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15 May 2002

Volume 91, Issue 10, pp. 6227-8917

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Depth-dependent investigation of defects and impurity doping in GaN/sapphire using scanning electron microscopy and cathodoluminescence spectroscopy

X. L. Sun, S. H. Goss, L. J. Brillson, D. C. Look, and R. J. Molnar

J. Appl. Phys. 91, 6729 (2002); http://dx.doi.org/10.1063/1.1454187 (10 pages) | Cited 26 times

Online Publication Date: 13 May 2002

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Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from Al2O3 into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level at 3.447 meV near the interface for such samples, characteristic of O impurities spatially localized to the nanoscale interface. CLS emissions indicate the formation of amorphous Al–N–O complexes at 3.8 eV extending into the Al2O3 near the GaN/sapphire interface. CLS and CL images also reveal emissions due to excitons bound to stacking faults and cubic phase GaN. The temperature dependence of the various optical transitions in the 10–300 K range provides additional information to identify the near interface defects and impurity doping. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
78.66.Fd III-V semiconductors
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.72.Nn Stacking faults and other planar or extended defects
71.35.-y Excitons and related phenomena
82.80.Fk Electrochemical methods

Measurements of germanium K-shell ionization cross sections and tin L-shell x-ray production cross sections by electron impact

Changhuan Tang, Zhu An, Zhengming Luo, and Mantian Liu

J. Appl. Phys. 91, 6739 (2002); http://dx.doi.org/10.1063/1.1470248 (5 pages) | Cited 7 times

Online Publication Date: 13 May 2002

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This article reports experimental measurements of germanium K-shell ionization cross sections and tin L-shell x-ray production cross sections by electron impact. In order to avoid the difficulty of preparing thin and uniform self-supporting targets, thin targets with thick substrates are used in the experiments. Since electrons reflected by the substrate can induce additional ionization of target atoms, we developed a method to correct the measured x-ray intensities and eliminated the influence of the substrate on measured data. Our measured cross sections are in good agreement with previous measurements. The present results are also compared with the predictions of theories and semiempirical and empirical formulas. It is found that the K-shell ionization cross sections of Ge at energies from near threshold to 40 keV can be reasonably described by the semiempirical formula of Green and Cosslett. Experimental absolute L-shell x-ray production cross sections of Sn are presented. It seems that, so far, none of the available theories can adequately interpret our L-shell results at low energies. © 2002 American Institute of Physics.
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79.20.Hx Electron impact: secondary emission
34.80.Dp Atomic excitation and ionization

Evaluation of the coating–substrate adhesion by laser-ultrasonics: Modeling and experiments

Gaélle Rosa, Roland Oltra, and Marie-Hélène Nadal

J. Appl. Phys. 91, 6744 (2002); http://dx.doi.org/10.1063/1.1471579 (10 pages) | Cited 8 times

Online Publication Date: 13 May 2002

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The aim of the present study is to investigate a laser-ultrasonic method to determine the oxide-coating’s adhesion strength on a metallic substrate. In order to demonstrate this method a completely contactless system is used, combining laser generation and detection of ultrasonic waves. A nanosecond pulsed Nd:YAG laser is used to irradiate the transparent oxide coatings, while the normal displacement of the rear surface of the metallic substrate is detected at the epicenter by a laser heterodyne interferometer. Increasing the laser beam energy, the generated acoustic wave forms are correlated with the thermoelastic regime, the fracture of the coating–substrate interface, and finally the expulsion of the coating. The generation of ultrasonic signals in the thermoelastic regime is described by a two-dimensional model suitable to calculate the in- and out-of-plane components of the mechanical displacement versus time. The values of the so-called practical adhesion found are in agreement with those obtained by classic contact techniques (tensile adhesion test, indentation, bending test). This work demonstrates the suitability of this quantitative and contactless test to evaluate the coating–substrate adhesion. © 2002 American Institute of Physics.
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68.35.Np Adhesion
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect

Thermal oxidation of Si (001) single crystal implanted with Ge ions

A. Terrasi, S. Scalese, M. Re, E. Rimini, F. Iacona, V. Raineri, F. La Via, S. Colonna, and S. Mobilio

J. Appl. Phys. 91, 6754 (2002); http://dx.doi.org/10.1063/1.1471942 (7 pages) | Cited 5 times

Online Publication Date: 13 May 2002

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The thermal oxidation of Ge-implanted Si single crystals has been investigated for different Ge doses (3×1015 cm−2 and 3×1016 cm−2) and different oxidation processes (in wet ambient at 920 °C for 30, 60, and 120 min, or dry ambient at 1100 °C for 30 min). The oxide roughness, the oxidation rate, the Ge diffusion, precipitation, and clustering, have been monitored by several experimental techniques: atomic force microscopy, transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray absorption spectroscopy. We found that the surface roughness is related to the segregation of Ge at the oxide/substrate interface, occurring when the oxidation rate is faster than the Ge diffusion, in particular at the higher implanted dose (3×1016 cm−2) when processed in a wet ambient. For these conditions, we also observed an oxidation rate enhancement with respect to pure Si, and a strong indication that pure Ge clusters were formed. When a critical Ge concentration at the interface is reached, the oxidation mechanisms change and the oxidation rate is reduced, along with Ge diffusion into the substrate and a consequent reduction of the Ge fraction at the interface. Nevertheless, the oxide roughness still increases despite the Ge concentration reduction, resulting from the initial nucleation of precipitates. © 2002 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
61.72.uf Ge and Si
64.75.-g Phase equilibria
68.37.Ps Atomic force microscopy (AFM)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.70.Dm X-ray absorption spectra

Study of superalloy topography during ultrahigh intensity nanosecond ultraviolet laser ablation

Qihong Wu, Jiansheng Jie, Yurong Ma, Qingxuan Yu, Bin Miao, Guanzhong Wang, Yuan Liao, Rongchuan Fang, Xiangli Chen, and Kelvin Wang

J. Appl. Phys. 91, 6761 (2002); http://dx.doi.org/10.1063/1.1472239 (4 pages) | Cited 1 time

Online Publication Date: 13 May 2002

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We report on the topography of holes ablated by an ultrahigh intensity 355 and 266 nm laser with 8 ns pulse width in Ni-base superalloy Inconel 718. The origin of droplets, micropores, and microcracks on the surface of hole is identified. Qualitative differences in the characteristics of microcracks indicate that the dominant continuous microcracks result from thermal effects in 355 nm laser ablation, and the dominant island-chain microcrack result from photochemical effects in 266 nm laser ablation. In ultrahigh intensity laser ablation (>200 GW/cm2), the mechanical load on the surface is very significant to the resulting topography, and the grain boundary plays an important role in the origin of the micropores. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
52.38.Mf Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Bx Metals, semimetals, and alloys
61.82.Bg Metals and alloys
61.72.Mm Grain and twin boundaries

Structures, electrical properties, and equation of state in Ca4Mn3O10 under high pressure

R. C. Yu, G. W. Meng, L. C. Chen, Z. X. Bao, C. X. Liu, J. L. Zhu, F. Y. Li, Z. X. Liu, J. Liu, and C. Q. Jin

J. Appl. Phys. 91, 6765 (2002); http://dx.doi.org/10.1063/1.1473229 (4 pages) | Cited 3 times

Online Publication Date: 13 May 2002

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The structure changes and electrical properties in Ca4Mn3O10 under high pressure at room temperature have been studied using energy-dispersive x-ray diffraction with synchrotron radiation and resistance and capacitance measurements. A phase transition from an orthorhombic to a tetragonal phase occurred during increasing pressure to above 19.3 GPa. The equation of state of Ca4Mn3O10 was obtained from the V/V0–P relationship. The bulk modulus B0 and its first-order derivative B0′ of Ca4Mn3O10 were calculated based on the Birch–Murnaghan equation. © 2002 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
61.66.Fn Inorganic compounds
64.30.-t Equations of state of specific substances
72.80.Sk Insulators
64.70.K- Solid-solid transitions
62.20.D- Elasticity
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