Reduced pressure-chemical vapor deposition of intrinsic and doped Ge layers on Si(0 0 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 6×10 6 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 H 2. 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 1×10 20 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 1×10 17 and 4×10 17 cm −3 more or less independently of the phosphine flow. This is most probably due to some significant surface segregation of P.