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1 Aug 2000

Volume 88, Issue 3, pp. 1201-1704

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Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes

Leonid V. Zhigilei and Barbara J. Garrison

J. Appl. Phys. 88, 1281 (2000); http://dx.doi.org/10.1063/1.373816 (18 pages) | Cited 130 times

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The results of large-scale molecular dynamics simulations demonstrate that the mechanisms responsible for material ejection as well as most of the parameters of the ejection process have a strong dependence on the rate of the laser energy deposition. For longer laser pulses, in the regime of thermal confinement, a phase explosion of the overheated material is responsible for the collective material ejection at laser fluences above the ablation threshold. This phase explosion leads to a homogeneous decomposition of the expanding plume into a mixture of liquid droplets and gas phase molecules. The decomposition proceeds through the formation of a transient structure of interconnected liquid clusters and individual molecules and leads to the fast cooling of the ejected plume. For shorter laser pulses, in the regime of stress confinement, a lower threshold fluence for the onset of ablation is observed and attributed to photomechanical effects driven by the relaxation of the laser-induced pressure. Larger and more numerous clusters with higher ejection velocities are produced in the regime of stress confinement as compared to the regime of thermal confinement. For monomer molecules, the ejection in the stress confinement regime results in broader velocity distributions in the direction normal to the irradiated surface, higher maximum velocities, and stronger forward peaking of the angular distributions. The acoustic waves propagating from the absorption region are much stronger in the regime of stress confinement and the wave profiles can be related to the ejection mechanisms. © 2000 American Institute of Physics.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
62.65.+k Acoustical properties of solids

Electrical behavior of ultra-low energy implanted boron in silicon

V. Privitera, E. Schroer, F. Priolo, E. Napolitani, and A. Carnera

J. Appl. Phys. 88, 1299 (2000); http://dx.doi.org/10.1063/1.373817 (8 pages) | Cited 24 times

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In this paper an extensive characterization of the electrical activation of ultra-low energy implanted boron in silicon is reported. The Spreading Resistance Profiling technique has been used, in a suitable configuration, for measuring doped layers shallower than 100 nm, in order to extract the carrier concentration profiles. The dependence on the implant energy, dose, and annealing temperature allowed us to gain more insight into the mechanisms responsible for the electrical activation at implant energies below 1 keV. By measuring the electrical activation as a function of time for several annealing temperatures, the thermal activation energy for the electrical activation of the dopant was achieved. It slightly depends on the implant dose and it is in the range of 2–3 eV. In particular, for an implant dose of 1×1014/cm2 it is 2.0 eV, close therefore to the 1.7 eV activation energy found [Napolitani et al., Appl. Phys. Lett. 75, 1869 (1999)] for the enhanced diffusion of ultra-low energy implanted boron. The best conditions to maximize electrical activation, while minimizing diffusion, are identified and junction depths of ∼50 nm with sheet resistance below 500 Ω reported. These data are reported and their implication for the fabrication of future generation devices is discussed. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
66.30.J- Diffusion of impurities
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors

Investigation of threading dislocation blocking in strained-layer InGaAs/GaAs heterostructures using scanning cathodoluminescence microscopy

J. J. Russell, J. Zou, A. R. Moon, and D. J. H. Cockayne

J. Appl. Phys. 88, 1307 (2000); http://dx.doi.org/10.1063/1.373818 (5 pages) | Cited 1 time

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Threading dislocation glide relieves strain in strained-layer heterostructures by increasing the total length of interface misfit dislocations. The blocking theory proposed by Freund [J. Appl. Phys. 68, 2073 (1990)] predicts the thickness above which gliding threading dislocations are able to overcome the resistance force produced by existing orthogonal misfit dislocations. A set of wedge-shaped samples of InxGa1−xAs/GaAs (x=0.04) strained-layer heterostructures was grown using molecular-beam epitaxy in order to test the theory of dislocation blocking over a range of thicknesses within one sample. Scanning cathodoluminescence microscopy techniques were used to image the misfit dislocations. The cathodoluminescence results confirm the model proposed by Freund. © 2000 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology

Transmission electron microscopy characterization of secondary defects created by MeV Si, Ge, and Sn implantation in silicon

J. Wong-Leung, S. Fatima, C. Jagadish, J. D. Fitz Gerald, C. T. Chou, J. Zou, and D. J. H. Cockayne

J. Appl. Phys. 88, 1312 (2000); http://dx.doi.org/10.1063/1.373819 (7 pages) | Cited 5 times

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Extended defects created in Si by ion implantation to doses below the amorphization threshold have been studied after annealing at 800 °C for 15 min. The implant species were the group IV elements Si, Ge, and Sn, and structural defects created by similar damage distribution were compared. The mass of the implanted ion influences the type of defect observed. For all three implant species, rod-like {311} planar defects were observed. Additionally, in Ge and Sn implanted samples, small {111} interstitial faulted dislocation loops were observed. © 2000 American Institute of Physics.
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61.72.uf Ge and Si
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.72.Nn Stacking faults and other planar or extended defects
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Emission channeling studies of Pr in GaN

U. Wahl, A. Vantomme, G. Langouche, J.P. Araújo, L. Peralta, and J. G. Correia

J. Appl. Phys. 88, 1319 (2000); http://dx.doi.org/10.1063/1.373820 (6 pages) | Cited 29 times

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We report on the lattice location of Pr in thin film, single-crystalline hexagonal GaN using the emission channeling technique. The angular distribution of β− particles emitted by the radioactive isotope 143Pr was monitored by a position-sensitive electron detector following 60 keV room temperature implantation of the precursor isotope 143Cs at a dose of 1×1013 cm−2 and annealing up to 900 °C. Our experiments provide direct evidence that Pr is thermally stable at substitutional Ga sites. © 2000 American Institute of Physics.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)
61.72.S- Impurities in crystals

Characterization of defects in (ZnMg)Se compounds by positron annihilation and photoluminescence

F. Plazaola, K. Saarinen, L. Dobrzynski, H. Reniewicz, F. Firszt, J. Szatkowski, H. Meczynska, S. Legowski, and S. Chabik

J. Appl. Phys. 88, 1325 (2000); http://dx.doi.org/10.1063/1.373821 (8 pages) | Cited 12 times

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Defect characterization of as-grown Zn1−xMgxSe mixed crystals (0⩽x<0.6) and the effect of Zn vapor annealing has been studied by positron lifetime and photoluminescence measurements. We obtain both experimental and theoretical evidence that the bulk lifetime of free positrons increases linearly with Mg alloying. The average positron lifetime increases with temperature indicating that both vacancies and negative ions trap positrons. The decompositions of the lifetime spectra show that the vacancy has the characteristic positron lifetime of 325 ps. The comparison with theoretical calculations indicate that the lifetime 325 ps corresponds either to divacancies relaxed inwards or to monovacancies strongly relaxed outwards. We consider the latter identification more likely and attribute the positron lifetime 325 ps to Zn vacancy or a complex involving VZn. The vacancy concentration is almost independent of Mg content above x=0.2 but decreases strongly at x=0.56. The Zn vapor annealing decreases the concentration of Zn vacancies. The intensity of the green photoluminescence correlates with the concentration of VZn both as a function of Mg alloying and Zn vapor annealing. We thus conclude that the electron levels of the Zn vacancy are involved in the optical transition leading to the green photoluminescence. © 2000 American Institute of Physics.
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78.70.Bj Positron annihilation
78.55.Hx Other solid inorganic materials
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
71.55.Ht Other nonmetals

Electron beam stimulated formation of CdS nanoparticles within calixarene Langmuir–Blodgett films

A. V. Nabok, A. K. Ray, and A. K. Hassan

J. Appl. Phys. 88, 1333 (2000); http://dx.doi.org/10.1063/1.373877 (6 pages) | Cited 9 times

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Two possible types of cadmium sulphide (CdS) nanostructures can be formed within Langmuir–Blodgett (LB) films of calixarene Cd salt as a result of exposure to H2S gas: nanoclusters with the size of about 1.5 nm or two-dimensional planes with the thickness of about 1.7 nm. Transmission electron microscopy and electron diffraction studies on calixarene/CdS LB films show that CdS particles are not present in the fresh samples at the beginning, but they are gradually formed under exposure to a high energy electron beam. A blueshift of the first exciton absorption band and an increase of the extinction coefficient, caused by exposure to H2S gas, were found with UV-visible optical spectroscopy and surface plasmon resonance, respectively. © 2000 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
78.66.Hf II-VI semiconductors
61.46.-w Structure of nanoscale materials
73.22.-f Electronic structure of nanoscale materials and related systems
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.18.-g Langmuir-Blodgett films on liquids
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.40.Fy Semiconductors

Self-trapped exciton luminescence induced in alpha quartz by swift heavy ion irradiations

J. M. Costantini, F. Brisard, G. Biotteau, E. Balanzat, and B. Gervais

J. Appl. Phys. 88, 1339 (2000); http://dx.doi.org/10.1063/1.373822 (7 pages) | Cited 3 times

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Natural quartz single crystals (α-SiO2) have been exposed to pulsed heavy ion beams (12C, 19F, 32S) with energies of 1 MeV amu−1 in the electronic slowing down regime. The simultaneous recording of the ion fluence and emitted photons with time-resolved spectroscopy experiments allowed the measurement of the “blue luminescence” time decay at 85 K as a function of the fluence at the various electronic stopping power, Se=(−dE/dx)e, of the ions. For all ions, regardless of fluence, the spectra are similar and have two broad bands centered at 1.60 and 2.75 eV with full widths at half maximum around 0.30 and 0.75 eV, respectively. Single-exponential time decay curves are found regardless of Se increasing from 1.4 keV nm−1 (12 MeV 12C) to 5.2 keV nm−1 (32 MeV 32S) across the amorphous track-formation threshold at 2.5±0.5 keV nm−1. At low damaged fractions (⩽22%), the decay-time constant ranges between 1.0 and 1.6 ms. The luminescence intensities at zero delay time approximately decrease in an exponential fashion versus fluence with a decay cross section increasing by around one order-of-magnitude at the track-formation threshold, as found in the previous experiments with continuous beams. We analyze to which extent the luminescence decay versus fluence could be due to the quenching of the self-trapped exciton (STE) radiative recombinations by interactions with the ion-induced defects. For this, a STE diffusion model is devised where the STEs recombine nonradiatively at the neighboring cylindrical tracks. The model gives luminescence decay curves versus fluence in good agreement with the experimental data by varying the STE diffusion constant and the amorphous track-core radius in a reasonable range of values. © 2000 American Institute of Physics.
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42.70.Ce Glasses, quartz
61.80.Jh Ion radiation effects
78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.47.-p Spectroscopy of solid state dynamics
61.82.Ms Insulators

Uncertainty limits for the macroscopic elastic moduli of random polycrystalline aggregates

Pham Duc Chinh

J. Appl. Phys. 88, 1346 (2000); http://dx.doi.org/10.1063/1.373823 (10 pages) | Cited 17 times

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Practical polycrystalline aggregates are expected to have macroscopic properties that depend upon the properties of constituent crystals and the aggregate geometry. Since that microgeometry is usually random, there will be some uncertainty in the observed macroscopic behavior of the aggregates. The general shape-independent upper and lower estimates for those uncertainty intervals for the elastic moduli of completely random polycrystals are constructed from the minimum energy and complementary energy principles. Applications to aggregates of cubic crystals are presented. © 2000 American Institute of Physics.
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46.25.Cc Theoretical studies

General susceptibility functions for relaxations in disordered systems

R. Bergman

J. Appl. Phys. 88, 1356 (2000); http://dx.doi.org/10.1063/1.373824 (10 pages) | Cited 46 times

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A general equation for the susceptibility of disordered systems is proposed. It is based on the experimental observation of power laws at frequencies far from the peak frequency of the imaginary part of the frequency dependent relaxation function, the susceptibility. The obtained general expression contains the equations of other proposed relaxation functions as special cases and, thus, it might be considered as a generalization of these. From this general equation we derive an equation specially adapted for the α relaxation in glass-forming materials. This equation contains only three fit parameters and it is thus very suitable for fitting real experimental data. It is shown that this equation is a good frequency domain representation of the time domain Kohlrausch–Williams–Watts stretched exponential. From the general equation we also derive a four-parameter “universal” equation that describes most types of responses and even inverted response data, i.e., response peaks more stretched on the low frequency side than on the (as is normal) high frequency side. The physical significance of the different parameters is qualitatively discussed and the proposed functions are shown to satisfactorily describe typical experimental data. © 2000 American Institute of Physics.
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77.22.Gm Dielectric loss and relaxation
78.20.-e Optical properties of bulk materials and thin films

Diffusion of Ge in Si1-xGex/Si single quantum wells in inert and oxidizing ambients

Michelle Griglione, Timothy J. Anderson, Yaser M. Haddara, Mark E. Law, Kevin S. Jones, and Alex van den Bogaard

J. Appl. Phys. 88, 1366 (2000); http://dx.doi.org/10.1063/1.373825 (7 pages) | Cited 16 times

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The interdiffusion of Si/Si0.85Ge0.15/Si single quantum well (SQW) structures subjected to inert- and oxidizing-ambient annealing was investigated as a function of temperature (900–1200 °C) and time. Point defect injection allowed modification of the vacancy and interstitial mediated components of interdiffusion, DV and DI. Diffusion profiles of samples processed in inert and oxidizing ambients were similar, which indicates a vacancy-dominated mechanism. Activation energies of diffusion in inert and oxidizing ambients were found to be 5.8 and 5.0 eV, respectively. A fractional interstitial component fI of ∼0.10 was estimated for the lower temperatures, while a significantly smaller fI of ∼0.02 was estimated for the higher temperatures. Experiments using SQWs with buried boron marker layers showed that dislocations in the Si1-xGex trap point defects and affect interdiffusion behavior. © 2000 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Excimer laser induced diffusion in magnetic semiconductor quantum wells

H. Howari, D. Sands, J. E. Nicholls, J. H. C. Hogg, T. Stirner, and W. E. Hagston

J. Appl. Phys. 88, 1373 (2000); http://dx.doi.org/10.1063/1.373826 (7 pages) | Cited 2 times

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Studies of pulsed laser annealing (PLA) of CdTe/CdMnTe quantum well structures are made in order to examine depth dependent effects in laser irradiated semiconductors. Since diffusion coefficients are strongly dependent on the temperature, depth resolution is achieved because the diffusion of Mn from the barriers into the quantum wells is depth dependent. Multiple quantum well (MQW) structures of CdTe/CdMnTe were annealed with single pulses from an XeCl laser at 308 nm. At a threshold of 90 mJ cm−2 two new emission bands are observed that are attributed to the diffusion of Mn from barrier layers to QWs. The diffusion associated with these bands, measured as the integrated product of the diffusion constant and time, is found to be 300 and 30 Å2. Calculations of the temperature, reached within the surface following PLA, using an analytical solution of the heat diffusion equation coupled with known high temperature diffusion coefficients predict the diffusion to decrease by one order of magnitude within one period at the top of the MQW stack. It is suggested that at the threshold surface melting occurs and that these emission bands arise from the QWs immediately beneath the melt front. The diffusion of Mn ions into the QWs is confirmed by magneto-optical data. A further emission band occurs at this same threshold with a Mn concentration above that of the concentration in the barrier layers of the MQW stack. This emission is attributed tentatively to the segregation of the Mn ion within the molten region following recrystallization. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors

Composition, residual stress, and structural properties of thin tungsten nitride films deposited by reactive magnetron sputtering

Y. G. Shen, Y. W. Mai, D. R. McKenzie, Q. C. Zhang, W. D. McFall, and W. E. McBride

J. Appl. Phys. 88, 1380 (2000); http://dx.doi.org/10.1063/1.373827 (9 pages) | Cited 28 times

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Thin tungsten nitride (WNx) films were produced by reactive dc magnetron sputtering of tungsten in an Ar–N2 gas mixture. The effects of the variation of nitrogen partial pressure on the composition, residual stress, and structural properties of these films as well as the influence of postdeposition annealing have been studied. The films were analyzed in situ by a cantilever beam technique, and ex situ by x-ray photoelectron spectroscopy, electron energy-loss spectroscopy, x-ray diffraction, and transmission electron microscopy (TEM). It was found that at N concentrations below 8 at. %, the films (typical 150 nm in thickness) were essentially bcc α-W. An amorphous phase was observed in the range of about 12–28 at. % N. When N concentrations reached ∼32 at. % or above, a single-phase structure of W2N was formed. Annealing of the as-deposited films resulted in crystallization of the amorphous or an improved crystallinity of the W2N structure, which was related to the N concentration. Stresses of all W and WNx films were compressive. As the N concentration was increased, the stress decreased and reached its lowest value for amorphous samples near 20 at. % N. Past this point, the compression of films rose again. These results can be ascribed to structural changes induced by the pressure-dependent variation in the average energy of particles bombarding the film during deposition. Cross-sectional TEM studies showed that all crystalline WNx films had columnar microstructures. The average column width near stoichiometry of W2N was ∼20±5 nm near the film surface. © 2000 American Institute of Physics.
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68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
61.72.Cc Kinetics of defect formation and annealing
61.66.Bi Elemental solids
61.66.Dk Alloys
61.43.Er Other amorphous solids
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Kz Other electron-impact emission phenomena

A search for strain gradients in gold thin films on substrates using x-ray diffraction

O. S. Leung, A. Munkholm, S. Brennan, and W. D. Nix

J. Appl. Phys. 88, 1389 (2000); http://dx.doi.org/10.1063/1.373828 (8 pages) | Cited 18 times

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The high strengths of gold thin films on silicon substrates have been studied with particular reference to the possible effect of strain gradients. Wafer curvature/thermal cycling measurements have been used to study the strengths of unpassivated, oxide-free gold films ranging in thickness from 0.1 to 2.5 μm. Films thinner than about 1 μm in thickness appear to be weakened by diffusional relaxation effects near the free surface and are not good candidates for the study of strain gradient plasticity. Our search for plastically induced strain gradients was thus limited to thicker films with correspondingly larger grain sizes. Three related x-ray diffraction techniques have been used to investigate the elastic strains in these films. The standard dhkl vs sin2 Ψ technique has been used to find the average strain through the thickness of the films. The results are consistent with wafer curvature measurements. We have also measured a number of dhkl’s as a function of penetration depth to construct depth-dependent dhkl vs sin2 Ψ plots. These data show that the residual elastic strain is essentially independent of depth in the film. Finally, a new technique for sample rotation has been used to measure the dhkl’s for a fixed set of grains in the film as a function of penetration depth. Again, no detectable gradient in strain has been observed. These results show that the high strengths of unpassivated gold films relative to the strength of bulk gold cannot be rationalized on the basis of strain gradients through the film thickness. However, a sharp gradient in strain close to the film substrate interface cannot be ruled out. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity

Formation of Ge nanoislands using a scanning tunneling microscope

Alexander A. Shklyaev, Motoshi Shibata, and Masakazu Ichikawa

J. Appl. Phys. 88, 1397 (2000); http://dx.doi.org/10.1063/1.373829 (4 pages) | Cited 10 times

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Germanium islands were grown on a sample surface by accumulating atoms from the surrounding area through directional surface diffusion initiated by the electric field of a scanning tunneling microscope (STM). The Ge islands grew with a constant rate determined by the tip–sample bias voltage. The parameters of tip–sample interaction were estimated from the kinetic data for island growth by using a scaling relationship among the growth rate, the dipole moment of atoms on surfaces, and the tip–sample bias voltage. The results show that continuous atom transfer with a STM occurs with a rate significantly higher for Ge than for Si. © 2000 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Interface stress in Au/Ni multilayers

K. O. Schweitz, J. Bøttiger, J. Chevallier, R. Feidenhans’l, M. M. Nielsen, and F. B. Rasmussen

J. Appl. Phys. 88, 1401 (2000); http://dx.doi.org/10.1063/1.373830 (6 pages) | Cited 7 times

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The effect of intermixing on the apparent interface stress is studied in 〈111〉-textured dc-magnetron sputtered Au/Ni multilayers by use of two methods commonly used for determining interface stress. The method using profilometry and in-plane x-ray diffraction does not take intermixing into account and yields an apparent interface stress of −8.46±0.99 J m−2. However, observed discrepancies between model calculations and measured high-angle x-ray diffractograms indicate intermixing, and by use of the profilometry and sin2 ψ method the real interface stress value of −2.69±0.43 J m−2 is found. This method also reveals a significant and systematic change of the stress-free lattice parameter of both constituents as a function of modulation period which is shown to account for the difference between the two findings. The method using in-plane diffraction is thus shown to be inapplicable to interface stress determinations in systems exhibiting a modulation period-dependent stress-free lattice parameter. Finally, a deviation of the interface stress in the Au/Ni sample with the smallest modulation period as compared to specimens with larger bilayer lengths is observed to be concurrent with a significant decrease in the interface roughness measured by x-ray reflectivity, which suggests that the deviation is of geometrical origin. © 2000 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.35.Gy Mechanical properties; surface strains

Structural improvement in sublimation epitaxy of 4H–SiC

M. Syväjärvi, R. Yakimova, H. Jacobsson, and E. Janzén

J. Appl. Phys. 88, 1407 (2000); http://dx.doi.org/10.1063/1.373831 (5 pages) | Cited 18 times

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The sublimation epitaxy growth process has been studied. The structural quality of the grown layers improves compared with the substrate mainly due to a diminished domain structure misorientation. Optical microscopy shows that the as-grown surfaces are free of typical defects appearing in silicon carbice (SiC) epitaxy, whereas atomic force microcopy measurements show macrosteps. As a possible technique to produce high-quality 4H–SiC, sublimation epitaxy was performed on substrates containing a layer grown by liquid phase epitaxy which is a growth process for closing micropipes in the initial substrate. In spite of the initial surface roughness of the liquid phase epitaxy layer, the surface morphology of the sublimation grown epilayers remained smooth and the structural quality improvement was maintained. This does not occur if the initial surfaces are too rough. A suggestion for roughness reduction is presented. The growth conditions (growth rate ramp up, growth temperature, temperature gradient, source to substrate distance, and substrate surface orientation) leading to the results are presented. A model for the mechanism for structural improvement is outlined and supporting experimental observations are given. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Growth kinetics of SiO2 on (001) Si catalyzed by Cu3Si at elevated temperatures

H. Y. Huang and L. J. Chen

J. Appl. Phys. 88, 1412 (2000); http://dx.doi.org/10.1063/1.373832 (6 pages) | Cited 1 time

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The oxidation of Si catalyzed by 170-nm-thick Cu3Si at elevated temperatures has been investigated by transmission electron microscopy, glancing angle x-ray diffraction, and Auger electron spectroscopy. For wet oxidation at 140–180 °C, the thickness of the oxide was found to increase parabolically with time with an activation energy of 0.4±0.2 eV. The activation energy is close to that of diffusivity of Cu in Si. At 180–200 °C, the growth rate became slower with increasing temperature. The growth of oxide tended to be discontinuous at the surface as the oxidation temperature was increased to a temperature at or higher than 300 °C. The anomalously fast growth of oxide at low temperatures is attributed to the presence of filamentary structures of Cu clusters in the oxide to expedite the diffusion of the oxidants through oxide. At 200–250 °C, more Cu atoms diffuse to the Cu3Si/Si interface and less Cu atoms stay in the oxide, which slows down the oxide growth. The lack of filamentary structures of Cu as diffusion paths retards the growth of SiO2. At 300 °C or higher temperatures, the lack of filamentary structures of Cu clusters stopped the growth of continuous oxide layer altogether. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
82.20.Hf Product distribution
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.20.Pm Rate constants, reaction cross sections, and activation energies
66.30.Ny Chemical interdiffusion; diffusion barriers

Phase formation and strain relaxation during thermal reaction of Zr and Ti with strained Si1−x−yGexCy epilayers

V. Aubry-Fortuna, G. Tremblay, F. Meyer, Y. Miron, Y. Roichman, M. Eizenberg, F. Fortuna, U. Hörmann, and H. Strunk

J. Appl. Phys. 88, 1418 (2000); http://dx.doi.org/10.1063/1.373833 (6 pages) | Cited 2 times

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Silicides are often used in Si technology for both their ohmic and rectifying properties. In this work, we have compared Zr and Ti germanosilicides as possible metallic contacts on SiGeC alloys in terms of phase formation and stability of the unreacted SiGeC alloy. The germanosilicides are obtained after rapid thermal annealings of Zr or Ti with strained SiGeC layers. The interactions of the metal films with these alloys have been investigated by sheet resistance measurements, x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), and energy dispersive spectroscopy in situ in the TEM. Four crystal x-ray diffraction was performed to measure the residual strain of the unreacted SiGeC epilayer after reaction. The analyses indicate that the final compounds are the C49–Zr(SiGe)2 and C54–Ti(SiGe)2 phases, respectively: In both cases, the compound is formed by monocrystalline grains with various orientations. Nevertheless, neither XRD, nor sheet resistance measurements give any clear information about the C incorporation in the phase, when the reaction occurs with a SiGeC layer. We have observed that the use of Zr completely avoids Ge segregation with an uniform layer formed, while in the case of the reaction with Ti, the grains do not form a continuous layer and Ge-segregation is evidenced: A Ge-rich Si1−z−yGez(Cy) alloy is detected in between the metallic grains. In addition, an early strain relaxation of the unreacted SiGe layer is observed after reaction, and it is much more important after reaction with Ti. During the reaction with nearly compensated SiGeC layers, Zr totally prevents the initial state of strain, while Ti strongly affects the unreacted SiGeC alloy and destroys its initial state. All these results indicate that Zr may be an interesting candidate for realizing germanosilicide contacts on IV–IV alloys, due to its good thermal stability. © 2000 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
73.40.Ns Metal-nonmetal contacts
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
68.35.Dv Composition, segregation; defects and impurities

Photoluminescence and photostimulated luminescence of Tb3+ and Eu3+ in zeolite-Y

Wei Chen, Ramaswami Sammynaiken, and Yining Huang

J. Appl. Phys. 88, 1424 (2000); http://dx.doi.org/10.1063/1.373834 (8 pages) | Cited 39 times

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Tb3+ and Eu3+ were codoped in zeolite-Y. Their photoluminescence and photostimulated luminescence were investigated. Due to the dissipation of excitation energy by OH vibrations, the luminescence from the hydrated zeolite containing Tb3+ and Eu3+ prepared at room temperature is very weak. However, the luminescence is enhanced greatly when the sample was treated at 800 °C. Strong photostimulated luminescence of both Tb3+ and Eu3+ was detected in the sample prepared at 800 °C. The photostimulated luminescence of Tb3+ is due to the recombination of electrons with Tb4+ ions, while the photostimulated luminescence of Eu3+ is caused by energy transfer from Tb3+ to Eu3+. The existence of Tb4+ and Eu2+ ions is due to charge transfer from Eu3+ to Tb3+. The occurrence of photostimulated luminescence and discrete emission lines in blue (434 nm), green (543 nm), and red (611 nm) colors indicate that this material has potential applications in white light-emitting devices and erasable optical storage. © 2000 American Institute of Physics.
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78.55.Hx Other solid inorganic materials

Edge-emission electroluminescence study of as-grown vertical-cavity surface-emitting laser structures

Sandip Ghosh, Stephanie Constant, Thomas J. C. Hosea, and T. E. Sale

J. Appl. Phys. 88, 1432 (2000); http://dx.doi.org/10.1063/1.373835 (7 pages) | Cited 13 times

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We report polarized edge- and front-emission electroluminescence studies on red-emitting vertical-cavity surface-emitting laser (VCSEL) structures. The measurements were performed nondestructively on pieces of as-grown wafers using indium–tin–oxide-coated glass electrodes. The front-emission spectra helped determine the Fabry–Pérot cavity-mode wavelength, while the edge-emission spectra were used to identify the wavelength of ground-state emission from the quantum wells (QWs) in the active region. However, measurements on edge-emitting laser (EEL) structures with a similar QW active region reveal that the peaks of the edge-emission spectra are always slightly redshifted with respect to front emission. We show that this arises due to reabsorption effects and then appropriately correct for it in the VCSELs by studying such shifts in the equivalent EELs. Thereafter, by comparing the experimental results with theoretical calculations and simulations, we estimate the composition, strain, and material quality of the QWs in the VCSEL active regions. Finally, we comment on the usefulness of comparing the two orthogonally polarized edge-emission spectra. © 2000 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.60.Fi Electroluminescence

Photoluminescence and Raman scattering of silicon nanocrystals prepared by silicon ion implantion into SiO2 films

G. H. Li, K. Ding, Y. Chen, H. X. Han, and Z. P. Wang

J. Appl. Phys. 88, 1439 (2000); http://dx.doi.org/10.1063/1.373836 (4 pages) | Cited 22 times

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Photoluminescence (PL) and Raman spectra of silicon nanocrystals prepared by Si ion implantion into SiO2 layers on Si substrate have been measured at room temperature. Their dependence on annealing temperature was investigated in detail. The PL peaks observed in the as-implanted sample originate from the defects in SiO2 layers caused by ion implantation. They actually disappear after thermal annealing at 800 °C. The PL peak from silicon nanocrystals was observed when thermal annealing temperatures are higher than 900 °C. The PL peak is redshifted to 1.7 eV and the intensity reaches maximum at the thermal annealing temperature of 1100 °C. The characterized Raman scattering peak of silicon nanocrystals was observed by using a right angle scattering configuration. The Raman signal related to the silicon nanocrystals appears only in the samples annealed at temperature above 900 °C. It further proves the formation of silicon nanocrystals in these samples. © 2000 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
61.72.up Other materials
61.80.Jh Ion radiation effects
61.82.Ms Insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Photoluminescence of erbium-doped silicon: Excitation power and temperature dependence

D. T. X. Thao, C. A. J. Ammerlaan, and T. Gregorkiewicz

J. Appl. Phys. 88, 1443 (2000); http://dx.doi.org/10.1063/1.373837 (13 pages) | Cited 14 times

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Photoluminescence measurements have been made on float-zone and Czochralski-grown silicon samples which were doped with erbium by ion implantation. The characteristic luminescence spectra in the wavelength range between 1.5 and 1.6 μm were observed. Differences in the multiple line structure of the spectra indicated that the active luminescent centers have different symmetries and atomic structure. The dependence of the photoluminescence intensity on the laser excitation power and on the temperature was measured. Results are discussed on the basis of a physical model which includes the formation of free excitons, the binding of excitons to erbium ions, the excitation of 4f inner-shell electrons of the erbium ions, and their subsequent decay by light emission. To obtain a quantitative agreement between model analysis and experimental data the consideration of Auger processes by which erbium-bound excitons and erbium ions in excited state can decay by dissipating energy to conduction band electrons appears to be required. From the temperature dependence two activation energies are derived which are associated with the exciton binding energies and with an energy transfer process from excited erbium ions back to erbium-bound excitons, respectively. A good quantitative agreement can be obtained for suitable values of the model parameters. The luminescent properties of the samples of the different types of crystalline silicon are remarkably similar. © 2000 American Institute of Physics.
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78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
71.35.-y Excitons and related phenomena

Optical properties of fluorinated diamond-like carbon films produced by pulsed glow discharge plasma immersion ion processing

M. Hakovirta, X. M. He, and M. Nastasi

J. Appl. Phys. 88, 1456 (2000); http://dx.doi.org/10.1063/1.373838 (4 pages) | Cited 16 times

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Pulsed glow discharge plasma from a 1 Pa gas mixture of acetylene (C2H2) and hexafluoroethane (C2F6) was used to produce fluorinated diamond-like carbon (F-DLC) films on glass and polymethyl-methacrylate (PMMA) substrate. The composition of the F-DLC coatings was measured by using Rutherford backscattering spectroscopy and elastic recoil detection analysis techniques. The transmittance, absorption coefficient, and optical band gap of 100 nm thick F-DLC coatings was measured by using an ultraviolet/visible spectrometer. The friction and wear properties were measured with a conventional pin-on-disk device. In addition, contact angle measurements were taken in order to determine the nonwetting properties of the coatings. The results showed an increase in nonwetting properties, transmittance, and optical band gap with increasing fluorine content in the coatings. The increased fluorine contents suppressed the incorporation of hydrogen and increased the optical band gap energy, which is quite different from the general DLC films whose optical properties are highly improved with increasing amount of hydrogen incorporated in the films. Furthermore, the F-DLC coatings on PMMA and glass substrates proved to have low friction and wear and similar nonwetting properties such as Teflon®.
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78.66.Li Other semiconductors
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
68.60.Dv Thermal stability; thermal effects

Strain variation with sample thickness in GaN grown by hydride vapor phase epitaxy

D. C. Reynolds, D. C. Look, B. Jogai, J. E. Hoelscher, R. E. Sherriff, and R. J. Molnar

J. Appl. Phys. 88, 1460 (2000); http://dx.doi.org/10.1063/1.373839 (4 pages) | Cited 20 times

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High quality GaN crystals can be grown on sapphire by hydride vapor phase epitaxy. The thermal expansion mismatch between sapphire and GaN produces strain in the GaN crystal as it is cooled from the growth temperature to room temperature. The strain is evidenced by shifts in the photoluminescence and reflectance line positions. By analyzing the surface strain as the crystal thickness is increased, the thickness required to obtain zero surface strain can be estimated. This structure might provide a lattice matched and thermally matched substrate for further epitaxial growth of GaN. © 2000 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.60.Dv Thermal stability; thermal effects
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
65.40.De Thermal expansion; thermomechanical effects
78.20.-e Optical properties of bulk materials and thin films
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