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  • 1
    Electronic Resource
    Electronic Resource
    Microstructure of GaN laterally overgrown by metalorganic chemical vapor deposition (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 747-749 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extended defect reduction in GaN grown by lateral epitaxial overgrowth (LEO) on large-area SiO2/GaN/Al2O3 wafers by low pressure metalorganic chemical vapor deposition is characterized using transmission electron microscopy and atomic force microscopy. The laterally overgrown GaN (LEO GaN) has a rectangular cross section with smooth (0001) and {112¯0} facets. The density of mixed-character and pure edge threading dislocations in the LEO GaN (〈5×106 cm−2) is reduced by at least 3–4 orders of magnitude from that of bulk GaN (∼1010 cm−2). A small number of edge dislocations with line directions parallel to the basal plane are generated between the bulk-like overgrown GaN and the LEO GaN regions as well as at the intersection of adjacent merging LEO GaN stripes. The edge dislocations are most likely generated to accommodate the small misorientation between bulk-like GaN and LEO GaN regions as well as between adjacent single-crystal LEO GaN stripes. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121988
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  • 2
    Electronic Resource
    Electronic Resource
    Metalorganic chemical vapor deposition of high mobility AlGaN/GaN heterostructures (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5850-5857 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, we discuss parameters influencing (a) the properties of thin AlxGa1−xN layers grown by metalorganic chemical vapor deposition and (b) the electrical properties of the two-dimensional electron gas (2DEG) forming at the AlxGa1−xN/GaN heterojunction. For xAl〉0.3, the AlxGa1−xN layers showed a strong tendency towards defect formation and transition into an island growth mode. Atomically smooth, coherently strained AlxGa1−xN layers were obtained under conditions that ensured a high surface mobility of adsorbed metal species during growth. The electron mobility of the 2DEG formed at the AlxGa1−xN/GaN interface strongly decreased with increasing aluminum mole fraction in the AlxGa1−xN layer and increasing interface roughness, as evaluated by atomic force microscopy of the surfaces prior to AlxGa1−xN deposition. In the case of modulation doped structures (GaN/AlxGa1−xN/AlxGa1−xN:Si/AlxGa1−xN), the electron mobility decreased with decreasing thickness of the undoped spacer layer and increasing silicon doping. The electron mobility was only moderately affected by the dislocation density in the films and independent of the growth temperature of the AlxGa1−xN layers at xAl=0.3. For Al0.3Ga0.7N/GaN heterojunctions, electron mobility values up to 1650 and 4400 cm2/V s were measured at 300 and 15 K, respectively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371602
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  • 3
    Electronic Resource
    Electronic Resource
    Dislocation mediated surface morphology of GaN (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6470-6476 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surfaces of GaN films grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were studied using atomic force microscopy (AFM). Due to the high dislocation densities in the films (108 cm−2), the typical surface morphologies of layers grown by both techniques were dominated by three dislocation mediated surface structures—pinned steps, spiral hillocks, and surface depressions. The characteristics of these surface structures were found to depend on growth technique (MOCVD vs MBE) and the group-III to group-V ratio used in the growth of MBE GaN films. Pinned steps, created by the intersections of mixed character dislocations with the free surface, were found on all GaN films. The pinned steps were observed to be predominantly straight on the MOCVD GaN and curved into spiral hillock formations on the MBE GaN. Spiral growth hillocks form when pinned steps grow outward and around the dislocation under step-flow growth conditions. The tightness of the spiral hillocks on MBE GaN surfaces was found to increases with III/V ratio. Surface depressions, caused by the high strain-energy density near dislocations, were also observed on the surfaces of the GaN films. Two characteristic depression sizes were found on all MOCVD GaN films whereas depressions were observed only on MBE GaN films grown with low III/V ratios. These observations are explained using theories developed by Burton, Cabrera, and Frank [Philos. Trans. R. Soc. London, Ser. A 243, 299 (1951)] and Frank [Acta Crystallogr. 4, 497 (1951)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370150
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  • 4
    Electronic Resource
    Electronic Resource
    Effects of growth conditions on the incorporation of oxygen in AlGaN layers grown by plasma assisted molecular beam epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3167-3169 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using secondary ion mass spectroscopy we have shown that oxygen incorporation in AlGaN films is dependent upon the III/V growth conditions and the growth temperature of the films. AlGaN films grown under excess group III conditions (Ga-rich) exhibited step flow growth and at least a factor of 3 less oxygen incorporation than films grown under excess group V (N-rich conditions). We found that oxygen incorporation into AlGaN decreases as the growth temperature is increased. The lowest oxygen levels were achieved by growing at 750 °C under Ga-rich growth conditions. Possible sources of unwanted oxygen are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1325398
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  • 5
    Electronic Resource
    Electronic Resource
    Two-dimensional electron-gas AlN/GaN heterostructures with extremely thin AlN barriers (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3998-4000 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma-assisted molecular-beam epitaxy is used to grow a set of two-dimensional electron-gas AlN/GaN structures with AlN barrier thicknesses varied between 24 and 50 Å. The density of the two-dimensional electron gas formed at the GaN/AlN interface increases from 1.51×1013 cm−2 for the AlN barrier width of 24 Å to 3.65×1013 cm−2 for the AlN barrier width of 49 Å. The increase in the electron sheet density is accompanied by a decrease in electron mobility related to tensile strain relaxation and enhanced interface roughness scattering. It is shown that room-temperature sheet resistances below 200 Ω/(square, open) can be achieved in AlN/GaN high electron mobility transistor structures with 35–45 Å AlN barriers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1332408
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  • 6
    Electronic Resource
    Electronic Resource
    Mg doping of GaN layers grown by plasma-assisted molecular-beam epitaxy (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 718-720 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN:Mg layers grown by plasma-assisted molecular-beam epitaxy at 650 °C are investigated. Secondary-ion-mass-spectroscopy measurements reveal uniform Mg doping profiles with very sharp boundaries. The amount of incorporated Mg atoms changes approximately linearly with incident Mg flux. Hall measurements on p-type GaN:Mg layers show that about 1%–2% of all Mg atoms are ionized at room temperature. The hole mobility depends strongly on the hole concentration, varying from μp=24 cm2/V s for p=1.8×1017 cm−3 to μp=7.5 cm2/V s for p=1.4×1018 cm−3. GaN p–n diodes with molecular-beam-epitaxy-grown p regions are analyzed using current–voltage measurements. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.125872
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  • 7
    Electronic Resource
    Electronic Resource
    High-performance (Al,Ga)N-based solar-blind ultraviolet p–i–n detectors on laterally epitaxially overgrown GaN (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 247-249 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Solar-blind ultraviolet photodiodes with a band-edge wavelength of 285 nm were fabricated on laterally epitaxially overgrown GaN grown by metalorganic chemical vapor deposition. Current–voltage measurements of the diodes exhibited dark current densities as low as 10 nA/cm2 at −5 V. Spectral response measurements revealed peak responsivities of up to 0.05 A/W. Response times for these diodes were measured to be as low as 4.5 ns for 90%-to-10% fall time. For comparison, diodes were fabricated using the same p–i–n structure deposited on dislocated GaN. These diodes had dark current densities many orders of magnitude higher, as well as a less sharp cutoff, and a significant slow tail under impulse excitation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124337
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  • 8
    Electronic Resource
    Electronic Resource
    High-quality coalescence of laterally overgrown GaN stripes on GaN/sapphire seed layers (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1706-1708 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have characterized GaN stripes grown by lateral epitaxial overgrowth on large-area (2 in.) SiO2/GaN/Al2O3 wafers by low-pressure metalorganic chemical vapor deposition before and after coalescence. Using scanning electron microscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscope (AFM), it is shown that by first obtaining "wings" (laterally overgrown material) with low tilt relative to the "seed" (underlying) GaN, very few extended defects are formed when wings from neighboring stripes coalesce. After wings with a tilt of ∼0.1° are coalesced and an additional ∼10 μm of GaN is grown, it is found with XRD that peak splitting due to tilt is no longer detectable. TEM and AFM results show that few dislocations (with a linear density 〈4×103 cm−1) are formed at coalescence fronts. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124796
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  • 9
    Electronic Resource
    Electronic Resource
    Polarization effects, surface states, and the source of electrons in AlGaN/GaN heterostructure field effect transistors (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 250-252 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The origin of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructure field effect transistors is examined theoretically and experimentally. Based on an analysis of the electrostatics, surface states are identified as an important source of electrons. The role of the polarization-induced dipole is also clarified. Experimental Hall data for nominally undoped Al0.34Ga0.66N/GaN structures indicate that ∼1.65 eV surface donors are the actual source of the electrons in the 2DEG, which forms only when the barrier thickness exceeds 35 Å. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126940
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  • 10
    Electronic Resource
    Electronic Resource
    In situ, real-time measurement of wing tilt during lateral epitaxial overgrowth of GaN (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3893-3895 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By performing in situ, real-time x-ray diffraction measurements in the metalorganic chemical-vapor deposition environment, we have directly observed the emergence and evolution of wing tilt that occurs during the lateral overgrowth of GaN from stripes patterned in a SiO2 mask. This was done by repeatedly performing line scans through the 101¯3 peak in the direction perpendicular to the [101¯0]GaN stripe direction. The wing tilt developed as soon as the wings started forming, and increased slightly thereafter to reach a value of ∼1.19° after 3600 s of growth. Upon cooldown to room temperature, the tilt increased to ∼1.36°, indicating that thermally induced stresses during cooldown have only a small effect on wing tilt. However, changes in mask density, composition, and stress state during early lateral overgrowth must be considered as possible origins of wing tilt. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126812
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