found that the InPO4-like chemical phase was dominant in natural oxides of air-exposed InGaP surfaces. Chemical surface treatments in HCl and HF solutions were effective in reducing natural oxide and in recovering the surface stoichiometry. © 2001 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Ea III-V semiconductors
68.55.Nq Composition and phase identification
79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
81.65.Cf Surface cleaning, etching, patterning
68.35.Dv Composition, segregation; defects and impurities

Retardation of boron diffusion in silicon by defect engineering

Lin Shao, Xinming Lu, Xuemei Wang, Irene Rusakova, Jiarui Liu, and Wei-Kan Chu

Appl. Phys. Lett. 78, 2321 (2001); http://dx.doi.org/10.1063/1.1361280 (3 pages) | Cited 25 times

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By judiciously placing vacancy and interstitial defects at different depths, we are able to enhance or retard boron diffusion. This opens up a new approach for the formation of shallow P+n junction in silicon. After preimplantation with 50 or 500 keV Si+ ions to produce a surface vacancy-rich region, we studied the diffusion of deposited B on predamaged samples with annealing between 900 and 1010 °C. Boron diffusion retardation was observed in both implantation conditions after low temperature annealing with enhancement occurring in a 50 keV implanted sample at high temperature. Choosing high energy implantation to separate vacancies and interstitials can reduce the boron diffusion significantly. Such suppression became more obvious with higher implant doses. A junction less than 10 nm deep (at 1×1017 cm−3 according to carrier concentration profiles) can be formed. © 2001 American Institute of Physics.
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61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.J- Point defects and defect clusters
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Cy Elemental semiconductors

Phase field microelasticity theory and modeling of multiple dislocation dynamics

Y. U. Wang, Y. M. Jin, A. M. Cuitiño, and A. G. Khachaturyan

Appl. Phys. Lett. 78, 2324 (2001); http://dx.doi.org/10.1063/1.1366370 (3 pages) | Cited 35 times

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The phase field theory and model of a multidislocation dynamics in an elastically anisotropic crystal under applied stress is developed. The proposed three-dimensional (3D) model is a particular case of our phase field microelasticity model of the stress-induced martensitic transformations. A spontaneous self-organization of dislocations in the evolving ensemble, which involves multiplication/annihilation and movement of dislocations controlled by their elastic interaction, is described by the Ginzburg–Landau kinetic equation. Examples of 3D computer simulation of dislocation dynamics are considered. © 2001 American Institute of Physics.
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61.72.Bb Theories and models of crystal defects
61.72.Lk Linear defects: dislocations, disclinations
66.30.Lw Diffusion of other defects
07.05.Tp Computer modeling and simulation
62.20.D- Elasticity
46.25.Cc Theoretical studies

Midinfrared absorption and photocurrent spectroscopy of InAs/GaAs self-assembled quantum dots

S. Sauvage, P. Boucaud, T. Brunhes, V. Immer, E. Finkman, and J.-M. Gérard

Appl. Phys. Lett. 78, 2327 (2001); http://dx.doi.org/10.1063/1.1365411 (3 pages) | Cited 35 times

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We report on a comparison between the midinfrared absorption and the photocurrent response of n-doped InAs/GaAs self-assembled quantum dots. The absorption, resonant at 160 meV, is polarized along the z growth axis of the dots. The photocurrent is dominated by a z-polarized resonance around 220 meV (5.6 μm wavelength). A weaker component of the photocurrent is observed for an in-plane polarized excitation. The photoresponse can be measured for a 0 V applied bias. The photoresponsivity is investigated as a function of the applied bias. The responsivity and the dark current exhibit an asymmetric profile versus the external bias. This asymmetry is correlated to the structural asymmetry of the quantum dot layers. © 2001 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
81.05.Ea III-V semiconductors
73.63.Kv Quantum dots
81.07.Ta Quantum dots
78.30.Fs III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
73.21.La Quantum dots
78.67.Hc Quantum dots
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