Non-conventional routes to SiGe:P/Si(100) materials and devices based on -SiH₃ and -GeH₃ derivatives of phosphorus: Synthesis, electrical performance and optical behavior

Ge-Si based n-type films are synthesized using specially designed hydrides P(SiH₃)₃, Ge₃H₈ and Ge₄H₁₀ for potential applications in next-generation CMOS technologies. The films are grown on Ge buffered Si(100) at 340°C using two complementary methods. The first employs a gas-source molecular epitaxy approach using Ge₄H₁₀ to produce materials with P doping densities varying from 4×10¹⁸ to a 3.5×10¹⁹ cm^-3 threshold. These materials are co-doped with Si concentrations ranging from 3×10¹⁹ cm^-3 to 3.5%, roughly in proportion with the amount of P(SiH₃)₃ used in the reactions. The second approach applies an alternative ultra-high vacuum chemical vapor deposition (UHV-CVD) technique and Ge₃H₈ in place of Ge₄H₁₀ to achieve ultra-high carrier concentrations up to ∼6×10¹⁹ cm^-3. The Si content in this case is minimal - in the 2-6×10¹⁹ cm^-3 range - indicating that the growth mechanism allows only 'impurity' levels of Si to be incorporated. The active carrier densities in both cases closely reflect the absolute P content, indicating that the P atoms are mostly substitutional. The electron mobilities are significantly higher compared to state-of-the-art prototypes, probably due to superior microstructure and dearth of inactive donors in the lattice. P-I-N diodes fabricated using the P(SiH₃)₃ compound show I-V characteristics comparable to state-of-the-art results for Ge-on-Si devices and are virtually undistinguishable from similar diodes doped with the P(GeH₃)₃ precursor. These results confirm P(SiH₃)₃ as a viable CVD doping source that is practical from a process standpoint and therefore attractive for industrial scale-up.