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, Na = 2 × 1019, 7 × 1019, and 2.5 × 1020 cm−3, and a nitrogen doped n-type epitaxial layer having donor concentration, Nd = 7 × 1018 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 (ρc) 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 ρc values of 7 × 10−5 Ω cm2 and 7.3 × 10−4 Ω cm2 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 Pt3Si and Pt2Si binary phases, and solid phases of Ti3Si, Ti5Si3, 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.
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7 December 2016
Research Article|
December 01 2016
Simultaneous ohmic contacts to p- and n-type 4H-SiC by phase segregation annealing of co-sputtered Pt-Ti
R. S. Okojie
;
R. S. Okojie
1
NASA Glenn Research Center
, 21000 Brookpark Road, Cleveland, Ohio 44135, USA
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D. Lukco
D. Lukco
2Vantage Partners,
LLC
, 21000 Brookpark Road, Cleveland, Ohio 44135, USA
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J. Appl. Phys. 120, 215301 (2016)
Article history
Received:
September 18 2016
Accepted:
November 10 2016
Citation
R. S. Okojie, D. Lukco; Simultaneous ohmic contacts to p- and n-type 4H-SiC by phase segregation annealing of co-sputtered Pt-Ti. J. Appl. Phys. 7 December 2016; 120 (21): 215301. https://doi.org/10.1063/1.4968572
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