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27 May 2002

Volume 80, Issue 21, pp. 3883-4065

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Self-organized growth of three-dimensional quantum-dot superlattices

P. Liu, Y. W. Zhang, and C. Lu

Appl. Phys. Lett. 80, 3910 (2002); http://dx.doi.org/10.1063/1.1481541 (3 pages) | Cited 9 times

Online Publication Date: 20 May 2002

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The self-organization of three-dimensional quantum-dot superlattices that spontaneously form during heteroepitaxial growth is investigated by using a three-dimensional kinetic model. The model predictions show that the multilayer arrays of quantum dots can be fully or partially aligned vertically, or completely misaligned with respect to the buried islands, depending on the thickness of the spacer layer and the growth interruption time. In particular, there is a growth window in which a nearly uniform and regular array of dots is arranged in a squared lattice with an alternating stacking sequence; namely, the A–B–A–B stacking sequence. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
81.16.Dn Self-assembly
68.65.Hb Quantum dots (patterned in quantum wells)
68.65.Cd Superlattices

Strain and composition distributions in wurtzite InGaN/GaN layers extracted from x-ray reciprocal space mapping

S. Pereira, M. R. Correia, E. Pereira, K. P. O’Donnell, E. Alves, A. D. Sequeira, N. Franco, I. M. Watson, and C. J. Deatcher

Appl. Phys. Lett. 80, 3913 (2002); http://dx.doi.org/10.1063/1.1481786 (3 pages) | Cited 61 times

Online Publication Date: 20 May 2002

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Strain and composition distributions within wurtzite InGaN/GaN layers are investigated by high-resolution reciprocal space mapping (RSM). We illustrate the potential of RSM to detect composition and strain gradients independently. This information is extracted from the elongation of broadened reciprocal lattice points (RLP) in asymmetric x-ray reflections. Three InxGa1−xN/GaN (nominal x = 0.25) samples with layer thickness of 60, 120, and 240 nm, were grown in a commercial metal-organic chemical vapor deposition reactor. The RSMs around the (105) reflection show that the strain profile is nonuniform over depth in InGaN. The directions of “pure” strain relaxation in the reciprocal space, for a given In content (isocomposition lines), are calculated based on elastic theory. Comparison between these directions and measured distributions of the RLP shows that the relaxation process does not follow a specific isocomposition line. The In mole fraction (x) increases as the films relax. At the start of growth all the films have x ∼ 0.2 and are coherent to GaN. As they relax, x progressively increases towards the nominal value (0.25). Compositional gradients along the growth direction extracted from the RSM analysis are confirmed by complementary Rutherford backscattering measurements. © 2002 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effects of H2 impregnation on excimer-laser-induced oxygen-deficient center formation in synthetic SiO2 glass

Yoshiaki Ikuta, Koichi Kajihara, Masahiro Hirano, Shinya Kikugawa, and Hideo Hosono

Appl. Phys. Lett. 80, 3916 (2002); http://dx.doi.org/10.1063/1.1481789 (3 pages) | Cited 10 times

Online Publication Date: 20 May 2002

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We examined the effect of H2 impregnation on defect formation upon F2 laser (7.9 eV) and ArF excimer laser (6.4 eV) irradiation. It was revealed that H2 impregnation enhanced the formation of oxygen-deficient center (Si–Si bond) as well as suppressed the formation of E′ center and nonbridging oxygen hole center. A Si–Si bond gives an intense absorption band peaking at 7.6 eV, which contributes the absorption at the wavelength of F2 laser light. These results indicate that H2-free SiO2 glass, which is clearly inappropriate for KrF and ArF excimer laser optics, is more suitable for F2 laser optics than H2-impregnated glass. © 2002 American Institute of Physics.
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61.82.Ms Insulators
61.43.Fs Glasses
42.88.+h Environmental and radiation effects on optical elements, devices, and systems
78.40.Pg Disordered solids
78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
85.40.Hp Lithography, masks and pattern transfer

Spectrally modified chirped pulse generation of sustained shock waves

S. D. McGrane, D. S. Moore, D. J. Funk, and R. L. Rabie

Appl. Phys. Lett. 80, 3919 (2002); http://dx.doi.org/10.1063/1.1481986 (3 pages) | Cited 18 times

Online Publication Date: 20 May 2002

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A method is described for generating shock waves with 10–20 ps risetime followed by >200 ps constant pressure, using spectrally modified (clipped) chirped laser pulses. The degree of spectral clipping alters the chirped pulse temporal intensity profile and thereby the time-dependent pressure (tunable via pulse energy) generated in bare and nitrocellulose-coated Al thin films. The method is implementable in common chirped amplified lasers, and allows synchronous probing with a <200 fs pulse. © 2002 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
43.40.Jc Shock and shock reduction and absorption
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
42.60.Fc Modulation, tuning, and mode locking

Epitaxial growth and electronic structure of LaTiOx films

A. Ohtomo, D. A. Muller, J. L. Grazul, and H. Y. Hwang

Appl. Phys. Lett. 80, 3922 (2002); http://dx.doi.org/10.1063/1.1481767 (3 pages) | Cited 42 times

Online Publication Date: 20 May 2002

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LaTiOx films have been grown on (001) perovskite oxide substrates by pulsed-laser deposition. Both single-phase perovskite LaTiO3 and layered La2Ti2O7 films could be stabilized by varying the oxygen partial pressure and substrate temperature during growth. We have obtained a crystallographic and electronic phase diagram for LaTiOx films, demonstrating the ability to vary the titanium valence from 3+ to 4+ in thermodynamically unfavorable growth conditions by utilizing interface energies. © 2002 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
71.20.Ps Other inorganic compounds
79.20.Uv Electron energy loss spectroscopy
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.37.Lp Transmission electron microscopy (TEM)

Ultrafast x-ray pulse generation by focusing femtosecond infrared laser pulses onto aqueous solutions of alkali metal chloride

Koji Hatanaka, Toshifumi Miura, and Hiroshi Fukumura

Appl. Phys. Lett. 80, 3925 (2002); http://dx.doi.org/10.1063/1.1482135 (3 pages) | Cited 14 times

Online Publication Date: 20 May 2002

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X-ray pulses were generated by focusing femtosecond infrared laser pulses (775 nm, 130 fs, 0.58 mJ/pulse) onto an alkali metal (Cs or Rb) chloride aqueous solution jet. The mechanism of x-ray pulse generation was studied by measuring x-ray emission spectra and transmitted laser pulse spectra. Addition of CsCl to distilled water was found to enhance markedly x-ray intensity and x-ray cutoff energy. The frequency-up-shift observed in transmitted laser pulses was larger in CsCl solution than in distilled water. The results suggested that a high-density plasma-like medium was produced in CsCl solution due to secondary electrons. © 2002 American Institute of Physics.
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78.70.En X-ray emission spectra and fluorescence
78.45.+h Stimulated emission
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Longitudinal Excitons in GaN

D. C. Reynolds, B. Jogai, and T. C. Collins

Appl. Phys. Lett. 80, 3928 (2002); http://dx.doi.org/10.1063/1.1471372 (3 pages) | Cited 5 times

Online Publication Date: 20 May 2002

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Many of the previous investigations of longitudinal excitons have involved reflection and absorption measurements rather than emission. In these measurements it is more difficult to resolve the longitudinal exciton from the Γ5 and Γ6 free excitons in wurtzite material. The longitudinal excitons have energies and oscillator strengths that depend on the direction of propagation and they are not observable along the principal axis of the crystal. In the wurtzite structure, such as GaN, the Γ5 exciton is the pure transverse mode, whereas the longitudinal is a mixed mode going from pure longitudinal, for the propogation direction K perpendicular to C, to pure transverse for K parallel to C. If more than one orientation is present in the sample, it is clear that more than one longitudinal exciton may be seen since it is a mixed mode. In the current experiment we observe more than one mode, which we associate with more than one crystal orientation. This may result from the columnar growth often observed in GaN. © 2002 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors

Strain-induced surface segregation in In0.5Ga0.5As/GaAs heteroepitaxy

Akihiro Ohtake, Masashi Ozeki, Masami Terauchi, Futami Sato, and Michiyoshi Tanaka

Appl. Phys. Lett. 80, 3931 (2002); http://dx.doi.org/10.1063/1.1482792 (3 pages) | Cited 2 times

Online Publication Date: 20 May 2002

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Surface segregation and strain relaxation processes in layer-by-layer growing InxGa1−xAs films on the GaAs(001) and GaAs(111)A substrates have been studied. While the lattice strain is almost relaxed by introducing misfit dislocations on the (111)A substrate, the in-plane lattice constant of the growing film on the (001) substrate hardly changes throughout the growth. We found that a significant amount of In atoms is segregated to the growing surface on the (001) substrate, which is induced by the lattice strain at the coherent (001) interface. © 2002 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Ea III-V semiconductors

Gallium vacancy and the residual acceptor in undoped GaSb studied by positron lifetime spectroscopy and photoluminescence

C. C. Ling, W. K. Mui, C. H. Lam, C. D. Beling, S. Fung, M. K. Lui, K. W. Cheah, K. F. Li, Y. W. Zhao, and M. Gong

Appl. Phys. Lett. 80, 3934 (2002); http://dx.doi.org/10.1063/1.1482419 (3 pages) | Cited 9 times

Online Publication Date: 20 May 2002

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Positron lifetime, photoluminescence (PL), and Hall measurements were performed to study undoped p-type gallium antimonide materials. A 314 ps positron lifetime component was attributed to Ga vacancy (VGa) related defect. Isochronal annealing studies showed at 300 °C annealing, the 314 ps positron lifetime component and the two observed PL signals (777 and 797 meV) disappeared, which gave clear and strong evidence for their correlation. However, the hole concentration ( ∼ 2×1017 cm−3) was observed to be independent of the annealing temperature. Although the residual acceptor is generally related to the VGa defect, at least for cases with annealing temperatures above 300 °C, VGa is not the acceptor responsible for the p-type conduction. © 2002 American Institute of Physics.
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78.70.Bj Positron annihilation
78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

High-density and size-controlled GaN self-assembled quantum dots grown by metalorganic chemical vapor deposition

M. Miyamura, K. Tachibana, and Y. Arakawa

Appl. Phys. Lett. 80, 3937 (2002); http://dx.doi.org/10.1063/1.1482416 (3 pages) | Cited 50 times

Online Publication Date: 20 May 2002

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GaN self-assembled quantum dots (QDs) with high quality and high density have been grown by low-pressure metalorganic chemical vapor deposition under very low V/III ratios. In depositing over a critical thickness of four monolayer GaN, we observed a transition from two-dimensional to three-dimensional growth mode. The density of the QDs could be changed between 109 and 1010 cm−2. The typical diameter and height of the QDs were 20 and 2 nm, respectively. The size of the QDs was controlled to a considerable extent by changing the growth temperature and V/III ratio. Moreover, we observed two photoluminescence peaks from both the QDs and the wetting layer at room temperature. This result clearly demonstrates that the GaN QDs were formed with the Stranski–Krastanow growth mode. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.16.Dn Self-assembly
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Nanoporous-carbon films for microsensor preconcentrators

M. P. Siegal, D. L. Overmyer, R. J. Kottenstette, D. R. Tallant, and W. G. Yelton

Appl. Phys. Lett. 80, 3940 (2002); http://dx.doi.org/10.1063/1.1480469 (3 pages) | Cited 9 times

Online Publication Date: 20 May 2002

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Nanoporous-carbon (NPC) films are grown using physical processes such as low-power pulsed-laser deposition with attenuation of the ablated carbon species kinetic energy attained by using an inert background gas. With room-temperature growth and negligible residual stress, NPC can coat nearly any substrate to any desired thickness. Control of the deposition energetics yields precise morphology, density, and hence, porosity, with no discernable variation in chemical bonding. We produce NPC films 8 μm thick with density <0.2 g/cm3. The well-controlled porosity, i.e., available surface area, is demonstrated by using films with different thicknesses as a preconcentrator for a nerve-gas simulant. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
78.30.Na Fullerenes and related materials
78.66.Tr Fullerenes and related materials

Time-resolved photoluminescence of quaternary AlInGaN-based multiple quantum wells

Mee-Yi Ryu, C. Q. Chen, E. Kuokstis, J. W. Yang, G. Simin, M. Asif Khan, G. G. Sim, and P. W. Yu

Appl. Phys. Lett. 80, 3943 (2002); http://dx.doi.org/10.1063/1.1482415 (3 pages) | Cited 9 times

Online Publication Date: 20 May 2002

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Time-resolved photoluminescence (PL) dynamics has been studied in AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by a pulsed metalorganic chemical vapor deposition (PMOCVD) procedure. The PL decay kinetics was found to be sensitive to the emission energy and temperature. The PL decay time increases with decreasing emission energy, which is a characteristic of localized carrier/exciton recombination due to alloy fluctuations. Its temperature dependence shows radiative recombination to be the dominant process at low temperatures, indicating a high quality of PMOCVD grown quaternary AlInGaN MQWs and establishing them as promising structures for the active region of deep ultraviolet light emitting diodes. © 2002 American Institute of Physics.
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78.67.De Quantum wells
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.05.Ea III-V semiconductors
73.21.Fg Quantum wells
81.07.St Quantum wells
73.21.Cd Superlattices
71.35.-y Excitons and related phenomena

Piezoelectric in situ transmission electron microscopy technique for direct observations of fatigue damage accumulation in constrained metallic thin films

X. Tan, T. Du, and J. K. Shang

Appl. Phys. Lett. 80, 3946 (2002); http://dx.doi.org/10.1063/1.1481768 (3 pages) | Cited 6 times

Online Publication Date: 20 May 2002

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A piezoelectric in situ transmission electron microscopy (TEM) technique has been developed to observe the damage mechanism in constrained metallic thin films under cyclic loading. The technique was based on the piezoelectric actuation of a multilayered structure in which a metallic thin film was sandwiched between a piezoelectric actuator and a silicon substrate. An alternating electric field with a static offset was applied on the piezoelectric actuator to drive the crack growth in the thin metallic layer while the sample was imaged in TEM. The technique was demonstrated on solder thin films where cavitation was found to be the dominant fatigue damage mechanism. © 2002 American Institute of Physics.
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81.70.Bt Mechanical testing, impact tests, static and dynamic loads
68.60.Bs Mechanical and acoustical properties
68.37.Lp Transmission electron microscopy (TEM)
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Dislocation behavior in InGaN/GaN multi-quantum-well structure grown by metalorganic chemical vapor deposition

Y.-W. Kim, E.-K. Suh, and H. J. Lee

Appl. Phys. Lett. 80, 3949 (2002); http://dx.doi.org/10.1063/1.1481983 (3 pages) | Cited 5 times

Online Publication Date: 20 May 2002

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Propagation characteristics of dislocations were investigated in InGaN/GaN multi-quantum-well structures grown by metalorganic chemical vapor deposition. Threading dislocations with Burgers vector of b = 〈mathmath20〉, emerged from the GaN buffer region, change their glide plane from normal to parallel to the growth plane when they meet InGaN wells. Dislocations gliding on the growth planes were pinned by quantum dots leaving two possible ways of propagation, changing their glide plane back to normal to the growth plane, {10math0}, or extending loop shape pinned both ends by the quantum dots. Indium-rich quantum dots were formed on the InGaN quantum-well layers with size of 30±25 nm in diameter. It was estimated that the critical size of quantum dots to pin the dislocations is 30 nm. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
81.07.St Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.37.Lp Transmission electron microscopy (TEM)
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