Schottky and ohmic contacts to doped Si1-x-yGexCy layers

We report on titanium contacts to n-type and p-type Si1-x-yGexCy strained h eteroepitaxial layers on (100)Si and material and electrical characterizati on of n-type and p-type platinum-silicide-germanide contacts to Si1-x-yGexC y strained heteroepitaxial layers on (100)Si. Ti contacts to n-type Si1-x-y GexCy show rectifying behavior at low doping levels but become ohmic as lay ers reach 10(18) cm(-3). Ti contacts to p-type Si1-x-yGexCy/Si are ohmic at doping levels as low as 10(15) cm(-3), Contact resistances for Ti/Si1-x-yG exCy contacts had values ranging from 10(-1) to 10(-2) Omega cm(2). X-ray diffraction (XRD) studies of rapid thermal anneal (RTA) silicidation of Pr on SiGeC indicate the reaction proceeds from elemental Pt to Pt-2(SiG eC) and ends in the Pt(SiGeC) phase, analogous to Pt/Si silicides. However, the Pt-silicide-germanide reaction with SiGeC requires higher temperatures than the counterpart Pt reaction with Si. Pt(SiGeC) contacts to n-type SiG eC layers show rectifying behavior with nonideality factors (n) of 1.02 to 1.05 and constant barrier heights of 0.67 eV independent of composition, in dicating that Fermi level pinning relative to the SiGeC conduction band is occurring. For contact doping levels of 10(18) cm(-3) and above, Pt(SiGeC) contacts to n-type SiGeC layers are ohmic with constant contact resistance values of 10(-2) Omega cm(2) Pt(SiGeC) contacts to p-type Si1-x-yGexCy/Si w ere ohmic over the entire doping range studied, with resistances from the 1 Omega cm(2) range at intrinsic alloy doping levels, to the 10(-2) Omega cm (2) range for doping levels of 10(18) cm(-3). Using Pt(SiGeC) ohmic contacts to p-type SiGeC, current-voltage measurement s of Si1-x-yGexCy to (100)Si heterojunctions are also presented. Heterojunc tion barrier heights track the variation of the SiGeC energy bandgap to a f actor of 0.84 x. The Si1-x-yGexCy/Si heterojunction valence band discontinu ity, Delta E-v, decreases 15 meV per %C incorporated into the strained allo y layer for 0 < y < 0.01 and increases Delta E-v by 2.8 meV per %Ge for 0 < x < 0.11. (C) 1999 Elsevier Science Ltd. All rights reserved.