Improvement of current drive of Ge-nMISFETs by epitaxially grown n+-Ge:P source and drain

Abstract

n⁺-Ge layers with a dopant concentration of 1 × 10²⁰ cm^-3 and its dopant activation rate as high as 0.7 were obtained by optimizing the growth conditions in LP-CVD. Ti/n⁺-Ge contacts utilizing Ge:P layers with a carrier concentration of 7 × 10¹⁹ cm^-3 exhibit ohmic property in contrast to the P ion-implanted Ge samples with almost the same P concentration and carrier concentration of 2 × 10¹⁹ cm^-3. Thus, a ρ_c value as low as 1.2 × 10^-6 Ωcm² was obtained for the Ti / Ge:P contact. A low R_sh of 33 (Ω/sqr.) was shown for the 65-nm-thick P-doped Ge layer due to the high carrier concentration. The value of R_sh for the epi-layer agrees with the theoretically predicted value, also resulting in reduction of parasitic resistances of the Ge-nMISFETs. The largest I_d of Ge-nMISFET was obtained by utilizing the Ge:P to elevated S/D region of GeOI-nMISFETs. We can say that these results pave the way to the feasibility of Ge-CMOS.