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24 Jan 2000

Volume 76, Issue 4, pp. 397-519

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Investigations on the Stranski–Krastanow growth of CdSe quantum dots

D. Schikora, S. Schwedhelm, D. J. As, K. Lischka, D. Litvinov, A. Rosenauer, D. Gerthsen, M. Strassburg, A. Hoffmann, and D. Bimberg

Appl. Phys. Lett. 76, 418 (2000); http://dx.doi.org/10.1063/1.125773 (3 pages) | Cited 50 times

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We have investigated the growth kinetics of the self-assembled formation of coherently strained CdSe islands. We have found that two distinctly different types of islands are formed in succession. Analyzing the density distribution function of the two dominating size classes of islands, we show that islands of an average diameter of about 16 nm (type B islands) are correlated with a phase transition via a Stranski–Krastanow growth process. The other islands with a diameter of less than 10 nm (type A islands) is formed during the growth of the first 2 ML. At a coverage of about 3.1 ML CdSe stacking faults appear, indicating the beginning of the plastic relaxation of the quantum dot structure. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Desorption of positive ions from ionic crystals accompanying 248 nm laser irradiation

C. Bandis, S. C. Langford, and J. T. Dickinson

Appl. Phys. Lett. 76, 421 (2000); http://dx.doi.org/10.1063/1.125774 (3 pages) | Cited 18 times

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We present a study of the energy distributions of positive ions (Na+, Li+, Ca+, and Mg+) photodesorbed from cleaved NaCl, LiF, MgO, NaNO3, and CaCO3 surfaces during 248 nm excimer laser irradiation at fluences well below the damage thresholds. The observed ion energies are significantly higher than those predicted by already existing models that allow ion rearrangement and relaxation during the electrostatic ion repulsion by the nearby photoionized sites. In contrast to what one would expect, we find that treating the ions as fixed charges and neglecting any ion rearrangement during the emission of the adions describes best the experimentally observed ion energies from all five ionic crystals. © 2000 American Institute of Physics.
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79.20.La Photon- and electron-stimulated desorption
79.20.Ds Laser-beam impact phenomena
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Formation of Ti3+ in sapphire by co-implantation of Ti and O ions

L. D. Morpeth and J. C. McCallum

Appl. Phys. Lett. 76, 424 (2000); http://dx.doi.org/10.1063/1.125775 (3 pages) | Cited 4 times

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We have demonstrated that co-implantation of Ti and O ions into c-axis oriented α-Al2O3 substrates followed by thermal annealing can substantially increase the fraction of Ti ions present in the optically active 3+ oxidation state. Evidence for the presence of Ti3+ is given by the observation of strong luminescence over the wavelength range ∼ 600–900 nm under Ar laser excitation and by the presence of the characteristic absorption band at ∼ 450–550 nm. We have studied the luminescence intensity as a function of implantation and annealing parameters and have found that there is a strong dependence on the ratio of implanted Ti and O and on the annealing temperature. © 2000 American Institute of Physics.
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61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
71.55.Ht Other nonmetals
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
78.55.Hx Other solid inorganic materials

A plasma process for ultrafast deposition of SiGe graded buffer layers

C. Rosenblad, H. von Känel, M. Kummer, A. Dommann, and E. Müller

Appl. Phys. Lett. 76, 427 (2000); http://dx.doi.org/10.1063/1.125776 (3 pages) | Cited 34 times

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Low energy plasma enhanced chemical vapor deposition (LEPECVD) has been applied to the synthesis of Si-modulation doped field effect transistor structures, comprising a SiGe relaxed buffer layer and a modulation doped strained Si channel. A growth rate of at least 5 nm/s for the relaxed SiGe buffer layer is well above that obtainable by any other technique. Due to the low ion energies involved in LEPECVD, ion damage is absent, despite a huge plasma density. The structural quality of the LEPECVD grown SiGe buffer layers is comparable to that of state-of-the-art material. The electronic properties of the material were evaluated by growing modulation doped Si quantum wells on the buffer layers. We obtain a low temperature (2 K) Hall mobility of μH = 2.5×104 cm2/Vs for the electrons in the Si channel at an electron sheet density of ns = 8.6×1011 cm−2. © 2000 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Hd Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Thermally induced stress relaxation and densification of spin-on-glass thin films

C. K. Chiang, W. E. Wallace, G. W. Lynn, D. Feiler, and W. Xia

Appl. Phys. Lett. 76, 430 (2000); http://dx.doi.org/10.1063/1.125777 (3 pages) | Cited 8 times

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The stress–temperature relationship of silica spin-on-glass thin films on silicon wafers was studied. Upon heating, the stress–temperature curves showed a dramatically increasing slope when the temperature of the film was greater than 340 °C. At 450 °C, a significant, irreversible change in the stress of the film was observed. This change in stress was correlated with an increase in film electron density and a decrease in film thickness. The observed thermally activated stress–relaxation behavior was interpreted in terms of reflow of the glassy hydrogen–silsesquioxane-based material. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Enhancement of electromechanical coupling coefficient by proton exchange in Z-cut LiNbO3

D. Čiplys, R. Rimeika, Yu. N. Korkishko, and V. A. Fedorov

Appl. Phys. Lett. 76, 433 (2000); http://dx.doi.org/10.1063/1.125778 (3 pages) | Cited 2 times

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The electromechanical coupling coefficient K for surface acoustic waves (SAWs) in proton-exchanged Z-cut X-propagation lithium niobate has been experimentally investigated by the method of evaporating a thin metal film and measuring in situ the SAW attenuation. The enhancement in K2 value by as much as two times caused by the proton exchange has been observed. It is attributed to the redistribution of electric potential of the acoustic wave due to formation of a HxLi1−xNbO3 layer at the surface. The change of electromechanical coupling coefficient in samples fabricated under different conditions depends on the acoustic wavelength–layer thickness product kd. The K2 value attains a maximum of about 0.8×10−2 at kd ≈ 0.4, whereas it is equal to 0.46×10−2 in nonexchanged lithium niobate. The increase in electromechanical coupling coefficient can be applied for enhancement of the SAW interdigital transducer efficiency. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
43.35.Pt Surface waves in solids and liquids
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.35.Gy Mechanical properties; surface strains

Structure and stability of ultrathin zirconium oxide layers on Si(001)

M. Copel, M. Gribelyuk, and E. Gusev

Appl. Phys. Lett. 76, 436 (2000); http://dx.doi.org/10.1063/1.125779 (3 pages) | Cited 355 times

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We have examined the structure of ultrathin ZrO2 layers on Si(001) using medium energy ion scattering and cross-sectional transmission electron microscopy. Films can be deposited on SiO2 layers with highly abrupt interfaces by atomic layer deposition. On HF stripped Si(001), nucleation was inhibited, resulting in poorer film morphology. ZrO2 showed remarkable stability against silicate formation, with no intermixing even after high temperature oxidation. The oxide is vulnerable to high temperature vacuum annealing, with silicidation occurring at temperatures above 900 °C. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Dv Thermal stability; thermal effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
68.35.Ct Interface structure and roughness

Two-photon absorption study of GaN

Chi-Kuang Sun, Jian-Chin Liang, Jiun-Cheng Wang, Fu-Jen Kao, Stacia Keller, Michael P. Mack, Umesh Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 76, 439 (2000); http://dx.doi.org/10.1063/1.125780 (3 pages) | Cited 40 times

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Two-photon absorption coefficients of GaN for below band gap ultraviolet wavelength and midgap infrared wavelength were measured by using femtosecond pulsewidth autocorrelation and Z-scan techniques. Large two-photon absorption coefficients were obtained. Taking advantage of the large two-photon absorption, we have demonstrated two-photon confocal imaging of a GaN thin film. Direct correlation was found between the yellow luminescence and suppression of bandedge luminescence. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Self-organized propagation of dislocations in GaN films during epitaxial lateral overgrowth

Akira Sakai, Haruo Sunakawa, Akitaka Kimura, and Akira Usui

Appl. Phys. Lett. 76, 442 (2000); http://dx.doi.org/10.1063/1.125781 (3 pages) | Cited 30 times

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Dislocation propagation and defect evolution in GaN films formed by epitaxial lateral overgrowth (ELO) are examined by transmission electron microscopy. A novel effect that induces self-organized propagation of preexisting dislocations in ELO films is evaluated. This propagation forms dislocations into bundle structures along the stripes of masks used for ELO. The dislocation bundling gives rise to crystallographic tilting in the overgrown region on the mask and leads to a total reduction of threading dislocation density in the film. © 2000 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.Lw Diffusion of other defects
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