GAAS SURFACE PLASMA TREATMENTS FOR SCHOTTKY CONTACTS

The properties of different rectifying metallizations (Al, Ti/Pt, WNx on GaAs have been investigated for various surface preparation procedures. In particular, in situ hydrogen plasma treatments were used to remove residual surface contamination (mainly O and C) and a nitrogen plasma to grow a thin mixed nitride layer. Al and Ti/Pt Schottky diodes with an ideality factor very close to 1, but with reduced barrier height, were found after the H-2 plasma as a consequence of H diffusion into GaAs. The Schottky barrier height was further reduced if a H-2 + N2 plasma was performed. The N content in the sputtering environment during the WNx deposition affects the diode properties of plasma-treated WNx contacts. By increasing the N2 partial pressure, the diode barrier height is reduced, probably due to nitridization of the GaAs surface. Such differences disappear after annealing the diodes in arsine overpressure at 800-degrees-C. WNx contacts deposited under different conditions on H-2 plasma treated substrates also show a similar Schottky barrier height after such annealing.