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  • 1
    Electronic Resource
    Electronic Resource
    Blistering of H-implanted GaN (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 3928-3930 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanisms of blistering of wurtzite GaN films implanted with H ions are studied. In particular, we report on the influence of the following parameters on the blistering process: (i) ion energy (from 20 to 150 keV), (ii) ion dose (up to 1.2×1018 cm−2), (iii) implantation temperature (from −196 to 250 °C), and (iv) annealing temperature (up to 900 °C). Results show that both the onset of blistering and blistering surface patterns strongly depend on implant conditions. This study may have significant technological implications for ion slicing and "etching" of GaN using high-dose implantation with H ions. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1430533
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  • 2
    Electronic Resource
    Electronic Resource
    Polycrystallization and surface erosion of amorphous GaN during elevated temperature ion bombardment (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 5493-5495 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of elevated-temperature ion bombardment of wurtzite GaN films preamorphized by ion implantation are studied by Rutherford backscattering/channeling spectrometry and transmission electron microscopy. Amorphous layers annealed in vacuum at 500 °C exhibit polycrystallization. Bombardment of amorphous layers with 2 MeV 63Cu+ ions at elevated temperatures leads to anomalous erosion of GaN (with a sputtering yield of ∼102 at 500 °C), rather than to ion-beam-induced epitaxial crystallization. Temperature dependence of the erosion rate suggests that such a large sputtering yield results from a two-step process of (i) thermally- and ion- beam-induced material decomposition and (ii) ion beam erosion of a highly N-deficient near-surface layer of GaN. This study shows that amorphization during ion implantation should be avoided due to the present inability to epitaxially recrystallize amorphous layers in GaN. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1318361
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  • 3
    Electronic Resource
    Electronic Resource
    Mössbauer spectroscopic studies of the moment distribution in Fe73.5Cu1Nb3Si13.5B9 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 7106-7108 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 57Fe Mössbauer spectroscopy can be used to determine the distribution of moment directions in magnetic materials. Here, we have applied this technique to a study of Fe73.5Cu1Nb3Si13.5B9 (isocompositional with FINEMET). We are particularly interested in establishing the distribution of moment directions in the nanophase material, obtained by devitrification from an amorphous precursor. The nanophase material consists of Fe–Si grains embedded in an amorphous matrix. Current understanding of the resulting magnetic properties, which involves application of the random anisotropy model to these materials, assumes that the magnetization in the grains is exchange coupled to neighbors, giving a long exchange length compared with the nanometer grain size. We present data for the amorphous precursor, the standard nanophase material, and nanophase material devitrified in an external magnetic field. If σu and σv represent the Gaussian widths of the out-of-plane and in-plane moment direction distributions respectively, we have found that σu=14° and σv=68° for the amorphous precursor, σu=14° and σv=92° for the standard nanophase material, and σu=22° and σv=79° for a magnetic field aligned specimen. We interpret these data as demonstrating that standard devitrification does result in grains with a wide spread of moment direct ions over the volume sampled by this technique, even allowing for exchange coupling. These results and the implications for macroscopic magnetic properties such as anisotropy will be discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372945
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  • 4
    Electronic Resource
    Electronic Resource
    Mechanical deformation of single-crystal ZnO (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 956-958 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The deformation behavior of bulk ZnO single crystals is studied by a combination of spherical nanoindentation and atomic force microscopy. Results show that ZnO exhibits plastic deformation for relatively low loads ((approximately-greater-than)4–13 mN with an ∼4.2 μm radius spherical indenter). Interestingly, the elastic–plastic deformation transition threshold depends on the loading rate, with faster loading resulting, on average, in larger threshold values. Multiple discontinuities (so called "pop-in" events) in force–displacement curves are observed during indentation loading. No discontinuities are observed on unloading. Slip is identified as the major mode of plastic deformation in ZnO, and pop-in events are attributed to the initiation of slip. An analysis of partial load–unload data reveals values of the hardness and Young's modulus of 5.0±0.1 and 111.2±4.7 GPa, respectively, for a plastic penetration depth of 300 nm. Physical processes determining deformation behavior of ZnO are discussed. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1448175
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  • 5
    Electronic Resource
    Electronic Resource
    Implantation-produced structural damage in InxGa1−xN (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 602-604 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of In content on the accumulation of structural damage in InxGa1−xN films (with x=0.0–0.2) under heavy-ion bombardment is studied by a combination of Rutherford backscattering/channeling spectrometry and transmission electron microscopy. Results show that an increase in In concentration strongly suppresses dynamic annealing processes and, hence, enhances the buildup of stable lattice disorder in InGaN under ion bombardment, A comparison of the damage buildup behavior and defect microstructure in InGaN with those in GaN is presented. Results of this study may have significant technological implications for estimation and control of implantation-produced damage in InGaN/GaN heterostructures. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388881
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  • 6
    Electronic Resource
    Electronic Resource
    Electrical isolation of GaN by MeV ion irradiation (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 943-945 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The evolution of sheet resistance of n-type GaN epilayers exposed to irradiation with MeV H, Li, C, and O ions is studied in situ. Results show that the threshold dose necessary for complete isolation linearly depends on the original free electron concentration and reciprocally depends on the number of atomic displacements produced by ion irradiation. Furthermore, such isolation is stable to rapid thermal annealing at temperatures up to 900 °C. In addition to providing a better understanding of the physical mechanisms responsible for electrical isolation, these results can be used for choosing implant conditions necessary for an effective electrical isolation of GaN-based devices. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1348306
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  • 7
    Electronic Resource
    Electronic Resource
    Structural disorder in ion-implanted AlxGa1−xN (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 787-789 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The accumulation of structural damage in AlxGa1−xN films (with x=0.05–0.60) under heavy-ion bombardment at room temperature is studied by a combination of Rutherford backscattering/channeling spectrometry and cross-sectional transmission electron microscopy (XTEM). Results show that an increase in Al concentration strongly enhances dynamic annealing processes in AlGaN and suppresses ion-beam-induced amorphization. All AlGaN wafers studied show damage saturation in the bulk for high ion doses. Interestingly, the disorder level in the saturation regime is essentially independent of Al content. In contrast to the case of GaN, no preferential surface disordering is observed in AlGaN during heavy-ion bombardment. XTEM reveals similar implantation-produced defect structures in both GaN and AlGaN. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1445478
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  • 8
    Electronic Resource
    Electronic Resource
    Indentation-induced damage in GaN epilayers (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 80 (2002), S. 383-385 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable "footprint" of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the samples studied for loads of up to 250 mN. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1436280
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  • 9
    Electronic Resource
    Electronic Resource
    Direct observation of voids in the vacancy excess region of ion bombarded silicon (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2867-2869 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results reported in this letter indicate that the spatial separation of the vacancy and interstitial excesses which result from ion bombardment gives rise to stable voids upon annealing at 850 °C even for implants where the projected ion range is only of the order of a few thousand A(ring)ngstrom. Such voids have been observed directly by transmission electron microscopy. Furthermore, in cases where both voids and interstitial-based defects are present at different depths, it is found that Au has a strong preference for decorating void surfaces and hence Au can, indeed, be used as a selective detector of open volume defects in Si. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1352662
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  • 10
    Electronic Resource
    Electronic Resource
    Terahertz-frequency electronic coupling in vertically coupled quantum dots (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 4356-4358 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied terahertz absorption of samples containing two layers of self-aligned, self-assembled InAs quantum dots separated by a thin GaAs barrier. The vertically coupled dots were charged with electrons by applying a voltage bias between a metal gate and a doped layer beneath the dots. For a positive gate bias corresponding to flatband conditions, an absorption peak was observed near 10 meV (2.4 THz). The absorption is attributed to the inhomogeneously broadened transition between the quantum mechanically split levels (bonding and antibonding states) in the vertically coupled quantum dots. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1334912
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