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25 Nov 2002

Volume 81, Issue 22, pp. 4103-4293

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Polarization effects in photoluminescence of C- and M-plane GaN/AlGaN multiple quantum wells

E. Kuokstis, C. Q. Chen, M. E. Gaevski, W. H. Sun, J. W. Yang, G. Simin, M. Asif Khan, H. P. Maruska, D. W. Hill, M. C. Chou, J. J. Gallagher, and B. Chai

Appl. Phys. Lett. 81, 4130 (2002); http://dx.doi.org/10.1063/1.1524298 (3 pages) | Cited 46 times

Online Publication Date: 19 November 2002

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Polarization effects have been studied in GaN/AlGaN multiple quantum wells (MQWs) with different c-axis orientation by means of excitation-dependent photoluminescence (PL) analysis. Quantum structures were grown on [0001]-oriented sapphire substrates (C plane) and single-crystalline [1math00]-oriented freestanding GaN (M plane) using the metalorganic chemical vapor deposition technique. Strong PL spectrum line blueshifts (up to 140 meV) which are correlated with the excitation intensity have been obtained for C-plane MQWs, whereas no shift has been observed for M-plane MQWs. Theoretical calculations and comparison with the PL data confirm that the built-in electric field for C-plane structures is much stronger than the field present for M-plane MQWs. In the former case, the excitation-induced blueshift of the PL line is due to the screening of the built-in electric field by photoinjected carriers, which is consistent with the field strength of 1.23 MV/cm in the absence of excitation. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Melting and expansion behavior of indium in carbon nanotubes

Yihua Gao, Yoshio Bando, and Dmitri Golberg

Appl. Phys. Lett. 81, 4133 (2002); http://dx.doi.org/10.1063/1.1524293 (3 pages) | Cited 16 times

Online Publication Date: 19 November 2002

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Indium-filled carbon nanotubes were synthesized via a simple chemical vapor deposition. The carbon nanotubes had diameters of 100–200 nm and length of ∼10 μm. The melting and expansion behavior of the indium in carbon nanotubes were investigated in an analytical transmission electron microscope. It was found that the melting and expansion behavior of indium were different from that in a macroscopic state. The melting behavior was explained using a particular equation developed for a nanoscale indium column. The analysis of the expansion behavior allows us to clarify the problems of indium filling usage in carbon nanotube-based nanothermometer. © 2002 American Institute of Physics.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.-w Structure of nanoscale materials
64.70.Nd Structural transitions in nanoscale materials
62.25.-g Mechanical properties of nanoscale systems
81.07.De Nanotubes
64.70.D- Solid-liquid transitions
65.20.-w Thermal properties of liquids
65.40.De Thermal expansion; thermomechanical effects
07.20.Dt Thermometers
68.37.Lp Transmission electron microscopy (TEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.03.Cd Surface tension and related phenomena

Formation of face-centered-cubic zirconium by mechanical attrition

I. Manna, P. P. Chattopadhyay, F. Banhart, and H.-J. Fecht

Appl. Phys. Lett. 81, 4136 (2002); http://dx.doi.org/10.1063/1.1519942 (3 pages) | Cited 20 times

Online Publication Date: 19 November 2002

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This study reports a hcp→fcc polymorphic transformation in elemental zirconium induced by mechanical attrition in a planetary ball mill. The transformation is monitored and verified by x-ray and electron diffraction and high-resolution transmission electron microscopy. Grain size decreases and lattice parameter increases with continued milling. The phase change is gradual and is accompanied by about 9% increase in volume per atom. It is suggested that structural instability due to plastic strain, increasing lattice expansion, and negative (from core to boundary) hydrostatic pressure is responsible for this hcp→fcc polymorphic transformation in zirconium. © 2002 American Institute of Physics.
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61.50.Ks Crystallographic aspects of phase transformations; pressure effects
64.70.K- Solid-solid transitions
81.20.Wk Machining, milling
81.05.Bx Metals, semimetals, and alloys
61.66.Bi Elemental solids
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder

Thermal stress hardening of a-Si3N4/nc-TiN nanostructured multilayers

Junhua Xu, Lihua Yu, Yasushi Azuma, Toshiyuki Fujimoto, Hiroyuki Umehara, and Isao Kojima

Appl. Phys. Lett. 81, 4139 (2002); http://dx.doi.org/10.1063/1.1525852 (3 pages) | Cited 15 times

Online Publication Date: 19 November 2002

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Amorphous/nanopolycrystalline Si3N4/TiN nanostructured multilayer films have been fabricated by radio-frequency reactive magnetron sputtering. The effects of deposition temperature, modulation period, and the layer thickness ratio on the hardness have been studied, in order to elucidate the hardening mechanisms in these multilayers. The hardness of the Si3N4/TiN multilayers is affected not only by the modulation periods, but also by the layer thickness ratio and deposition temperature. The hardness value is about 40% higher than the value calculated from the rule of mixtures at a deposition temperature of 500 °C and a modulation ratio (lSi3N4/lTiN) of 3/1. Based on the experimental results, it is suggested that the alternating stress field caused by thermal mismatch between Si3N4 and TiN is one of the main reasons for the superhardness effect in Si3N4/TiN nanostructured multilayers. © 2002 American Institute of Physics.
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68.65.Ac Multilayers
68.35.Gy Mechanical properties; surface strains
62.25.-g Mechanical properties of nanoscale systems
61.43.Er Other amorphous solids
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.15.Cd Deposition by sputtering
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
81.07.Bc Nanocrystalline materials

Growth of GaN films on porous SiC substrate by molecular-beam epitaxy

F. Yun, M. A. Reshchikov, L. He, H. Morkoç, C. K. Inoki, and T. S. Kuan

Appl. Phys. Lett. 81, 4142 (2002); http://dx.doi.org/10.1063/1.1524304 (3 pages) | Cited 11 times

Online Publication Date: 19 November 2002

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Porous SiC (PSiC) substrates were used for the growth of GaN by reactive molecular-beam epitaxy with ammonia as the nitrogen source. Improved quality of GaN films has been demonstrated for growth on PSiC substrates, as compared to that on standard 6H–SiC substrates. Cross-sectional transmission electron microscopy and electron diffraction showed a reduction in dislocation density and a higher degree of lattice and thermal relaxation in the GaN films grown on porous substrates. The submicron GaN films exhibit a rocking curve linewidth of 3.3 arcmin for (0002) diffraction and 13.7 arcmin for (10math2) diffraction. Low-temperature photoluminescence showed an excitonic transition with a full width at half maximum of 9.5 meV at 15 K, as well as high quantum efficiency, on the GaN layer grown on PSiC when the thin skin layer on porous SiC was removed before growth. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Ultraviolet light emission from self-organized p–n domains in cubic boron nitride bulk single crystals grown under high pressure

T. Taniguchi, K. Watanabe, S. Koizumi, I. Sakaguchi, T. Sekiguchi, and S. Yamaoka

Appl. Phys. Lett. 81, 4145 (2002); http://dx.doi.org/10.1063/1.1524295 (3 pages) | Cited 16 times

Online Publication Date: 19 November 2002

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Ultraviolet light emission at a wavelength of 250 nm was observed from Be-doped single crystals of cubic boron nitride (cBN) grown at high pressure and high temperatures. We found that dopants of Be were localized in the grown crystals when a small amount of Be was added to the crystals. The crystals had boundaries of blue-colored Be-rich regions and amber-colored ones. These colored regions were divided by the boundaries of growth sectors. When a direct current was induced across the boundaries, UV light emission was clearly observed. The crystals may include self-organized p–n regions along the growth sectors. Although some crystalline imperfections still prevent the crystals from exhibiting properties of materials that can emit UV light with a wide band gap (6.3 eV), it is noticeable that bulk single crystals have been synthesized that contain self-organized p–n boundaries and show UV light emission. © 2002 American Institute of Physics.
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78.60.Fi Electroluminescence
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
62.50.-p High-pressure effects in solids and liquids
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Photopyroelectric structural and thermal characterization of first-order phase transition in liquid crystals

F. Mercuri, R. Pizzoferrato, U. Zammit, and M. Marinelli

Appl. Phys. Lett. 81, 4148 (2002); http://dx.doi.org/10.1063/1.1524290 (3 pages) | Cited 9 times

Online Publication Date: 19 November 2002

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A photopyroelectric setup, which allows the study of the thermal behavior and the structural evolution of 8CB liquid crystal at the first-order nematic–isotropic phase transition, is presented. It is shown that the kinetics of the transition in liquid-crystal films are not the same on heating and cooling, and a quantitative determination of the width of the two-phase coexistence region is reported. A correlation between the photopyroelectric signal and the liquid-crystal morphology in the coexistence region has been found. © 2002 American Institute of Physics.
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64.70.M- Transitions in liquid crystals
77.70.+a Pyroelectric and electrocaloric effects
72.40.+w Photoconduction and photovoltaic effects

Enhanced thermal stability of strong gratings written in H-loaded tin-phosphosilicate optical fibers

Gilberto Brambilla

Appl. Phys. Lett. 81, 4151 (2002); http://dx.doi.org/10.1063/1.1525850 (3 pages) | Cited 3 times

Online Publication Date: 19 November 2002

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Enhanced photosensitivity has been observed in hydrogen-loaded tin-phosphosilicate fibers by using a 248 nm excimer laser. Isothermal measurements up to 860 K demonstrated significant advantages over fiber gratings written in conventional H-loaded fibers. © 2002 American Institute of Physics.
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42.79.Dj Gratings
42.81.Wg Other fiber-optical devices
42.40.Eq Holographic optical elements; holographic gratings

Blue cathodoluminescence from Ba2B5O9Cl:Eu phosphor thin films on glass substrates

Jianhua Hao and Michael Cocivera

Appl. Phys. Lett. 81, 4154 (2002); http://dx.doi.org/10.1063/1.1525879 (3 pages) | Cited 25 times

Online Publication Date: 19 November 2002

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Spray pyrolysis was used to deposit thin films of Ba2B5O9Cl:Eu from aqueous solutions containing Eu3+. Blue cathodoluminescence due to the abnormal reduction of Eu3+→Eu2+ in as-grown thin films was observed at the growth temperatures from 140 °C to 500 °C. Significant line narrowing was found as the growth temperature increased. Using either conventional or rapid thermal annealing of thin films in air enhanced the transition of the emission spectrum from several peaks to a sharp single peak. Our results also provide the possibility of tuning the blue emission at temperatures suitable for the use of glass substrates in flat panel applications. © 2002 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Nk Insulators
81.15.Rs Spray coating techniques
81.40.Tv Optical and dielectric properties related to treatment conditions
68.55.A- Nucleation and growth
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Cy Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
61.82.Ms Insulators

Thermal stability of polycrystalline silicon/metal oxide interfaces

A. Callegari, E. Gousev, T. Zabel, D. Lacey, M. Gribelyuk, and P. Jamison

Appl. Phys. Lett. 81, 4157 (2002); http://dx.doi.org/10.1063/1.1526150 (2 pages) | Cited 2 times

Online Publication Date: 19 November 2002

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The thermal stability of polycrystalline silicon (poly-Si)/ZrO2 interface was significantly enhanced when the poly-Si was plasma deposited using silane heavily diluted in He. With regard to this process, transmission electron microscopy shows a sharp poly-Si/ZrO2 interface that is stable at 1000 °C. When the poly-Si was deposited by chemical vapor deposition using undiluted silane gas, transmission electron microscopy shows strong reactions at the poly-Si/ZrO2 interface when annealed at 1000 °C. The increased stability can be attributed to He dilution, which may prevent hydrogen from reducing the metal oxide. Another explanation may be directly related to He-excited plasma, which is known to produce denser and more stable films. © 2002 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
68.35.Ct Interface structure and roughness
68.37.Lp Transmission electron microscopy (TEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

High-temperature centrifugation: a tool for finding eutectic compositions in multicomponent alloys

Jörg F. Löffler, Sven Bossuyt, Atakan Peker, and William L. Johnson

Appl. Phys. Lett. 81, 4159 (2002); http://dx.doi.org/10.1063/1.1522820 (3 pages) | Cited 8 times

Online Publication Date: 19 November 2002

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A metallic melt of composition Al52.6Cu13.4Ge28Si6 was processed for 2 h in a centrifuge at a temperature of 530 °C and inertial acceleration of 60 000 g (g = gravitational acceleration), and then slowly cooled to room temperature during continuous centrifugation. Primary phases forming in the melt during cooling were sequentially separated from the remaining liquid, changing the composition of the liquid, until it solidified in a ternary eutectic microstructure of composition Al64Cu3Ge33. Presenting scanning electron microscope images, we demonstrate that this method of high-temperature centrifugation is a efficient tool to isolate and identify multiphase eutectic compositions and the sequence of crystallization in multicomponent alloys. The latter is particularly useful for the discovery of new bulk metallic glasses. © 2002 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
64.75.-g Phase equilibria
64.70.D- Solid-liquid transitions
81.05.Kf Glasses (including metallic glasses)

Study of the relaxation process during InGaAs/GaAs (001) growth from in situ real-time stress measurements

M. U. González, Y. González, and L. González

Appl. Phys. Lett. 81, 4162 (2002); http://dx.doi.org/10.1063/1.1524303 (3 pages) | Cited 8 times

Online Publication Date: 19 November 2002

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Strain evolution during In0.2Ga0.8As/GaAs (001) growth by molecular beam epitaxy has been monitored in real time. We have detected that three main relaxation stages, related to different mechanisms, take place during growth, and we have obtained the thickness range where those mechanisms are active. The in situ measured relaxation behavior in the plastic stages has been described by means of a simple equilibrium model that takes into account dislocations generation and interaction between them. The excellent agreement between the experimental data and the model allows us to determine the value of the formation energy per unit length of a misfit dislocation and the extent of the interaction between dislocations in this material system. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors

Patterning organic light-emitting diodes by cathode transfer

Jungsoo Rhee and Hong H. Lee

Appl. Phys. Lett. 81, 4165 (2002); http://dx.doi.org/10.1063/1.1525878 (3 pages) | Cited 22 times

Online Publication Date: 19 November 2002

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A technique is presented for patterning the metal cathode of organic light-emitting diodes that allows for cathode engineering. The technique involves transferring pretreated and prepatterned metal on a substrate onto the surface of organic layers of the device by pressing, utilizing a difference in the adhesion strength of the metal between the substrate and the underlying organic layer. This cathode transfer technique is applied to fabricating a 20×10 passive matrix display with a pixel size of 250 μm by 250 μm. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems

Electromigration-induced plastic deformation in passivated metal lines

B. C. Valek, J. C. Bravman, N. Tamura, A. A. MacDowell, R. S. Celestre, H. A. Padmore, R. Spolenak, W. L. Brown, B. W. Batterman, and J. R. Patel

Appl. Phys. Lett. 81, 4168 (2002); http://dx.doi.org/10.1063/1.1525880 (3 pages) | Cited 24 times

Online Publication Date: 19 November 2002

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We have used scanning white beam x-ray microdiffraction to study microstructural evolution during an in situ electromigration experiment on a passivated Al(Cu) test line. The data show plastic deformation and grain rotations occurring under the influence of electromigration, seen as broadening, movement, and splitting of reflections diffracted from individual metal grains. We believe this deformation is due to localized shear stresses that arise due to the inhomogeneous transfer of metal along the line. Deviatoric stress measurements show changes in the components of stress within the line, including relaxation of stress when current is removed. © 2002 American Institute of Physics.
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66.30.Qa Electromigration
85.40.Ls Metallization, contacts, interconnects; device isolation
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.05.cp X-ray diffraction
61.72.-y Defects and impurities in crystals; microstructure
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Suppression of silicidation in ZrO2/SiO2/Si structure by helium annealing

Kouichi Muraoka

Appl. Phys. Lett. 81, 4171 (2002); http://dx.doi.org/10.1063/1.1525393 (3 pages) | Cited 2 times

Online Publication Date: 19 November 2002

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Suppression of silicidation in ZrO2/SiO2/Si structure by high-temperature helium (He) gas annealing was demonstrated. Comparison of ultrahigh vacuum, 1 Torr N2 and He annealing with controlled oxygen partial pressure (PO2) at 920 °C revealed that the optimal PO2 range in He at which the thermal stability of the layered structure can be achieved is over one order wider than that in N2. This result suggests that He gas physically obstructs SiO removal through the quenching of atomic vibration and the occupation of SiO diffusion path in the ZrO2/SiO2 layer, thus impeding the contact of ZrO2, SiO, and Si effectively, which is the trigger of silicidation. Moreover, rapid thermal He annealing is found to be the most effective means of suppressing transition of interface structure. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.43.Mn Adsorption kinetics
61.72.Cc Kinetics of defect formation and annealing
68.60.Dv Thermal stability; thermal effects
68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films

Getting high-efficiency photoluminescence from Si nanocrystals in SiO2 matrix

Y. Q. Wang, G. L. Kong, W. D. Chen, H. W. Diao, C. Y. Chen, S. B. Zhang, and X. B. Liao

Appl. Phys. Lett. 81, 4174 (2002); http://dx.doi.org/10.1063/1.1525395 (3 pages) | Cited 40 times

Online Publication Date: 19 November 2002

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Silicon nanocrystals in SiO2 matrix are fabricated by plasma enhanced chemical vapor deposition followed by thermal annealing. The structure and photoluminescence (PL) of the resulting films is investigated as a function of deposition temperature. Drastic improvement of PL efficiency up to 12% is achieved when the deposition temperature is reduced from 250 °C to room temperature. Low-temperature deposition is found to result in a high quality final structure of the films in which the silicon nanocrystals are nearly strain-free, and the Si/SiO2 interface sharp. The demonstration of the superior structural and optical properties of the films represents an important step towards the development of silicon-based light emitters. © 2002 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Db Elemental semiconductors and insulators
61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Substrate-free crystallization of distorted hexagonal barium titanate thin films

N. Stavitski, V. Lyahovitskaya, J. Nair, I. Zon, R. Popovitz-Biro, E. Wachtel, Y. Feldman, and I. Lubomirsky

Appl. Phys. Lett. 81, 4177 (2002); http://dx.doi.org/10.1063/1.1524691 (3 pages) | Cited 7 times

Online Publication Date: 19 November 2002

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We show that substrate-free crystallized barium titanate (BaTiO3) films adopt a hexagonal structure, whereas substrate-supported films assume the commonly observed tetragonal phase. However, in contrast to the known hexagonal BaTiO3, the substrate-free crystallized films demonstrate a small but measurable pyroelectric effect, and do not exhibit phase transitions in the 25–423 K temperature range. Thus the substrate-free crystallized BaTiO3 represents a heretofore unreported crystallographic modification of BaTiO3. © 2002 American Institute of Physics.
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77.70.+a Pyroelectric and electrocaloric effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.55.-g Dielectric thin films

Porosity effect on the dielectric constant and thermomechanical properties of organosilicate films

Junjun Liu, Dongwen Gan, Chuan Hu, Michael Kiene, Paul S. Ho, Willi Volksen, and Robert D. Miller

Appl. Phys. Lett. 81, 4180 (2002); http://dx.doi.org/10.1063/1.1525054 (3 pages) | Cited 20 times

Online Publication Date: 19 November 2002

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This letter reports a study of the porosity effect on material properties of methylsilsesquioxane films, including the dielectric constant, thermal conductivity, and thermal stress behavior. In a porosity range from 0% to 50%, both the dielectric constant and thermal conductivity decreased with increasing porosity and no significant change was observed at the percolation point where pores became interconnected. In comparison, the stress–temperature slope also decreased with porosity, but as the porosity approached the percolation point, the slope showed a large drop of 40%, indicating a significant degradation of the thermomechanical properties due to percolation of pores. Assuming the coefficients of thermal expansion remain at 17 ppm/°C within the porosity range, the change in the stress–temperature slope corresponds to a decrease of the biaxial modulus from 7 to 5 GPa around the percolation point. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Jd Polymers; organic compounds
68.60.-p Physical properties of thin films, nonelectronic
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.40.De Thermal expansion; thermomechanical effects
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Interfacial oxide formation and oxygen diffusion in rare earth oxide–silicon epitaxial heterostructures

V. Narayanan, S. Guha, M. Copel, N. A. Bojarczuk, P. L. Flaitz, and M. Gribelyuk

Appl. Phys. Lett. 81, 4183 (2002); http://dx.doi.org/10.1063/1.1524692 (3 pages) | Cited 19 times

Online Publication Date: 19 November 2002

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We report on controlled interfacial oxide formation within epitaxial (LaxY1−x)2O3/Si(111) heterostructures under UHV environments. Results indicate that exposure of these epitaxial films to molecular oxygen right after deposition results in the formation of an amorphous interfacial layer thicker than that expected when a bare silicon surface is exposed to molecular oxygen under the same conditions. The results imply significant oxygen diffusion through the epitaxial dielectric and reaction at the silicon–oxide interface. Arguments have been developed to explain these observations. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Probing the AlxGa1−xN spatial alloy fluctuation via UV-photoluminescence and Raman at submicron scale

Leah Bergman, Xiang-Bai Chen, David McIlroy, and Robert F. Davis

Appl. Phys. Lett. 81, 4186 (2002); http://dx.doi.org/10.1063/1.1526918 (3 pages) | Cited 6 times

Online Publication Date: 19 November 2002

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We present a straightforward method for the study of alloy spatial compositional distribution at the submicron scale via photoluminescence and Raman spectroscopy. The spatial dependence of the band gap light-emission energy of AlxGa1−xN alloys at composition 0 ⩽ x ⩽ 1 was studied via deep UV-photoluminescence and Raman microscopy in order to address the issue of the spatial alloy fluctuation. The data were acquired in a random fashion from an area of ∼1 mm2 on the sample at steps of ∼1–200 μm utilizing the 244 nm laser line of probing spot size ∼300 nm radius. Our study indicates that the photoluminescence emission energy exhibits random type variations depending on locality: the alloys of composition x = 0.12, x = 0.22, x = 50, and x = 0.70 exhibit average variations of ∼10, 30, 45, and 25 meV, respectively. The photoluminescence of the pure GaN exhibits no significant spatial fluctuation. The stress contribution to the observed photoluminescence fluctuations was investigated via Raman analysis and was taken into account in order to estimate the local compositional fluctuation Δx. Our results indicate that for the higher Al composition alloys x = 0.50 and 0.70 the stress and the compositional fluctuation can be resolved, resulting in average spatial fluctuations of Δx = 0.004 and 0.002, respectively. © 2002 American Institute of Physics.
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61.66.Fn Inorganic compounds
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors

Electronic structure of the carbon nanotube tips studied by x-ray-absorption spectroscopy and scanning photoelectron microscopy

J. W. Chiou, C. L. Yueh, J. C. Jan, H. M. Tsai, W. F. Pong, I.-H. Hong, R. Klauser, M.-H. Tsai, Y. K. Chang, Y. Y. Chen, C. T. Wu, K. H. Chen, S. L. Wei, C. Y. Wen, L. C. Chen, et al.

Appl. Phys. Lett. 81, 4189 (2002); http://dx.doi.org/10.1063/1.1523152 (3 pages) | Cited 20 times

Online Publication Date: 19 November 2002

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Angle-dependent x-ray absorption near edge structure (XANES) and scanning photoelectron microscopy (SPEM) measurements have been performed to differentiate local electronic structures of the tips and sidewalls of highly aligned carbon nanotubes. The intensities of both π∗- and σ∗-band C K-edge XANES features are found to be significantly enhanced at the tip. SPEM results also show that the tips have a larger density of states and a higher C 1s binding energy than those of sidewalls. The increase of the tip XANES and SPEM intensities are quite uniform over an energy range wider than 10 eV in contrast to earlier finding that the enhancement is only near the Fermi level. © 2002 American Institute of Physics.
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73.22.Dj Single particle states
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
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