ELECTRICAL EVALUATION OF AL-P(-GEXSI1-X OHMIC CONTACTS())

The electrical properties of Al-p(+)-GexSi1-x contacts were studied us ing transmission line measurements. For this study the GeSi alloy laye rs were selectively formed with 30 or 90 keV Ge implantation into Si, a technique which offers a simple, self-aligned process for the fabric ation of such layers. Measurements of the current-voltage characterist ics showed that the metal-alloy contacts were ohmic over the voltage r ange examined. The specific contact resistivity was found to be a func tion of Ge concentration, decreasing with increasing Ge concentration for concentrations below a critical value and increasing with increasi ng Ge concentration above this value. The initial decrease in specific contact resistivity is attributed to the effect of Ge on the contact barrier height and width, an effect which is caused by the reduction i n the band gap of the alloy. The subsequent increase in specific conta ct resistivity at higher Ge concentrations is believed to be due to th e presence of a high concentration of dislocations in the alloy layer. The thermal stability of contacts is also reported. (C) 1996 American Institute of Physics.