DOPING OF GAAS USING SF6 PLASMA TREATMENT

We propose a new method of making heavily doped n-type GaAs to a very shallow depth using sulfur hexafluoride (SF6) plasma treatment of the GaAs surface. Semi-insulating GaAs substrate implanted with Si was exp osed to a sulfur containing SF6 plasma and capped with silicon nitride anneal cap. During a subsequent anneal step at an elevated temperatur e to electrically activate the implanted Si, the sulfur diffused into GaAs to a shallow depth of approximately 600 angstrom resulting in fur ther enhancement of net carrier concentration. With this technique the carrier concentration near the surface region was almost doubled comp ared to samples with Si implantation only. The enhanced carrier concen tration improved the wafer-scale variation of ohmic contact resistance using AuGeNi contact metals from 0.089 +/- 0.073 to 0.049 +/- 0.017 O MEGA mm. The surface chemistry of SF6 plasma treated GaAs surface was characterized by x-ray photoelectron spectroscopy and Auger electron s pectroscopy, and the results were compared with the carrier-concentrat ion profiles and ohmic contact resistance.