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

L. L. Smith, R. F. Davis, R. J. Liu, M. J. Kim, Ray Carpenter

Research output: Contribution to journalArticle

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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 × 10-5 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 × 10-6 Ω cm2; for n = 4.5 × 1017 cm-3, ρc = 7.5 × 10-5 Ω cm2 after annealing both samples through 900 (Service mark)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.

Original languageEnglish (US)
Pages (from-to)1032-1038
Number of pages7
JournalJournal of Materials Research
Volume14
Issue number3
StatePublished - Mar 1999

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Ohmic contacts
electric contacts
Electric properties
Thermodynamic stability
thermal stability
electrical properties
Annealing
Transmission electron microscopy
microstructure
Microstructure
Carrier concentration
Electric lines
X ray photoelectron spectroscopy
electrical resistivity
Single crystals
Thin films
transmission electron microscopy
annealing
high resistance
transmission lines

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN. / Smith, L. L.; Davis, R. F.; Liu, R. J.; Kim, M. J.; Carpenter, Ray.

In: Journal of Materials Research, Vol. 14, No. 3, 03.1999, p. 1032-1038.

Research output: Contribution to journalArticle

Smith, L. L. ; Davis, R. F. ; Liu, R. J. ; Kim, M. J. ; Carpenter, Ray. / Microstructure, electrical properties, and thermal stability of Ti-based ohmic contacts to n-GaN. In: Journal of Materials Research. 1999 ; Vol. 14, No. 3. pp. 1032-1038.
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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 × 10-5 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 × 10-6 Ω cm2; for n = 4.5 × 1017 cm-3, ρc = 7.5 × 10-5 Ω cm2 after annealing both samples through 900 (Service mark)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.",
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