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  • 1
    Electronic Resource
    Electronic Resource
    Influence of buffer layers on the deposition of high quality single crystal GaN over sapphire substrates (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4700-4702 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently several research groups, including ours, have reported on the deposition of extremely high quality single crystal GaN layers over sapphire substrates. One of the keys to obtaining the high quality was the use of a thin AlN or GaN buffer layer between the sapphire substrate and the grown film. In this communication, we discuss the crystallinity and the influence of the buffer layer in controlling the crystalline, optical, and the electrical properties of the GaN depositions. We also compare the use of GaN and AlN as the buffer layer material. Our results indicate that the buffer layer thickness and the total film thickness are the key factors controlling the electrical, optical, and crystalline properties of the GaN depositions over sapphire substrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354069
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  • 2
    Electronic Resource
    Electronic Resource
    Free excitonic transitions in GaN, grown by metal-organic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7001-7004 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic processes of the free excitonic transitions in GaN grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. The recombination lifetimes of the A and B excitons have been measured at different temperatures and excitation intensities, from which radiative recombination lifetimes of about 0.35 and 0.3 ns for the A and B excitons, respectively, have been obtained. An increase in excitation power has resulted in a drastic enhancement in the radiative decay rate as well as in the exciton photoluminescence quantum yield, suggesting the excitonic transitions may provide gain for laser actions in GaN. The high quality as well as high purity of the investigated MOCVD sample has been demonstrated by the observations of (1) the free A- and B-excitonic transitions, (2) excited states of the free excitons, (3) narrow free excitonic emission linewidths (1.7 meV at 10 K), (4) low electron concentration, and (5) high electron mobilities (∼600 cm2/V s). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362448
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  • 3
    Electronic Resource
    Electronic Resource
    Infrared reflectance of AlN–GaN short period superlattice films (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2372-2377 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The room-temperature infrared reflectance of AlN–GaN short period superlattice films has been measured. These superlattice films were deposited by switched atomic layer metalorganic chemical vapor deposition onto GaN or AlN buffer layers deposited on basal plane sapphire substrates. The measured reflectance spectra are compared to calculated spectra using an effective medium theory to model the dielectric function of the superlattice. The optical properties of the individual materials making up the samples are modeled with Lorentz oscillators using only bulk input parameters. The effects of film and substrate anisotropy and off-normal incidence are included in the calculation. Using this modeling technique, it is possible to obtain thickness estimates for the superlattice film and the buffer layer. The complicated structures seen in the reststrahl region reflectance of these films are also analyzed by comparison to the calculated spectra. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363072
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  • 4
    Electronic Resource
    Electronic Resource
    High electron mobility GaN/AlxGa1−xN heterostructures grown by low-pressure metalorganic chemical vapor deposition (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 2408-2410 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter we report the first observation of enhanced electron mobility in GaN/AlxGa1−xN heterojunctions. These structures were deposited on basal plane sapphire using low-pressure metalorganic chemical vapor deposition. The electron mobility of a single heterojunction composed of 500 A(ring) of Al0.09Ga0.91N deposited onto 0.3 μm of GaN was around 620 cm2/V s at room temperature as compared to 56 cm2/V s for bulk GaN of the same thickness deposited under identical conditions. The mobility for the single heterojunction increased to a value of 1600 cm2/V s at 77 K whereas the mobility of the 0.3 μm GaN layer alone peaked at 62 cm2/V s at 180 K and decreased to 19 cm2/V s at 77 K. A 18-layer multiple heterojunction structure displayed a peak mobility of 1980 cm2/V s at 77 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104886
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  • 5
    Electronic Resource
    Electronic Resource
    Vertical-cavity, room-temperature stimulated emission from photopumped GaN films deposited over sapphire substrates using low-pressure metalorganic chemical vapor deposition (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1515-1517 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first observation of near-UV vertical-cavity stimulated emission from a photopumped GaN epilayer at room temperature. The epilayer was deposited over AIN-coated basal plane sapphire substrate using low-pressure metalorganic chemical vapor deposition. Epitaxy quality of a 1.5-μm-thick GaN layer was high enough to achieve stimulated emission at room temperature. The observed near-UV optical emission power was a nonlinear function of the pump power density. At threshold power density, we also observed line narrowing and a shift of the peak UV emission towards longer wavelengths. Data comparing the UV emission for the vertical-cavity and the edge emission geometry are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105163
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  • 6
    Electronic Resource
    Electronic Resource
    Electron transport in AlGaN–GaN heterostructures grown on 6H–SiC substrates (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 707-709 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated two-dimensional electron transport in doped AlGaN–GaN heterostructures (with the electron sheet concentration ns(approximate)1013 cm−2) grown on conducting 6H–SiC substrates in the temperature range T=0.3–300 K. The electron mobility in AlGaN–GaN heterostructures grown on SiC was higher than in those on sapphire substrates, especially at cryogenic temperatures. The highest measured Hall mobility at room temperature was μH=2019 cm2/V s. At low temperatures, the electron mobility increased approximately five times and saturated below 10 K at μH=10250 cm2/V s. The experimental results are compared with the electron mobility calculations accounting for various electron scattering mechanisms. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120852
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  • 7
    Electronic Resource
    Electronic Resource
    InGaN-GaN based light-emitting diodes over (111) spinel substrates (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 369-370 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this letter we report the deposition of high quality GaN-InGaN double-heterostructure pn junctions over (111) spinel substrates using low-pressure metalorganic chemical vapor deposition. A ten-period undoped GaN-In0.1Ga0.9N multiple quantum well was used for the active region. Mesa-type light-emitting diode (LED) structures were fabricated which under forward bias exhibited only strong band-edge electroluminescence. The spectral emission was centered at 385 nm and had a linewidth of 15 nm. This is similar to what is measured for similar LED structures over sapphire substrates. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.118063
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  • 8
    Electronic Resource
    Electronic Resource
    Metastability and persistent photoconductivity in Mg-doped p-type GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1808-1810 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical properties of Mg-doped p-type GaN grown by metalorganic chemical vapor deposition have been investigated by Hall effect and conductivity measurements. Metastability and persistent photoconductivity effects have been observed in GaN. It was found that at low temperatures, it takes several hours for the free hole concentration to reach its equilibrium value in the dark as well as in the photoexcited state, implying a bistable nature of impurities in p-type GaN. Temperature dependence of these behaviors have been studied, from which the energy barrier for free hole capture by ionized impurities as well as between the metastable and the stable states of neutral impurities have been obtained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116020
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  • 9
    Electronic Resource
    Electronic Resource
    Observation of optically detected magnetic resonance in GaN films (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 2673-2675 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optically detected magnetic resonance has been observed from GaN. Two magnetic resonances have been detected on the 2.2 eV-deep photoluminescence band. The first resonance is sharp [full width at half-maximum (FWHM) ∼2.2 mT] with g(parallel)=1.9515±0.0002 and g⊥=1.9485±0.0002 and is assigned to conduction electrons, in agreement with recent electron paramagnetic resonance (EPR) studies of similar samples. The second feature, which has not been seen by EPR, is much broader (FWHM∼13 mT) with g(parallel)=1.989±0.001 and g⊥=1.992±0.001. These parameters indicate a deep state. A tentative assignment is made to a deep state associated with the N vacancy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110416
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  • 10
    Electronic Resource
    Electronic Resource
    High-responsivity photoconductive ultraviolet sensors based on insulating single-crystal GaN epilayers (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2917-2919 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the fabrication and characterization of photoconductive ultraviolet detectors based on insulating single-crystal GaN. The active layer (GaN) was deposited over basal-plane sapphire substrates using a unique switched atomic-layer-epitaxy process. The sensors were measured to have a responsivity of 2000 A/W at a wavelength of 365 nm under a 5-V bias. The responsivity remained nearly constant for wavelengths from 200 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 375 nm). We estimate our sensors to have a gain of 6×103 (for wavelength 365 nm) and a bandwidth in excess of 2 kHz. The photosignal exhibited a linear behavior over five orders of incident optical power, thereby implying a very large dynamic range for these GaN-based ultraviolet sensors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106819
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