Optical characterization of dislocation free Ge and GeOI wafers

Optical properties of dislocations free state-of-the-art Germanium(Ge) and Germanium-on-insulator(GeOI) wafers have been characterized using Fourier transformed infrared spectroscopy at oblique incidence, attenuated total reflectance, laser Raman scattering and optical transmission at room temperature. In n-type Ge, in addition to vibrational modes observed in intrinsic(i) Ge, a band at 535 cm−1, 668 cm−1 and a strong peak at 1590 cm−1 were observed. At oblique incidence, the bands at high energies loose their intensity and those at 500–600 cm−1 become stronger and new bands appear at 840 and 945 cm−1. Thermal annealing reveals the precipitation of GeO as evidenced from the band structure at 845 cm−1 and an absorption dip at 808 cm−1 in p-type Ge. The appearance of new bands and the change in band strengths are in general observed in both type of wafers at oblique incidence. GeOI exhibits a strong disorder induced longitudinal optic (LO)–TO coupling mode which can only be observed at non-normal incidence. Optical absorption at the near band edge reveals the presence of doping related disorder and band shrinkage, which is supported also by Ge–Ge one-phonon line broadening at 301 cm−1.