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  • 1
    Publication Date: 2016-12-02
    Description: A new concept, Phase Segregation Annealing (PSA), was investigated for implementing simultaneous ohmic contacts (SOCs) to p - and n -type 4H-SiC. Test structures with selected ratio compositions of co-sputtered Pt:Ti contacts were fabricated in p -type 4H-SiC epitaxial layers having aluminum acceptor concentrations, N a  = 2 × 10 19 , 7 × 10 19 , and 2.5 × 10 20  cm −3 , and a nitrogen doped n -type epitaxial layer having donor concentration, N d  = 7 × 10 18  cm −3 . The ratios of the co-sputtered Pt-Ti metallization were 80:20, 50:50, and 30:70 at. %. After rapid thermal annealing (RTA) ranging between 800 and 1200 °C in vacuum and confirming SOCs by linear current-voltage (I-V) measurement, the specific contact resistance ( ρ c ) values were extracted using the Transfer Length Measurement method. SOCs were realized with the Pt80:Ti20 composition starting from 1000 °C, and the Pt30:Ti70 composition from 1100 °C, with both exhibiting eutectic and segregated phases. The Pt50:Ti50 composition produced no SOC and eutectic and segregated phases were absent. The Pt80:Ti20 composition had the lowest pair of average ρ c values of 7 × 10 −5 Ω cm 2 and 7.3 × 10 −4 Ω cm 2 on the highest doped p -type and the n -type samples after RTA at 1000 °C, respectively. Auger electron spectroscopy and focused ion beam field emission scanning electron microscopy with energy dispersive x-ray spectroscopy indicated distinct phase segregation via the eutectic-liquidus-eutectic transitions, the coalescence of likely Pt 3 Si and Pt 2 Si binary phases, and solid phases of Ti 3 Si, Ti 5 Si 3 , and TiC, with all the active phases maintaining intimate contact to both the p - and n -type 4H-SiC surfaces. The SOC formation was attributed to the disparate work functions of these phases, which was in good agreement with the proposed PSA model.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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