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  • 1
    Electronic Resource
    Electronic Resource
    Stimulated Raman backscattering with and without optical fiber smoothing technique in 0.53 μm laser-created plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2075-2083 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Backward stimulated Raman scattering (SRS) experiments have been performed using the optical fiber smoothing implemented on the high-power Phébus laser facility [Laser Part. Beams 4, 93 (1988)]. The interaction took place in low-Z plasmas presenting either exponential density profiles (solid targets) or Gaussian-type profiles. Raman instability was driven with 1.4 ns duration—0.53 μm laser pulses, containing an energy up to 1.8 kJ. Comparative and absolute measurements of SRS reflectivity are reported as a function of the incident laser intensity, both with and without beam smoothing. Near-backward time-resolved SRS spectra are also presented. Random phase plates are not used in these experiments. With or without smoothing, SRS reflectivities of the order of 10% have been measured. However, smoothing becomes effective in exponential profiles below 1015 W/cm2. Although the optical fiber efficiently reduces the contrast of the energy modulations in the focal spot, the spectral bandwidth may be insufficient to quench SRS development in these conditions. This last assumption is in agreement with theoretical predictions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871294
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  • 2
    Electronic Resource
    Electronic Resource
    All-in-one spectrometer—A simple experimental setup for measuring transport characteristics in semiconductors (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 4985-4988 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The characterization of semiconductor heterostructures requires different measurement techniques such as photoluminescence, Shubnikov–de Haas, and cyclotron resonance. We present a simple experimental setup which allows to make use of all these techniques without changing the equipment. There is no need for electrical contacts. The performance is demonstrated on InxGa1−xAs/InP quantum wells. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146120
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  • 3
    Electronic Resource
    Electronic Resource
    Photoluminescence study of the 1.047 eV emission in GaN (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3214-3218 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use photoluminescence to study residual transition metal contaminants in GaN layers, which are grown by the sandwich technique either on 6H-SiC substrate or on sapphire substrate. We observe three no-phonon lines in the near infrared optical region at 1.3 eV, 1.19 eV, and 1.047 eV caused by 3d transition metals. The appearance of GaN related host modes in the phonon sideband of these emissions proves that the luminescence centers are incorporated in the hexagonal GaN layers. In this paper we especially focus on the luminescence band with the no-phonon line at 1.047 eV. Temperature dependent photoluminescence measurements reveal an excited state splitting of 8 meV. In photoluminescence excitation spectroscopy we observe a further excited state at 1.6 eV with a fine structure splitting. The appearance of this excited state in the n-type samples gives evidence that the defect must already exist in its luminescent charge state without illumination. The experimental results on the 1.047 eV emission fit to a 4T2(F)→4A2(F) internal electronic transition of a transition metal with a 3d7 electronic configuration. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361266
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  • 4
    Electronic Resource
    Electronic Resource
    Dispersion relation, electron and hole effective masses in InxGa1−xAs single quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1481-1485 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on optical and electrical properties of modulation doped InxGa1−xAs/InP single quantum wells in the composition range 0.56≤x≤0.79. Cyclotron resonance, contactless Shubnikov–de Haas and magnetophotoluminescence experiments are used to obtain two dimensional carrier densities, effective masses of electrons and holes and scattering times. We present data which give evidence for zero magnetic field spin splitting. The dispersion relation for electrons and holes is presented. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360988
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  • 5
    Electronic Resource
    Electronic Resource
    Optical investigations of AlGaN on GaN epitaxial films (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 2456-2458 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated coherently strained AlxGa1−xN/GaN heterostructures (0〈x〈0.22) grown by metalorganic vapor phase epitaxy on sapphire with photoluminescence (PL), reflexion and cathodoluminescence experiments. The energetic positions of the free A exciton as a function of the alloy compositions are deduced from temperature dependent PL and from reflexion measurements. We obtain a small bowing parameter and no evidence for a Stokes shift between absorption and emission. Compositional inhomogeneities are present, but the fluctuations are too small to be important for carrier localization. The broadening of the luminescence linewidth in the alloys can be described by statistical disorder of a random alloy. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123879
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  • 6
    Electronic Resource
    Electronic Resource
    Properties of GaN grown at high rates on sapphire and on 6H–SiC (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2716-2718 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thick GaN films were deposited with growth rates as high as 250 μm/h by the direct reaction of ammonia and gallium vapor at 1240 °C. The characteristics of our films are comparable to those of typical thin films grown by metal organic chemical vapor deposition or molecular beam epitaxy. Grown under identical conditions, films on (0001) sapphire and on (0001) 6H–SiC were compared in terms of their structural and optical properties. Considering x-ray rocking curve full width at half-maximum (FWHM: 420 arcsec), photoluminescence linewidths of the excitons (FWHM: 3 meV at 6 K and 100 meV at 300 K), free electron concentration, defect related luminescence, and the homogeneity of these properties, we find superior values for films grown on SiC. For both substrate materials we find an optimum growth rate window of 40–80 μm/h. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117688
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  • 7
    Electronic Resource
    Electronic Resource
    Spatially resolved photoluminescence and Raman scattering experiments on the GaN/substrate interface (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1265-1266 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results from spatially resolved photoluminescence and Raman experiments on the substrate interface region of wurtzite GaN layers. We show that the broad photoluminescence band with an intensity maximum at 2.4 eV is not an intrinsic property of GaN. We found that this photoluminescence band is strong only near the interface. Our investigations reveal that both the substrate interface and a region of structural reorientation of the layer near the interface act as a source of the photoluminescence. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115947
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  • 8
    Electronic Resource
    Electronic Resource
    Structural investigations of GaN grown by low-pressure chemical vapor deposition on 6H–SiC and Al2O3 from GaCl3 and NH3 (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 1890-1895 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN films grown on (0001) 6H–SiC and (0001) Al2O3 substrates using low-pressure chemical vapor deposition with GaCl3 and NH3 as precursors are comparatively explored by optical, scanning tunneling, and transmission electron microscopy. Independent of the substrate material used, the surface of the GaN layers is covered by hexagonally shaped islands. For GaN on 6H–SiC, the islands are larger in diameter ((approximate)50 μm) and rather uniformly distributed. An atomically flat interface is observed for GaN on Al2O3 in contrast to GaN grown on 6H–SiC, where the interface is characterized by large steps. For both substrates, faceted holes (named as pinholes) are observed in near-surface regions of the GaN layers occurring with a density of about 7×108 cm−2. No unequivocal correlation between the density of pinholes and the density of threading dislocations ((approximate)1.6×1010 cm−2 for GaN/Al2O3 and (approximate)4×109 cm−2 for GaN/6H–SiC) can be found. Rather, different types of defects are identified to be correlated with the pinholes, implying a dislocation-independent mechanism for the pinhole formation. Despite the small lattice mismatch between GaN and 6H–SiC, the pronounced original surface roughness of this substrate material is believed to account for both the marked interfacial roughness and the still existing high density of threading dislocations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365994
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  • 9
    Electronic Resource
    Electronic Resource
    Damage induced by plasma etching: On the correlation of results from photoluminescence and transport characterization techniques (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1403-1405 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma dry etching, used for the fabrication of low-dimensional structures, is known to create defects in the material which affect both the optical and the transport properties of the sample. We compare the results obtained from three different methods of characterizing the damage induced by electron cyclotron resonance metalorganic reactive ion etching to the two-dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures: photoluminescence, transport measurements, and electron paramagnetic resonance. Etching impairs the quality of luminescence and decreases the single-particle relaxation time, while the concentration of a surface related paramagnetic defect (probably dangling bonds) is increased. However, detailed experiments show no correlation between the density of defects and transport or luminescence properties, nor between transport and luminescence properties. In particular, hydrogen passivation, which improves the luminescence properties after etching, leads to deteriorated transport properties. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113215
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature dependent electrically detected magnetic resonance studies on silicon pn diodes (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1521-1523 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on electrically detected magnetic resonance (EDMR) studies in silicon pn diodes in the temperature range from 30 to 300 K. In the range from 150 to 300 K the resonance effect is, as usually observed, much larger than expected by spin polarization. From 150 K down to 30 K the spin resonance effect increases by a factor of 25, which is attributed to spin polarization of free electrons and electrons bound to recombination centers. Our investigation suggests that at least two different mechanisms contribute to the EDMR signal. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113633
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