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26 Feb 2001

Volume 78, Issue 9, pp. 1171-1311

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Critical cooling rate and thermal stability of Zr–Ti–Cu–Ni–Be alloys

Theodore A. Waniuk, Jan Schroers, and William L. Johnson

Appl. Phys. Lett. 78, 1213 (2001); http://dx.doi.org/10.1063/1.1350624 (3 pages) | Cited 68 times

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The critical cooling rate as well as the thermal stability are measured for a series of alloys in the Zr–Ti–Cu–Ni–Be system. Upon cooling from the molten state with different rates, alloys with compositions ranging along a tie line from (Zr70Ti30)55(Ni39Cu61)25Be20 to (Zr85Ti15)55(Ni57Cu43)22.5Be27.5 show a continuous increase in the critical cooling rate to suppress crystallization. In contrast, thermal analysis of the same alloys shows that the undercooled liquid region, the temperature difference between the glass transition temperature and the crystallization temperature, is largest for some compositions midway between the two endpoints, revealing that glass forming ability does not correlate with thermal stability. The relationship between the composition-dependent glass forming ability and thermal stability is discussed with reference to a chemical decomposition process. © 2001 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.43.Fs Glasses

Electronic and chemical passivation of hexagonal 6H–SiC surfaces by hydrogen termination

N. Sieber, B. F. Mantel, Th. Seyller, J. Ristein, L. Ley, T. Heller, D. R. Batchelor, and D. Schmeißer

Appl. Phys. Lett. 78, 1216 (2001); http://dx.doi.org/10.1063/1.1351845 (3 pages) | Cited 32 times

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Hydrogenation of 6H–SiC (0001) and (000math) is achieved by high-temperature hydrogen treatment. Both surfaces show a low-energy electron diffraction pattern representative of unreconstructed surfaces of extremely high crystallographic order. On SiC(0001), hydrogenation is confirmed by the observation of sharp Si–H stretching modes. The absence of surface band bending for n- and p-type samples is indicative of electronically passivated surfaces with densities of charged surface states in the gap of below 7×1010 cm−2 for p-type and 1.7×1012 cm−2 for n- type samples, respectively. Even after two days in air, the surfaces show no sign of surface oxide in x-ray photoelectron spectroscopy. © 2001 American Institute of Physics.
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81.65.Rv Passivation
81.05.Hd Other semiconductors
68.35.Dv Composition, segregation; defects and impurities
73.20.At Surface states, band structure, electron density of states

Effective compliant substrate for low-dislocation relaxed SiGe growth

Y. H. Luo, J. L. Liu, G. Jin, J. Wan, K. L. Wang, C. D. Moore, M. S. Goorsky, C. Chih, and K. N. Tu

Appl. Phys. Lett. 78, 1219 (2001); http://dx.doi.org/10.1063/1.1351520 (3 pages) | Cited 20 times

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An effective compliant substrate was fabricated for the growth of high-quality relaxed SiGe templates, by synthesizing a 20% B2O3 concentration borosilicate glass (BSG) in the silicon on insulator wafers. Substrates with 5%, 10%, and 20% B2O3 were used for 150 nm Si0.75Ge0.25 epitaxy. Double-axis x-ray diffraction measurements determined the relaxation and composition of the Si1−xGex layers. Cross-sectional transmission electron microscopy was used to observe the lattice of the SiGe epilayer and the Si substrate, dislocation density, and distribution. Raman spectroscopy was combined with step etch to study the samples. The strain sharing effect of the 20% BSG substrate was demonstrated. Thus, we concluded that this compliant substrate is a highly promising candidate for the growth of low-dislocation relaxed SiGe layers. © 2001 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.05.Hd Other semiconductors
78.66.Li Other semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.Nq Composition and phase identification

Spatial variation of luminescence in thick GaN films

F. Bertram, S. Srinivasan, F. A. Ponce, T. Riemann, J. Christen, and R. J. Molnar

Appl. Phys. Lett. 78, 1222 (2001); http://dx.doi.org/10.1063/1.1350594 (3 pages) | Cited 9 times

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The spatial variation of the optical properties of hydride vapor-phase epitaxial GaN layers of various thickness has been studied using scanning cathodoluminescence microscopy. A strong improvement of these properties with film thickness is observed in plan view. Cross-sectional studies show a strong redshift of the luminescence in the vicinity of the substrate within a typical thickness of about 2 μm, reflecting a high local impurity content. Above this initial growth region, a strong blueshift is observed up to the energy of fully relaxed high-purity GaN, indicating vertical strain relaxation as well as depletion of residual donors. This is accompanied by a sharp increase in the lateral spectral homogeneity, indicative of a significant improvement in crystalline quality. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties

Effect of hydrogen on the photoluminescence of Si nanocrystals embedded in a SiO2 matrix

S. Cheylan and R. G. Elliman

Appl. Phys. Lett. 78, 1225 (2001); http://dx.doi.org/10.1063/1.1338492 (3 pages) | Cited 33 times

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Hydrogen passivation of Si nanocrystals is shown to result in a redshift of photoluminescence (PL) emission spectra, as well as the more commonly observed intensity increase. The shift is reversible, with spectra returning to their unpassivated values as hydrogen is removed from the samples by annealing. The magnitude of the redshift also depends on the implant fluence employed for nanocrystal synthesis, increasing with increasing fluence or particle size. These data are shown to be consistent with a model in which larger crystallites are assumed to contain a greater number of nonradiative defects, i.e., the number of nonradiative defects is assumed to scale with the surface area or volume of a nanocrystal. Hydrogen passivation then results in a disproportionate increase in emission from larger crystallites, giving rise to an apparent redshift in the composite PL emission spectrum. © 2001 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.82.Rx Nanocrystalline materials
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors

Self-assembled metallic dots and antidots: Epitaxial Co on Ru(0001)

Chengtao Yu, Dongqi Li, J. Pearson, and S. D. Bader

Appl. Phys. Lett. 78, 1228 (2001); http://dx.doi.org/10.1063/1.1351522 (3 pages) | Cited 19 times

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We have grown ∼ 1–420 nm thick epitaxial Co wedges on Ru(0001) with molecular-beam epitaxy at 350 °C and characterized them with atomic force microscopy. A metal-on-metal growth mode was observed where three-dimensional islands (dots) or a flat film network with holes (antidots) in truncated pyramidal shapes exist below or above ∼ 20 nm, respectively. The top of the islands and the rim of the holes are flat with a roughness of ∼0.3 nm, and the lateral sizes of these dots/antidots, ∼ 102 nm, tend to be uniform. We suggest that this self-assembled growth be mainly driven by strain. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Ab initio study of substitutional nitrogen in GaAs

W. Orellana and A. C. Ferraz

Appl. Phys. Lett. 78, 1231 (2001); http://dx.doi.org/10.1063/1.1351524 (3 pages) | Cited 11 times

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We investigate the atomic geometry, formation energies, and electronic structure of nitrogen occupying both arsenic and gallium sites in GaAs (NAs and NGa) using first-principles total-energy calculations. We find that both neutral defects induce impurity-like empty levels in the band gap acting as acceptors. While NAs shows a s-like a1 level in the middle of the band gap, NGa shows a p-like t2 level close to the bottom of the conduction band. The gap level of NAs gives theoretical support for the experimentally observed band-edge redshift on the GaAsN alloy for a N concentration ∼3%. Strong inward relaxations preserving the Td symmetry characterize the NAs equilibrium geometry in all the charge states investigated. In contrast, NGa exhibits a structural metastability in neutral charge state and Jahn–Teller off-center distortions in negative charge states forming a negative-U center. Formation energies of competing NAs and NGa defects are also discussed. © 2001 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Evidence for negatively charged vacancy defects in 6H-SiC after low-energy proton implantation

D. T. Britton, M.-F. Barthe, C. Corbel, A. Hempel, L. Henry, P. Desgardin, W. Bauer-Kugelmann, G. Kögel, P. Sperr, and W. Triftshäuser

Appl. Phys. Lett. 78, 1234 (2001); http://dx.doi.org/10.1063/1.1350961 (3 pages) | Cited 19 times

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We have used pulsed-slow-positron-beam-based positron lifetime spectroscopy to investigate the nature of acceptors and charge states of vacancy-type defects in low-energy proton-implanted 6H-SiC(H). We can infer from the temperature dependence of the lifetime spectra that neutral and negatively charged vacancy clusters exist in the track region. Depending on annealing, they give rise to positron lifetimes of 257±2, 281±4, and 345±2 ps, respectively. The 281 ps cluster likely has an ionization level near the middle of the band gap. By comparison with theory, the 257 and 280 ps are identified as (VC–VSi)2 and (VC–VSi)3 clusters, respectively. In addition, other acceptors of ionic type act as strong trapping centers at low temperature (T<150 K). Neutral monovacancy-like complexes are also detected with a lifetime of 160±2 after 900 °C annealing. © 2001 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters
78.70.Bj Positron annihilation
61.72.up Other materials
61.72.Cc Kinetics of defect formation and annealing
71.55.Ht Other nonmetals

Band gap engineering based on MgxZn1−xO and CdyZn1−yO ternary alloy films

T. Makino, Y. Segawa, M. Kawasaki, A. Ohtomo, R. Shiroki, K. Tamura, T. Yasuda, and H. Koinuma

Appl. Phys. Lett. 78, 1237 (2001); http://dx.doi.org/10.1063/1.1350632 (3 pages) | Cited 229 times

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We describe the structural and optical properties of II–VI oxide alloys, MgxZn1−xO and CdyZn1−yO, grown by pulsed-laser deposition. Single-phase alloyed films of (Mg,Zn)O and (Cd,Zn)O with c-axis orientations were epitaxially grown on sapphire (0001) substrates. The maximum magnesium and cadmium concentrations (x=0.33 and y=0.07, respectively) were significantly larger than the thermodynamic solubility limits. The band gap energies systematically changed from 3.0 (y = 0.07) to 4.0 eV (x = 0.33) at room temperature. The photoluminescence peak energy deduced at 4.2 K could be tuned from 3.19 to 3.87 eV by using Cd0.07Zn0.93O and Mg0.33Zn0.67O at both ends, respectively. The lattice constants of the a axis were monotonically increasing functions of the concentrations of both alloys. The exciton–phonon coupling strength was determined in Cd0.01Zn0.99O grown on a lattice-matched ScAlMgO4 substrate. © 2001 American Institute of Physics.
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78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
63.20.kk Phonon interactions with other quasiparticles

Influence of intraband transitions on the electron thermoreflectance response of metals

Andrew N. Smith and Pamela M. Norris

Appl. Phys. Lett. 78, 1240 (2001); http://dx.doi.org/10.1063/1.1351523 (3 pages) | Cited 26 times

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Ultrashort pulsed lasers have repeatedly been demonstrated as effective tools for the observation of transport properties on atomistic time and length scales. Transient thermoreflectance scans of a Au thin film taken using a 200 fs pulsed laser are compared to the parabolic two step model using both the assumption of a linear relationship between reflectance and temperature and using an intraband reflectance model. In this study, the incident photon energy was less than the interband transition energy, therefore the thermoreflectance response is primarily due to intraband transitions. The intraband transitions are influenced by the electron and lattice temperatures through the electron collisional frequency. © 2001 American Institute of Physics.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.66.Bz Metals and metallic alloys
78.47.-p Spectroscopy of solid state dynamics
63.20.K- Phonon interactions

Uniform deposition of ultrathin polymer films on the surfaces of Al2O3 nanoparticles by a plasma treatment

Donglu Shi, S. X. Wang, Wim J. van Ooij, L. M. Wang, Jiangang Zhao, and Zhou Yu

Appl. Phys. Lett. 78, 1243 (2001); http://dx.doi.org/10.1063/1.1352700 (3 pages) | Cited 44 times

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Surface modification of nanoparticles will present great challenges due to their extremely small dimensions, high surface areas, and high surface energies. In this research, we demonstrate the uniform deposition of ultrathin polymer films of 2 nm on the surfaces of alumina nanoparticles. The deposited film can also be tailored to multilayers. Time-of-flight secondary ion mass spectroscopy was used to confirm the pyrrole thin film on the nanoparticle surfaces. Using such a nanocoating, it is possible to alter the intrinsic properties of materials that cannot be achieved by conventional methods and materials. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
61.41.+e Polymers, elastomers, and plastics
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.65.-b Surface treatments
52.77.-j Plasma applications
82.35.-x Polymers: properties; reactions; polymerization
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Emission properties of an amorphous AlN:Cr3+ thin-film phosphor

M. L. Caldwell, A. L. Martin, V. I. Dimitrova, P. G. Van Patten, M. E. Kordesch, and H. H. Richardson

Appl. Phys. Lett. 78, 1246 (2001); http://dx.doi.org/10.1063/1.1351531 (3 pages) | Cited 22 times

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Chromium-doped aluminum nitride (AlN:Cr) films were grown on p-doped silicon (111) by rf magnetron sputtering in a nitrogen atmosphere at a pressure of 10−4 Torr. Film thickness was typically 200 nm. After growth, the films were “activated” at ∼1300 K for 30 min in a nitrogen atmosphere. Films activated in this manner exhibit intense cathodoluminescence and photoluminescence emission. Spectral evidence demonstrates conclusively that the luminescent centers are Cr3+ ions. © 2001 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors
81.15.Cd Deposition by sputtering
81.05.Gc Amorphous semiconductors

1.6 μm emission from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses

Yong Gyu Choi, Kyong Hon Kim, Bong Je Park, and Jong Heo

Appl. Phys. Lett. 78, 1249 (2001); http://dx.doi.org/10.1063/1.1350958 (3 pages) | Cited 35 times

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1.6 μm emission originated from Pr3+: (3F3,3F4)→3H4 transition in Pr3+- and Pr3+/Er3+-doped selenide glasses were investigated under an optical pump of a conventional 1480 nm laser diode. The measured peak wavelength and full width at half maximum of the fluorescent emission were ∼ 1650 and >100 nm, respectively. A moderate lifetime of the thermally coupled upper manifolds ( ∼ 212±5 μs) together with a high stimulated emission cross section of ∼ (3±1)×10−20 cm2 promises to be useful for 1.6 μm band fiber-optic amplifier that can be pumped with an existing high-power laser diode. Codoping of Er3+ significantly enhanced the emission intensity by way of a nonradiative Er3+: 4I13/2→Pr3+: (3F3,3F4) energy transfer. © 2001 American Institute of Physics.
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78.45.+h Stimulated emission
78.55.Hx Other solid inorganic materials
42.55.Wd Fiber lasers

High internal electric field in a graded-width InGaN/GaN quantum well: Accurate determination by time-resolved photoluminescence spectroscopy

P. Lefebvre, A. Morel, M. Gallart, T. Taliercio, J. Allègre, B. Gil, H. Mathieu, B. Damilano, N. Grandjean, and J. Massies

Appl. Phys. Lett. 78, 1252 (2001); http://dx.doi.org/10.1063/1.1351517 (3 pages) | Cited 94 times

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Time-resolved photoluminescence (PL), at T = 8 K, is used to study a graded-width InGaN/GaN quantum well. Across the sample, the well width continuously varies from ∼5.5 to 2.0 nm corresponding to PL peak energies varying between 2.0 and 2.9 eV and to PL decay rates covering four orders of magnitude. The plot of decay times versus PL energies is very well fitted by a calculation of the electron–hole recombination probability versus well width. The only fitting parameter is the electric field in the well, which we find equal to 2.45±0.25 MV/cm, in excellent agreement with experimental Stokes shifts for this type of samples. © 2001 American Institute of Physics.
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78.67.De Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Cr III-V semiconductors
73.63.Hs Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Origin of the domain contrast on a Si(001)-2×1 surface imaged by secondary electrons

Heiji Watanabe, Masakazu Ichikawa, and Takaaki Kawamura

Appl. Phys. Lett. 78, 1255 (2001); http://dx.doi.org/10.1063/1.1352050 (3 pages) | Cited 3 times

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Secondary electron (SE) imaging of alternating domains on Si(001)-2×1 surfaces was studied. We experimentally investigated the relationship between the domain contrast and the incident electron-beam angles, and found that the domain contrast between alternating 2×1 terraces is reversed by changing the incident-beam-angle conditions. And we theoretically show that the intensity of electron waves near the surface changes drastically and reverses according to the incident beam conditions. Both these experimental and theoretical results indicate that the domain contrast in SE images does not originate from anisotropic SE emission from the reconstructed surface but from the difference between the SE excitation on the 2×1 terrace and that on the 1×2 terrace. © 2001 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
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