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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Metalorganic chemical vapor deposition of GaN on Si(111): Stress control and application to field-effect transistors (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7846-7851 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two schemes of nucleation and growth of gallium nitride on Si(111) substrates are investigated and the structural and electrical properties of the resulting films are reported. Gallium nitride films grown using a 10–500 nm-thick AlN buffer layer deposited at high temperature (∼1050 °C) are found to be under 260–530 MPa of tensile stress and exhibit cracking, the origin of which is discussed. The threading dislocation density in these films increases with increasing AlN thickness, covering a range of 1.1 to 〉5.8×109 cm−2. Films grown using a thick, AlN-to-GaN graded buffer layer are found to be under compressive stress and are completely crack free. Heterojunction field effect transistors fabricated on such films result in well-defined saturation and pinch-off behavior with a saturated current of ∼525 mA/mm and a transconductance of ∼100 mS/mm in dc operation. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1372160
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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
    Defect structure of metal-organic chemical vapor deposition-grown epitaxial (0001) GaN/Al2O3 (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3228-3237 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Defect structures were investigated by transmission electron microscopy for GaN/Al2O3 (0001) epilayers grown by metal-organic chemical vapor deposition using a two-step process. The defect structures, including threading dislocations, partial dislocation bounding stacking faults, and inversion domains, were analyzed by diffraction contrast, high-resolution imaging, and convergent beam diffraction. GaN film growth was initiated at 600 °C with a nominal 20 nm nucleation layer. This was followed by high-temperature growth at 1080 °C. The near-interfacial region of the films consists of a mixture of cubic and hexagonal GaN, which is characterized by a high density of stacking faults bounded by Shockley and Frank partial dislocations. The near-interfacial region shows a high density of inversion domains. Above ∼0.5 μm thickness, the film consists of isolated threading dislocations of either pure edge, mixed, or pure screw character with a total density of ∼7×108 cm−2. The threading dislocation reduction in these films is associated with cubic to hexagonal transformation of the nucleation layer region during high temperature growth. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363264
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  • 5
    Electronic Resource
    Electronic Resource
    Indium tin oxide contacts to gallium nitride optoelectronic devices (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3930-3932 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated GaN-based light-emitting diodes using transparent indium tin oxide (ITO) p contacts. ITO-contacted devices required an additional 2 V to drive 10 mA, as compared to similar devices with metal contacts. However, ITO has lower optical absorption at 420 nm (α=664 cm−1) than commonly used thin metal films (α=3×105 cm−1). Uniform luminescence was observed in ITO-contacted devices, indicating effective hole injection and current spreading. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.124227
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  • 6
    Electronic Resource
    Electronic Resource
    Emission mechanisms of bulk GaN and InGaN quantum wells prepared by lateral epitaxial overgrowth (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1460-1462 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The emission mechanisms of bulk GaN and InGaN quantum wells (QWs) were studied by comparing their optical properties as a function of threading dislocation (TD) density, which was controlled by lateral epitaxial overgrowth. Slightly improved excitonic photoluminescence (PL) intensity was recognized by reducing TD density from 1010 cm−2 to less than 106 cm−2. However, the major PL decay time was independent of the TD density, but was rather sensitive to the interface quality or material purity. These results suggest that TDs simply reduce the net volume of light-emitting area. This effect is less pronounced in InGaN QWs where carriers are effectively localized at certain quantum disk size potential minima to form quantized excitons before being trapped in nonradiative pathways, resulting in a slow decay time. The absence of any change in the optical properties due to reduction of TD density suggested that the effective band gap fluctuation in InGaN QWs is not related to TDs. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.123581
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Structural origin of V-defects and correlation with localized excitonic centers in InGaN/GaN multiple quantum wells (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 692-694 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the growth of InGaN/GaN multiple quantum well (MQW) structures, a novel defect (called the "V-defect") initiates at threading dislocations in one of the first quantum wells in a MQW stack. This defect is common to almost all InGaN MQW heterostructures. The nature of the V-defect was evaluated using transmission electron microscopy (TEM), scanning TEM (STEM), and low-temperature cathodoluminescence (CL) on a series of In0.20Ga0.80N/GaN MQW samples. The structure of the V-defect includes buried side-wall quantum wells (on the {101¯1} planes) and an open hexagonal inverted pyramid which is defined by the six {101¯1} planes. Thus, in cross section this defect appears as an open "V". The formation of the V-defect is kinetically controlled by reduced Ga incorporation on the pyramid walls ({101¯1} planes). The V-defect is correlated with the localized excitonic recombination centers that give rise to a long-wavelength shoulder in photoluminescence (PL) and CL spectra. This long-wavelength shoulder has the following characteristics: (i) its intensity is correlated with the side-wall quantum wells; (ii) the temperature independence of the full width at half maximum strongly supports a localized exciton recombination process. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120844
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  • 9
    Electronic Resource
    Electronic Resource
    Very high breakdown voltage and large transconductance realized on GaN heterojunction field effect transistors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1438-1440 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report record high breakdown voltages up to 340 and 230 V realized on unintentionally doped (1.5 μm gate length) and Si doped (1 μm gate length) AlGaN/GaN modulation doped field effect transistors (MODFETs), respectively. The devices also have large transconductances up to 140 mS/mm and a full channel current of 150–400 mA/mm. The Si doped MODFET sample demonstrated a very high room temperature mobility of 1500 cm2/Vs. With these specifications, GaN field effect transistors as microwave power devices are practical. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117607
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  • 10
    Electronic Resource
    Electronic Resource
    Radiative recombination lifetime measurements of InGaN single quantum well (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1936-1938 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results from a time-resolved study of radiative recombination in InGaN quantum wells. The sample was grown by atmospheric pressure metal-organic chemical-vapor deposition. Time-resolved photoluminescence measurements were performed from 7 K up to room temperature. The low temperature radiative lifetime was measured to be on the order of 250 ps at a generated carrier density of 1012 cm−2. The time-resolved measurements show a bimolecular recombination characteristic. At 300 K, we observed a lifetime of 130 ps which, to the best of our knowledge, is the longest lifetime reported for any III–V nitride at room temperature. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117627
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