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

Published online by Cambridge University Press:  31 January 2011

L. L. Smith ,
R. F. Davis ,
M. J. Kim ,
R. W. Carpenter  and
Y. Huang
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
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
Y. Huang
Affiliation:
Argonne National Laboratory, Argonne, Illinois 60439
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Abstract

As-deposited Al contacts were ohmic with a room-temperature contact resistivity of 8.6 × 10−5 Ω · cm2 on Ge-doped, highly n-type GaN (n = 5 × 1019 cm−3). They remained thermally stable to at least 500 °C, under flowing N2 at atmospheric pressure. The specific contact resistivities (ρc) calculated from TLM measurements on as-deposited Al layers were found to range from 8.6 × 10−5 Ω · cm2 at room temperature and 6.2 × 10−5 Ω · cm2 at 500 °C. Annealing treatments at 550 °C and 650 °C for 60 s each under flowing N2 resulted in an overall increase of contact resistivity. Cross-sectional, high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during high-temperature treatments, and coincided with the degradation of contact performance. Electron diffraction patterns from the particles revealed a cubic structure with lattice constant a = 0.784 nm, and faceting occurring on the {100} faces. Spectroscopic analysis via electron energy loss spectroscopy (EELS) revealed the presence of nitrogen and small amounts of oxygen in the Al layer, but no appreciable amounts of Ga. The results of microstructural and crystallographic characterization indicate that the new interfacial phase is a type of spinel Al nitride or Al oxynitride.

Type
Articles
Information
Journal of Materials Research , Volume 11 , Issue 9 , September 1996 , pp. 2257 - 2262
Copyright
Copyright © Materials Research Society 1996

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