New GeSi doping strategies based on P(SiH$_{3})_{3}$ for next-generation CMOS technologies*

GeSi $n$-type films are synthesized using the specially designed hydrides P(SiH$_{3})_{3}$, Ge$_{3}$H$_{8}$ and Ge$_{4}$H$_{10}$ for applications in next-generation CMOS technologies. The films are grown on Ge-buffered Si(100) at 340 $^{\circ}$C using two methods. The first employs a gas-source molecular epitaxy approach and Ge$_{4}$H$_{10}$ to yield films with P doping densities up to 3.5 x 10$^{19}$/cm$^{3}$. The amount of Si incorporated equals or exceeds the 3:1 ratio in the P(SiH$_{3}$)$_{3}$ compound. The second approach applies an ultra-high vacuum chemical vapor deposition technique and Ge$_{3}$H$_{8}$ in place of Ge$_{4}$H$_{10}$ to achieve higher carrier concentrations up to 6 x 10$^{19}$/cm$^{3}$. The Si:P ratio in this case is well below the 3:1 value expected from the precursor. The electron mobilities for both types of samples are significantly higher than state-of-the-art prototypes, probably due to superior microstructure and dearth of inactive donors. The relative stability of Si-P and Ge-P bonds in a Ge matrix is studied with \textit{ab initio} methods. $P-I-N $diodes fabricated using P(SiH$_{3}$)$_{3}$ show excellent $I$-$V$ characteristics that are virtually undistinguishable from similar diodes doped with the P(GeH$_{3}$)$_{3}$ precursor. These results confirm P(SiH$_{3}$)$_{3}$ as a viable doping source that is practical from a process standpoint and therefore attractive for industrial scale-up.