Doping and electrical characteristics of in situ heavily B-doped Si_1-xGe_x films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in situ heavily B-doped Si_1-xGe_x (0.15 < x < 0.80) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH₄-GeH₄-B₂H₆-H₂ gas mixture by using an ultraclean hot-wall low pressure chemical vapor deposition (LPCVD) system. With increasing B₂H₆ partial pressure, the deposition rate decreased only at the higher GeH₄ partial pressure, and the B concentration (C_B) in the film increased proportionally up to 10²² cm^-3. The Ge fraction scarcely changed with the B₂H₆ addition. The carrier concentration was nearly equal to C_B up to about 2 × 10²⁰ cm^-3, and it tended to be saturated at around 5 × 10²⁰ cm^-3 at C_B <∼ 10²² cm^-3. In other words, electrically inactive B increased with increasing C_B above 2 × 10²⁰ cm^-3. The resistivity decreased with increasing carrier concentration at C_B <∼ 10²² cm^-3 and was influenced by alloy scattering. Discrepancy of the lattice constants from Vegard's law was observed at higher C_B in the order of 10²⁰ cm^-3 and above, which corresponded with the saturation of the carrier concentration.