Chemistry, microstructure, and electrical properties at interfaces between thin films of cobalt and alpha (6H) silicon c
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J.S. Bow, M. J. Kim, and R.W. Carpenter Center for Solid State Science, Arizona State University, Tempe, Arizona 85287-1704 (Received 1 June 1994; accepted 27 September 1994)
Thin films (4-1000 A) of Co were deposited onto n-type 6H-SiC(0001) wafers by UHV electron beam evaporation. The chemistry, microstructure, and electrical properties were determined using x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and I-V and C-V measurements, respectively. The as-deposited contacts exhibited excellent rectifying behavior with low ideality factors and leakage currents of n < 1.06 and 2.0 X 10~8 A/cm 2 at - 1 0 V, respectively. During annealing at 1000 °C for 2 min, significant reaction occurred resulting in the formation of CoSi and graphite. These annealed contacts exhibited ohmic-like character, which is believed to be due to defects created in the interface region.
I. INTRODUCTION The extreme thermal, mechanical, and electronic properties of SiC make it an attractive material for use in both structural applications and high-power, hightemperature, high-speed, and high-frequency electronic and optoelectronic devices. The Co/SiC system has been studied by several investigators for the applications of both structural composites and contacts for devices.1"5 Because Ni is commonly employed as an ohmic contact to n-type 6H-SiC, 6 one also might expect ohmic behavior from annealed Co contacts when considering their chemical similarities and their similar work functions. The latter component of the Co/SiC research4'5 has shown Co to be a good rectifying contact on n-type 6H-SiC(0001) both in the as-deposited condition and after annealing at temperatures to 800 °C, while ohmiclike behavior was displayed after annealing at 900 °C. In this study, high resolution transmission electron microscopy (TEM) has been employed to investigate the interfacial chemistry and microstructure between Co and n-type 6H-SiC(0001) before and after annealing at 1000 °C. The results of these studies have been compared with other chemical studies and correlated with the electrical properties measured in the present research. II. EXPERIMENTAL Vicinal, single-crystal, nitrogen-doped, n-type (~ 1018 cm" 3 ) wafers of 1 in. diameter 6H-SiC(0001) containing 0.5-3.0/xm thick, n-type (~10 1 6 -10 1 7 cm~ 3 ) 26
J. Mater. Res., Vol. 10, No. 1, Jan 1995
http://journals.cambridge.org
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homoepitaxial films thermally oxidized to a thickness of 500-1000 A in dry oxygen at 1300 °C were provided by Cree Research, Inc. The epitaxial layers were unintentionally doped except where higher doping concentrations were needed; these latter films were intentionally doped with nitrogen during growth. The Si-terminated (0001) surface tilted 3°-4° toward [1120] was used for all depositions and analyses. The substrates were simultaneously cleaned and the oxide layer etched from the surface using a 10 min dip in a 10% hydrofluoric acid solution. This was followed by a quick rinse in de-ionized water. The substrates we
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