Electrical and microstructural investigation of Au/Pd/ri ohmic contacts for AIGaAs/GaAs heterojunction bipolar transistors

• Published in: Materials science and technology 1995-10, Vol.11 (10), p.1083-1088
• Main Authors: Sandhu, K. S., Staton-Bevan, A. E., Crouch, M. A.
• Format: Article
• Language: English
• ISSN: 0267-0836; 1743-2847
• DOI: 10.1179/mst.1995.11.10.1083

The microstructure and electrical properties of as deposited and annealed Au (400 nm)/Pd (75 nm)/Ti (10 nm) contact structures to p type GaAs, C doped with a concentration of 5 × 10 18 and 5 × 10 19 cm −3 , have been investigated using transmission electron microscopy, and current-voltage measurements as afunction of temperature in the range 198-348 K. The specific contact resistivities have also been measured using the transmission line method. It was found that increasing the epilayer doping level by an order of magnitude, from 5 × 10 18 to 5 × 10 19 cm −3 , caused the dominant current transport mechanism to change from thermionic field emission to field emission. For the lower level doped epilayers generationrecombination within the depletion region was found to be the dominant current transport mechanism for temperatures below 289 K. The contacts to the more highly doped epilayers (C doped, 5 × 10 19 cm −3 ) had specific contact resistivities of 0·08 ± 0·03 Ωmm and 0·05 ± 0·06 Ωmm, respectively. These values, together with a minimal metal penetration in the semiconductor of