Schottky and ohmic contacts to doped Si 1− x− yGe xC y layers

Abstract

We report on titanium contacts to n-type and p-type Si 1− x− y Ge x C y strained heteroepitaxial layers on (100)Si and material and electrical characterization of n-type and p-type platinum–silicide–germanide contacts to Si 1− x− y Ge x C y strained heteroepitaxial layers on (100)Si. Ti contacts to n-type Si 1− x− y Ge x C y show rectifying behavior at low doping levels but become ohmic as layers reach 10 18 cm −3. Ti contacts to p-type Si 1− x− y Ge x C y /Si are ohmic at doping levels as low as 10 15 cm −3. Contact resistances for Ti/Si 1− x− y Ge x C y contacts had values ranging from 10 −1 to 10 −2 Ω cm 2. X-ray diffraction (XRD) studies of rapid thermal anneal (RTA) silicidation of Pt on SiGeC indicate the reaction proceeds from elemental Pt to Pt 2(SiGeC) 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 SiGeC 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, indicating 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 Ω cm 2. Pt(SiGeC) contacts to p-type Si 1− x− y Ge x C y /Si were ohmic over the entire doping range studied, with resistances from the 1 Ω cm 2 range at intrinsic alloy doping levels, to the 10 −2 Ω cm 2 range for doping levels of 10 18 cm −3. Using Pt(SiGeC) ohmic contacts to p-type SiGeC, current–voltage measurements of Si 1− x− y Ge x C y to (100)Si heterojunctions are also presented. Heterojunction barrier heights track the variation of the SiGeC energy bandgap to a factor of 0.84×. The Si 1− x− y Ge x C y /Si heterojunction valence band discontinuity, Δ E v, decreases 15 meV per %C incorporated into the strained alloy layer for 0< y<0.01 and increases Δ E v by 2.8 meV per %Ge for 0< x<0.11.