ROLE OF NATIVE OXIDE IN THE ACTIVATION OF IMPLANTED SI IN GAAS

We have investigated the effect of oxygen plasma treatment on GaAs surface prior to plasma enhanced chemical vapor deposition of silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency by approximately 35% over (1:10) NH4OH:H2O treatment. In addition, the oxygen plasma treated samples had uniform sheet resistance across the wafer with minimum wafer-to-wafer variations. X-ray photoelectron spectroscopy analysis of oxygen plasma treated GaAs surface indicated the formation of approximately 25-angstrom-thick oxide layer consisting of Ga2O3, As2O3, As2O5, and elemental As. During the activation anneal, the arsenic-containing oxides react with the GaAs substrate to form Ga2O3 and elemental As which increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency. The higher and uniform activation efficiency for high Si implants improved the wafer scale variation of ohmic contact resistance to n+-GaAs.