12 November 1999 High-temperature performance of ohmic contacts to n-type GaN and GaAs
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Cu3Ge was studied as an Ohmic contact to n-GaN and n- type GaAs. Specific contact resistance of Cu3Ge to n- type GaAs was found to be sensitive to annealing conditions, doping concentrations, and Ge compositions. After vacuum annealing at 400 degree(s)C for 30 min, Cu3Ge exhibited ohmic behavior to n-type GaN with doping concentrations of approximately 1.0 X 1018 cm-3. Unprotected Cu3Ge ohmic contacts suffered from oxidation when exposed at temperatures higher than 300 degree(s)C. Aging tests at 400 degree(s)C where Cu3Ge covered with TiW and Au was used as ohmic contact to n-type GaAs, and TiPtAu covered with Au to p-type GaAs, revealed unchanged I-V characteristics after 120 hr annealing which showed that this contact was suitable for device application at high temperature. Pseudomorphic HEMT employing protected Cu3Ge ohmic contacts and Ti/Pt/Au gates has achieved peak transconductance of 330 mS/mm at room temperature for 2- micrometers long gate. The I-V characteristic of Pd/Al, covered with TiW/Pt changed from Ohmic to Schottky after aging at 350 degree(s)C for 2 hours. By depositing a very thin Cr layer between Ti/Al and Au layers, contact resistance of Ti/Al contacts remained the same even after an aging of 130 hr at 350 degree(s)C and 130 hr at 400 degree(s)C. However, specific contact resistance increased from 2.4 X 10-6 (Omega) cm2 to 3.8 X 10-6 (Omega) cm2 after annealing at 500 degree(s)C for 2 hr.
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Jehn-Huar Howard Chern, Jehn-Huar Howard Chern, R. Jennifer Hwu, R. Jennifer Hwu, Laurence P. Sadwick, Laurence P. Sadwick, } "High-temperature performance of ohmic contacts to n-type GaN and GaAs", Proc. SPIE 3795, Terahertz and Gigahertz Photonics, (12 November 1999); doi: 10.1117/12.370168; https://doi.org/10.1117/12.370168


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