Schottky and ohmic contacts to doped Si1ÿxÿyGexCy layers
نویسندگان
چکیده
We report on titanium contacts to n-type and p-type Si1ÿxÿyGexCy strained heteroepitaxial layers on (100)Si and material and electrical characterization of n-type and p-type platinum±silicide±germanide contacts to Si1ÿxÿyGexCy strained heteroepitaxial layers on (100)Si. Ti contacts to n-type Si1ÿxÿyGexCy show rectifying behavior at low doping levels but become ohmic as layers reach 10 cmÿ3. Ti contacts to p-type Si1ÿxÿyGexCy/Si are ohmic at doping levels as low as 10 cmÿ3. Contact resistances for Ti/Si1ÿxÿyGexCy contacts had values ranging from 10 ÿ1 to 10ÿ2 O cm. X-ray diraction (XRD) studies of rapid thermal anneal (RTA) silicidation of Pt on SiGeC indicate the reaction proceeds from elemental Pt to Pt2(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 cmÿ3 and above, Pt(SiGeC) contacts to n-type SiGeC layers are ohmic with constant contact resistance values of 10ÿ2 O cm. Pt(SiGeC) contacts to p-type Si1ÿxÿyGexCy/Si were ohmic over the entire doping range studied, with resistances from the 1 O cm 2 range at intrinsic alloy doping levels, to the 10ÿ2 O cm range for doping levels of 10 cmÿ3. Using Pt(SiGeC) ohmic contacts to p-type SiGeC, current±voltage measurements of Si1ÿxÿyGexCy 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 Si1ÿxÿyGexCy/Si heterojunction valence band discontinuity, DEv, decreases 15 meV per %C incorporated into the strained alloy layer for 0 < y< 0.01 and increases DEv by 2.8 meV per %Ge for 0 < x < 0.11. # 1999 Elsevier Science Ltd. All rights reserved.
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