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  • 1
    Electronic Resource
    Electronic Resource
    On the incorporation of Mg and the role of oxygen, silicon, and hydrogen in GaN prepared by reactive molecular beam epitaxy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 219-226 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mg-doped GaN samples prepared by reactive molecular beam epitaxy have been investigated in an attempt to gain insight into the impurity incorporation and the origin of auto doping in otherwise undoped GaN films. The Hall and secondary ion mass spectroscopy data were utilized for the analysis of possible background impurities such as Si, O, and H in an effort to ascertain whether the background electron concentration is of impurity origin or native defect origin. The data appear to support the N vacancy as a possible cause of auto-n-type doping seen in undoped GaN. The effect of the ammonia flow rate on the incorporation of Mg atoms in GaN films and on the behavior of H were studied for layers grown on c-plane sapphire as well as 6H–SiC. Increased incorporation of Mg with larger ammonia flow rates is attributed to Ga vacancies and accompanying site selection. Moreover, p-GaN films grown under high ammonia flux are reported with a hole concentration, mobility, and resistivity of about 8×1017 cm−3, 26 cm2/V s, and 0.3 Ω cm, respectively. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365801
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  • 2
    Electronic Resource
    Electronic Resource
    Electrical conduction in platinum–gallium nitride Schottky diodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4467-4478 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gallium nitride is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Among the devices considered for high power generation is the ubiquitous field-effect transistors which require Schottky barriers for modulating the channel mobile charge. It is in this context that we have undertaken an investigation of likely metal-GaN contacts. Here we report on the electrical conduction and other properties of Pt–GaN Schottky diodes. These Schottky diodes were fabricated using n-GaN grown by the molecular beam epitaxy method. Both capacitance–voltage and current–voltage measurements have been carried out as a function of temperature to gain insight into the processes involved in current conduction. Based on these measurements, physical mechanisms responsible for electrical conduction at low and high voltages and temperatures have been suggested. Schottky barrier height determined from the current–voltage and capacitance–voltage measurements is close to 1.10 eV. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363408
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  • 3
    Electronic Resource
    Electronic Resource
    Reactive molecular beam epitaxy of wurtzite GaN: Materials characteristics and growth kinetics (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7657-7666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High quality GaN layer growth by reactive molecular beam epitaxy employing ammonia gas as a nitrogen source and with high growth rates (∼2 μm/h) is described. The high crystalline quality of the layer is evidenced by our recently reported modulation-doped field-effect transistors, GaN/AlGaN separate confinement heterostructures, GaN/AlGaN quantum wells, high quality Schottky contacts, long excitonic lifetime, and GaN epitaxial layers that exhibit only intrinsic transitions even with the second excited states of excitonic transitions visible in the emission spectra. The dependence of background carrier concentration and resistivity on substrate temperature is studied. The hexagonal nature of wurtzite GaN manifests itself as hexagonal features on the film, becoming as large as ∼5 μm with facets at high growth temperatures (e.g., 800 °C). For low V/III ratios, large hexagonal hillocks, with highly strained regions on them, are formed due to the localized preferential growth. The photoluminescence characteristics of the films grown with various V/III ratios are also studied. The PL spectra were analyzed to uncover the effect of substrate temperature on the crystalline quality, as well as on electrical and optical properties of films. The ground and excited state excitons were seen from the layer grown at 800 °C with a growth rate of 1.2 μm/h. The influence of two competing factors, viz., thermal activation of ammonia and thermal desorption of Ga from the surface, on the growth kinetics was investigated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362430
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  • 4
    Electronic Resource
    Electronic Resource
    Mg-doped p-type GaN grown by reactive molecular beam epitaxy (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 559-561 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: P-type conductivity in as-grown Mg-doped GaN films grown by reactive molecular beam epitaxy technique which employs ammonia as the nitrogen source is reported. Doping level and mobility of the films up to 4.5×1017 cm−3 and 6 cm2/V s, respectively, have been achieved without any post-growth treatments. The photoluminescence spectra show both band edge and Mg-related emission at room temperature. Neither annealing in nitrogen ambient furnace nor rapid thermal annealing was found to have any discernible influence on the electrical properties of the films. More than 6% of incorporated Mg was activated for the samples with relatively low Mg concentration. The measured activation energy of Mg acceptor was 160±5 meV. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117786
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  • 5
    Electronic Resource
    Electronic Resource
    Suppression of leakage currents and their effect on the electrical performance of AlGaN/GaN modulation doped field-effect transistors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1229-1231 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical characteristics of high performance of AlGaN/GaN modulation doped field-effect transistors (MODFETs) grown by reactive molecular beam epitaxy method are studied experimentally. The maximum measured drain-source current is 490 mA/mm, which saturates at a relatively low drain-source voltage VDS. The transconductance increases with decreasing gate length reaching a value of 186 mS/mm in devices with a gate length of LG=2 μm. Breakdown voltages of about 90 V have also been exhibited by devices with gate length LG=2 μm and drain-gate separation LDG=1 μm. To our knowledge, these are the best values obtained so far from GaN MODFETs which we attribute to the suppression of leakage currents and improved materials structure of the devices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117420
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts for n-GaN (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1556-1558 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy has been applied to characterize the structure of Ti/Al and Ti/Al/Ni/Au Ohmic contacts on n-type GaN (∼1017 cm−3) epitaxial layers. The metals were deposited either by conventional electron-beam or thermal evaporation techniques, and then thermally annealed at 900 °C for 30 s in a N2 atmosphere. Before metal deposition, the GaN surface was treated by reactive ion etching. A thin polycrystalline cubic TiN layer epitaxially matched to the (0001) GaN surface was detected at the interface with the GaN substrate. This layer was studied in detail by electron diffraction and high resolution electron microscopy. The orientation relationship between the cubic TiN and the GaN was found to be: {111}TiN//{00.1}GaN, [110]TiN//[11.0]GaN, [112]TiN//[10.0]GaN. The formation of this cubic TiN layer results in an excess of N vacancies in the GaN close to the interface which is considered to be the reason for the low resistance of the contact. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117060
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  • 7
    Electronic Resource
    Electronic Resource
    Photoluminescence characterization of the quantum well structure and influence of optical illumination on the electrical performance of AlGaN/GaN modulation-doped field-effect transistors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 1420-1422 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrical characteristics of high performance GaN modulation-doped field-effect transistors (MODFETs) grown by reactive molecular beam epitaxy method are studied experimentally both in dark and under white light illumination. The maximum measured drain-source current is 626 mA/mm in dark and 695 mA/mm under illumination, which saturates at a relatively low drain-source voltage VDS. The transconductance increases with decreasing gate length reaching a value of 210 mS/mm in dark and 222 mS/mm under illumination for devices with a gate length of LG=1.5μm. Breakdown voltages of about 90 V have also been exhibited by devices with gate length LG=1.5 μm and drain-gate distance LDG=1 μm. To our knowledge, these are the best values obtained so far from GaN MODFETs which we attribute to the suppression of leakage currents and improved materials structure of the devices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117601
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of buffer layer and substrate surface polarity on the growth by molecular beam epitaxy of GaN on ZnO (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3111-3113 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present results on the effect of substrate surface polarity, oxygen and zinc faces, on the quality of GaN epitaxial layers grown on ZnO(0001) substrates by reactive ammonia molecular beam epitaxy. The possible effects dealing with the disparity in surface preparation of the two faces have been eliminated. Photoluminescence and reflectivity measurements demonstrate that the oxygen face leads to higher quality GaN on ZnO compared to the zinc face. We also present optical data obtained by using different low-temperature AlN, GaN, and InxGa1−xN buffer layers. The best result has been obtained with lattice-matched In0.20Ga0.80N buffer layer. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.120262
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  • 9
    Electronic Resource
    Electronic Resource
    High temperature characteristics of AlGaN/GaN modulation doped field-effect transistors (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 3872-3874 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current–voltage characteristics of AlGaN/GaN modulation doped field-effect transistors at elevated temperatures are studied experimentally. The drain–source current and extrinsic transconductance are both found to decrease with increasing temperature. Decrease in mobility with increasing temperatures is considered to be one of the causes of the reduction in the current and transconductance. The capacitance–voltage characteristic reveals the absence of heat activated traps in the modulation doped layer. The physics underlying various high-temperature operations of current–voltage characteristics is discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117133
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