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  • 1
    Digitale Medien
    Digitale Medien
    Ta-based interface ohmic contacts to AlGaN/GaN heterostructures (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 5543-5546 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Al/Ti based metallization is commonly used for ohmic contacts to n-GaN and related compounds. We have previously reported an ohmic contact scheme specially designed for AlGaN/GaN heterostructure field-effect transistors (HFETs) [D. Qiao et al., Appl. Phys. Lett. 74, 2652 (1999)]. This scheme, referred to as the "advancing interface" contact, takes advantage of the interfacial reactions between the metal layers and the AlGaN barrier layer in the HFET structure. These reactions consume a portion of the barrier, thus facilitating carrier tunneling from the source/drain regions to the channel region. The advancing interface approach has led to consistently low contact resistance on Al0.25Ga0.75N/GaN HFETs. There are two drawbacks of the Al/Ti based advancing interface scheme, (i) it requires a capping layer for the ohmic formation annealing since Ti is too reactive and is easily oxidized when annealing is performed in pure N2 or even in forming gas, and (ii) the atomic number of Al and that of Ti are too low to yield efficient backscattered electron emission for e-beam lithographic alignment purposes. In this work, we investigated a Ta based advancing interface contact scheme for the HFET structures. We found that the presence of Ta in this ohmic scheme leads to (1) a specific contact resistivity as low as 5×10−7 Ω cm2, (2) efficient electron emission for e-beam lithographic alignment, and (3) elimination of the capping layer for the ohmic annealing. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1365431
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  • 2
    Digitale Medien
    Digitale Medien
    Dependence of Ni/AlGaN Schottky barrier height on Al mole fraction (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 801-804 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The dependence of the Schottky barrier height of Ni/AlxGa1−xN contact on the Al mole fraction up to x=0.23 was studied. The barrier heights were measured by I–V, capacitance–voltage, and the internal photoemission method. The Al mole fractions were estimated from the AlGaN band gap energies measured by photoluminescence. In the range of x〈0.2 a linear relationship between the barrier height and Al mole fraction was obtained. This was consistent with the slope predicted by the Schottky rule. For x=0.23, the measured barrier height was lower than predicted. We believed this was due to crystalline defects at the Ni/AlGaN interface. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371944
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  • 3
    Digitale Medien
    Digitale Medien
    Measurement of the Al mole fraction of bulk AlGaN and AlGaN/GaN heterostructure by photoconductance method (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2696-2699 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A photoconductance method was used to determine the band-gap energy and, therefore, the Al mole fraction of bulk AlxGa1−xN and AlxGa1−xN/GaN heterostructures. The results are compared with those obtained by a more elaborate photoluminescence method. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.371113
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  • 4
    Digitale Medien
    Digitale Medien
    A study of the Au/Ni ohmic contact on p-GaN (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 4196-4200 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The formation mechanism of the ohmic Au/Ni/p-GaN contact has been investigated. We found that it is essential to (i) deposit a structure of Au and Ni in the proper deposition sequence, and (ii) anneal the bilayer structure in an oxygen containing ambient. Our findings indicated that oxygen assists the layer-reversal reactions of the metallized layers to form a structure of NiO/Au/p-GaN. The presence of oxygen during annealing appears to increase the conductivity of the p-GaN. It is further suggested that Ni removes or reduces the surface contamination of the GaN sample before or during layer reversal. In the final contact structure, an Au layer, which has a large work function, is in contact with the p-GaN substrate. The presence of Au in the entire contacting layer improves the conductivity of the contact. An ohmic formation mechanism based on our experimental results is proposed and discussed in this work. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1311809
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  • 5
    Digitale Medien
    Digitale Medien
    The role of the tunneling component in the current–voltage characteristics of metal-GaN Schottky diodes (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 2099-2104 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The temperature dependence of the current–voltage characteristics of Ni–GaN Schottky barriers have been measured and analyzed. It was found that the enhanced tunneling component in the transport current of metal-GaN Schottky barrier contacts is a likely explanation for the large scatter in the measured Richardson constant. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.368270
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  • 6
    Digitale Medien
    Digitale Medien
    Study of Schottky barrier of Ni on p-GaN (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 4536-4538 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The Schottky barrier characteristics of Ni on p-GaN have been investigated using current–voltage–temperature (I–V–T) and capacitance–voltage characteristics (C–V) measurements. Barrier height values ranging from 2.68 to 2.87 eV were obtained from C–V measurements. The temperature dependence of I–V characteristics clearly indicated the dominance of tunneling current in the transport mechanism of the diodes, therefore, barrier height determination using I–V measurements can lead to erroneous results, as indicated by the wide range of barrier heights reported in the literature. Acceptor concentration, deduced from C–V measurements, was found to be of 1019/cm3 within 200 Å of the sample surface, and tapered off to be ∼1018/cm3. These values are 10–100 times higher than the hole concentration of ∼1017/cm3 obtained from Hall measurements. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1428773
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  • 7
    Digitale Medien
    Digitale Medien
    A simple reflectance method for estimation of the Al mole fraction of bulk AlGaN and AlGaN/GaN heterostructures (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 1419-1421 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In this study, we report a simple optical reflectance method to characterize the Al mole fraction in bulk AlGaN and AlGaN/GaN heterostructures. This method is based on the concept of Fabry–Perot oscillations of a probing beam when the photon energy of the beam falls below the band-gap energy of the semiconductor. The accuracy and merits of this method in comparison with the more elaborate photoluminescence method are discussed. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124712
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  • 8
    Digitale Medien
    Digitale Medien
    Ni and Ti Schottky barriers on n-AlGaN grown on SiC substrates (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 238-240 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The electrical characteristics of Ni and Ti Schottky barriers on n-Al0.15Ga0.85N on SiC were investigated. We report that the barrier height for Ni on n-Al0.15Ga0.85N was about 1.26 eV and about 1 eV or less for Ti. These barrier heights are about 0.3–0.4 eV larger than those for Ni and Ti on n-GaN, which are in good agreement with Schottky model predictions. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.121767
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  • 9
    Digitale Medien
    Digitale Medien
    Internal photoemission measurement of Schottky barrier height for Ni on AlGaN/GaN heterostructure (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 3917-3919 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The internal photoemission method was used to measure the Schottky barrier height of Ni on AlGaN/GaN heterostructures. A barrier height of 1.31 eV was found for the Ni/Al0.15Ga0.85N/GaN heterojunction structure, as compared to a barrier height of 1.28 and 1.02 eV for the Ni/Al0.15Ga0.85N and Ni/GaN Schottky diodes, respectively. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122935
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  • 10
    Digitale Medien
    Digitale Medien
    Schottky barrier engineering in III–V nitrides via the piezoelectric effect (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1880-1882 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A method for enhancing effective Schottky barrier heights in III–V nitride heterostructures based on the piezoelectric effect is proposed, demonstrated, and analyzed. Two-layer GaN/AlxGa1−xN barriers within heterostructure field-effect transistor epitaxial layer structures are shown to possess significantly larger effective barrier heights than those for AlxGa1−xN, and the influence of composition, doping, and layer thicknesses is assessed. A GaN/Al0.25Ga0.75N barrier structure optimized for heterojunction field-effect transistors is shown to yield a barrier height enhancement of 0.37 V over that for Al0.25Ga0.75N. Corresponding reductions in forward-bias current and reverse-bias leakage are observed in current–voltage measurements performed on Schottky diodes. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.122312
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