Ruthenium and ruthenium-based contacts to GaAs

Abstract

This paper deals with the outstanding electrical and structural properties of Ru-based Schottky and ohmic contacts fabricated by electron beam evaporation on n- and p + -type GaAs, respectively. The effective and flatband barrier heights were evaluated by standard current-voltage ( I–V)( T) and capacitance-voltage ( C–V)( T) measurements, over the temperature ( T) range 100 to 350 K. The modified Richardson constant, A ∗∗, varied between 2.2 and 4.9 A cm −2 K -2, depending upon the annealing temperature. AES depth profiles indicated that Ru forms structurally very stable contacts to GaAs, with no evidence from XPS measurements of any compound formation between Ru and GaAs even after annealing up to 500°C. A sharp increase was observed in the formation of Ga 2O 3 at the interface between the Ru layer and the GaAs after vacuum annealings at temperatures of 450°C and above. Only limited diffusion of arsenic through the Ru layer was observed after annealing at 400°C, but increased rapidly above 450°C. A Au/Ru/p +-GaAs ohmic contact system showed comparable specific contact resistance (5.5×10 −6 Ω·cm 2) to those systems commonly used, but with superior surface morphology.