In situ doped epitaxial growth of highly dopant-activated n+-Ge layers for reduction of parasitic resistance in Ge-nMISFETs

We selectively grew n+-Ge layers with a carrier concentration as high as 7 × 1019 cm−3 for use as the source and drain regions of Ge-nMISFETs by low-pressure CVD. A high activation rate of 73% for the P-dopant was achieved only within a narrow window of total growth pressure. Ti contacts on the P-doped n+-Ge epilayers exhibited ohmic properties in contrast to those on P-ion-implanted Ge layers of almost the same dopant concentration. Low sheet resistance of 33 Ω/sq and low specific contact resistivity of 1.2 × 10−6 Ω·cm2 were obtained for the 65-nm-thick epi-Ge layers as a result of the high activation rate.