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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of exposure and processing of thick PMMA for deep x-ray lithography using hard x-rays (1998)
    Springer
    Microsystem technologies 4 (1998), S. 86-88 
    Details
    ISSN: 1432-1858
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Technology
    Notes: Abstract  The first step for the fabrication of microstructures using deep x-ray lithography (DXRL) is the radiation of a sensitive polymer like poly(methyl methacrylate) (PMMA) by hard x-ray. At the Advanced Photon Source a dedicated beamline1 allowed the proper exposure of very thick resist (several mm). In this work we give a characterization of the PMMA/development system. As a result the resist dissolution rate (μm/min) of the exposed PMMA in different developer is calculated. We also analyze the conditions that produce bubbles and cracks in the thick exposed resist and investigate the scanning parameters that reduce them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005420050102
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  • 2
    Electronic Resource
    Electronic Resource
    Laser action in GaN pyramids grown on (111) silicon by selective lateral overgrowth (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2242-2244 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser action was observed in GaN pyramids under strong optical pumping at room temperature. The pyramids were laterally overgrown on a patterned GaN/AlN seeding layer grown on a (111) silicon substrate by metal–organic chemical vapor deposition. Each pyramid had a 15-μm-wide hexagonal base and was on average 15 μm in height. The pyramids were individually pumped, imaged, and spectrally analyzed through a high-magnification telescope system using a high-density pulsed excitation source. Under high levels of optical pumping, multimode laser at room temperature was observed. The integrated emission intensity for both spontaneous and lasing peaks was studied as a function of excitation power density. The effects of pyramid geometry and short-pulse excitation on the multimode nature of laser oscillations inside of the pyramids is discussed. This study suggests that GaN microstructures could potentially be used as pixel elements and high-density two-dimensional laser arrays. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121689
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  • 3
    Electronic Resource
    Electronic Resource
    Erratum: "Recombination dynamics in n-AlxGa1−xAs/n-In0.5Ga0.5P type-II heterostructures" [Appl. Phys. Lett. 73, 1245 (1998)] (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2219-2219 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122431
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  • 4
    Electronic Resource
    Electronic Resource
    Pump-probe spectroscopy of band tail states in metalorganic chemical vapor deposition-grown InGaN (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1892-1894 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanosecond nondegenerate optical pump-probe experiments have been performed on InGaN thin films and InGaN/GaN multiple quantum wells. Bleaching of absorption of the localized band tail states was observed with increasing excitation density (Iexc) of the pump pulse. The dynamics of the bleaching was found to depend on the localization depth of the band tail states and on Iexc. With high Iexc, large blueshifts in the spontaneous emission luminescence peaks were also observed, the magnitude of which was again found to depend on the localization depth of the band tail states. Stimulated emission is observed from the samples with increasing Iexc and correlates with significant changes in the behavior of the absorption bleaching. The observed bleaching dynamics of the band tail states are well explained by considering the effective lifetime of the band tail states as measured by time-resolved photoluminescence experiments. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122317
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  • 5
    Electronic Resource
    Electronic Resource
    "S-shaped" temperature-dependent emission shift and carrier dynamics in InGaN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1370-1372 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report temperature-dependent time-integrated and time-resolved photoluminescence (PL) studies of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. We observed anomalous emission behavior, specifically an S-shaped (decrease–increase–decrease) temperature dependence of the peak energy (Ep) for InGaN-related PL with increasing temperature: Ep redshifts in the temperature range of 10–70 K, blueshifts for 70–150 K, and redshifts again for 150–300 K with increasing temperature. In addition, when Ep redshifts, the spectral width is observed to narrow, while when Ep blueshifts, it broadens. From a study of the integrated PL intensity as a function of temperature, it is found that thermionic emission of photocarriers out of local potential minima into higher energy states within the wells is the dominant mechanism leading to the thermal quenching of the InGaN-related PL. We demonstrate that the temperature-induced S-shaped PL shift is caused by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the InGaN/GaN MQWs. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122164
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  • 6
    Electronic Resource
    Electronic Resource
    Optical properties of wurtzite GaN grown by low-pressure metalorganic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3691-3696 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present the results of optical studies on the properties of GaN grown by low-pressure metalorganic chemical-vapor deposition, with emphasis on the issues vital to device applications such as stimulated emission and laser action as well as carrier relaxation dynamics. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. Using a picosecond streak camera, the free and bound exciton emission decay times were examined. In addition, the effects of temperature and pressure on the optical interband transitions and the transitions associated with impurity/defect states were studied using a variety of spectroscopic methods, including photoluminescence and photoreflectance. The fundamental band gap of GaN was mapped out as a function of temperature using the empirical Varshni relation. The pressure coefficient of the gap was determined using diamond-anvil pressure-cell technique. The hydrostatic deformation potential for the direct Γ band gap was also derived from the experimental results. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361200
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 3158-3160 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results of a time-resolved photoluminescence study of the dynamics of photoexcited carriers in AlxGa1−xN/GaN double heterostructures (DHs). The carrier dynamics including generation, diffusion, spontaneous recombination, and nonradiative relaxation were studied by examining the time decay of photoluminescence associated with the spontaneous recombination from the samples. The temporal evolution of the luminescence from the GaN active layers of the DH samples was found to be governed by a carrier–diffusion dominated capture process. The determination of the capture time for the carriers drift and diffusion into the GaN active region, in addition to the effective lifetimes of the spontaneous recombination for carriers in the AlGaN cladding layers and the GaN active region, allows an estimation of the diffusion constants for the minority carriers in the AlxGa1−xN cladding layers of the DHs. Our results yield a diffusion constant of 2.6 cm2/s for Al0.03Ga0.97N and 1.5 cm2/s for Al0.1Ga0.9N at 10 K. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366101
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  • 8
    Electronic Resource
    Electronic Resource
    High resolution x-ray analysis of pseudomorphic InGaN/GaN multiple quantum wells: Influence of Si doping concentration (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 3006-3008 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the structural properties of InGaN/GaN/AlGaN multiple quantum wells (MQWs) by means of two-dimensional reciprocal space mapping (RSM) of high resolution x-ray diffraction. The influence of Si doping in GaN barriers on the characteristics has been studied for 12-period MQWs grown by metalorganic chemical vapor deposition, which have different Si doping concentrations in the GaN barriers ranging from 1×1017 to 3×1019 cm−3. Information on the structural quality of these MQWs was extracted from the linewidth broadening of the higher-order superlattice satellite peaks, as well as from the presence of Pendellösung oscillations. The measured diffraction curves were modeled using kinematic diffraction theory. From the symmetric and asymmetric RSMs around (0002), (0004) and (112¯4) reflections, we found that the InGaN/GaN/AlGaN MQWs are grown coherently on the GaN base layer. Better interface properties are achieved with Si doping. Our results indicate that Si doping in the GaN barriers affects the interface quality of the InGaN/GaN MQW systems, and thus, also influences the optical properties. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369620
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  • 9
    Electronic Resource
    Electronic Resource
    Stimulated emission in GaN thin films in the temperature range of 300–700 K (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1792-1795 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of an experimental study on stimulated and spontaneous emission from high-quality single-crystal GaN films grown on 6H-SiC and (0001) sapphire substrates in the temperature range of 300–700 K. We observed edge-emitted stimulated emission (SE) at temperatures as high as 700 K for samples grown on both SiC and sapphire substrates. The energy position of the SE and spontaneous emission peaks were shown to shift linearly to longer wavelengths with temperature and empirical expressions for the energy positions are given. We demonstrate that the energy separation between the spontaneous and SE peaks gradually increases from 90 meV at 300 K to 200 meV at 700 K indicating that an electron-hole plasma is responsible for the SE mechanism in this temperature range. The temperature sensitivity of the SE threshold for different samples was studied and the characteristic temperature was found to be 173 K in the temperature range of 300–700 K for one of the samples studied. We suggest that the unique properties of SE in GaN thin films at high temperatures could potentially be utilized in optoelectronic devices. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369325
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  • 10
    Electronic Resource
    Electronic Resource
    Room-temperature deep-ultraviolet-stimulated emission from AlxGa1−xN thin films grown on sapphire (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 245-247 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature deep-ultraviolet-stimulated emission (SE) has been observed from optically pumped metalorganic chemical vapor deposition grown AlxGa1−xN thin films. SE has been observed for Al concentrations as high as x=0.26, with a resultant SE wavelength as low as 328 nm at room temperature. The results obtained for the AlxGa1−xN layers are compared with InxGa1−xN layers of comparable alloy concentration and GaN reference layers. The incorporation of Al into GaN is shown to result in AlxGa1−xN layers with similar high excitation-density emission behavior as GaN, in contrast to InxGa1−xN layers, which exhibit markedly different SE behavior. The observation of room-temperature SE from AlxGa1−xN layers of significant Al concentration illustrates the suitability of AlxGa1−xN based structures, not only for use in deep-ultraviolet detectors, but also as a potential source of deep-ultraviolet laser radiation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123269
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