Reduced pressure-chemical vapor deposition of intrinsic and doped Ge layers on Si(0Â 0Â 1) for microelectronics and optoelectronics purposes

We have investigated the structural properties of Ge thick films grown directly onto Si(0 0 1) substrates using a production-compatible reduced pressure-chemical vapor deposition system. The thick Ge layers grown using germane and a low-temperature/high-temperature approach are in a definite tensile-strain configuration. The threading dislocation density is as low as 6×106 cm−2 for 2.5 μm-thick layers that have subsequently been submitted to a 8 times {750 °C, 10 min/900 °C, 10 min} cyclic anneal under H2. The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch in-between Ge and Si. The root mean square roughness is indeed of the order of 1 nm only for 2.5 μm thick Ge layers. Some out-diffusion of Si towards the surface of the Ge layer has also been evidenced, with diffusion coefficients slightly higher than those of pre-implanted Si inside bulk Ge. Finally, we have studied the in situ n- and p-type doping of Ge. A B ions concentration as high as 1×1020 cm−3 has been achieved at 400 °C inside Ge using diborane as a gaseous precursor. Meanwhile, the P ions concentration at 850 °C fluctuates in-between 1×1017 and 4×1017 cm−3 more or less independently of the phosphine flow. This is most probably due to some significant surface segregation of P.