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Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN

Published online by Cambridge University Press:  31 January 2011

L. L. Smith ,
R. F. Davis ,
R-J. Liu ,
M. J. Kim  and
R. W. Carpenter
L. L. Smith
Affiliation:
Materials Research Center, North Carolina State University, Raleigh, North Carolina 27695-7919
R. F. Davis
Affiliation:
Materials Research Center, North Carolina State University, Raleigh, North Carolina 27695-7919
R-J. Liu
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704
M. J. Kim
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704
R. W. Carpenter
Affiliation:
Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704
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Abstract

Single Ti layers, single TiN layers, and thin Ti films overlayered with Au were investigated as ohmic contacts to n-type (n 4.5 × 1017 to 7.4 × 1018 cm−3) single-crystal GaN (0001) films. Transmission line measurements (TLM) revealed the as-deposited TiN and Au/Ti contacts on n = 1.2 − 1018 cm−3 to be ohmic with room-temperature specific contact resistivities of 650 and 2.5 × 107minus;5 Ω cm2, respectively. Single Ti layer contacts had high resistance and were weakly rectifying in the as-deposited condition. The three contact/GaN systems exhibited a substantial decrease in resistivity after annealing; the value of ρc was also a function of the carrier concentration in the GaN. The Au/Ti contacts exhibited the lowest resistivity values yet observed in these contact studies, particularly for the more lightly doped n-GaN. The ρc for n = 1.2 × 1018 cm−3 reached 1.2 × 1026 Ω cm2; for n = 4.5 × 1017 cm−3, ρc = 7.5 × 1025 Ω cm2 after annealing both samples through 900 °C. X-ray photoelectron spectroscopy (XPS) and high-resolution cross-sectional transmission electron microscopy (X-TEM) analysis revealed the formation of TiN at the interface of annealed Ti layers in contact with GaN, which is believed to be beneficial for ohmic contact performance on n-GaN.

Type
Articles
Information
Journal of Materials Research , Volume 14 , Issue 3 , March 1999 , pp. 1032 - 1038
Copyright
Copyright © Materials Research Society 1999

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