PD-BASED OHMIC CONTACTS TO N-GASB

Electron beam evaporated Ge/Pd, Ge/Pd/Sb, Pd/Sb and Pd contacts to n-G aSb are produced. The I-V characteristics of as-deposited and annealed at 250 to 450 degrees C diode structures are measured and R-c is spec ified. The ohmic behavior of Ge-containing contacts is reached after a nnealing at 300 to 325 degrees C. The transition is either due to n-Ge /n-GaSb heterojunction formation or to Ge incorporation on V-Ga depend ing on the Ge/Pd layer thickness ratio. The Pd and Pd/Sb contacts beco me ohmic at 350 and 300 degrees C, respectively. The lowest R-c (10(-3 ) to 10(-4) Ohm cm(2)) and the best thermal stability up to 450 degree s C is exhibited by the Pd/Sb contact. This results allowed us to inte rpret the degradation of the Pd-based contacts at T-ann greater than o r equal to 400 degrees C in terms of V-Sb formation and GaSb surface p artial compensation. An X-ray microprobe analysis of the Ge/Pd contact composition upon annealing is performed.