  Optical properties of dislocations free state-of-the-art Germanium(Ge) and
Germanium-oninsulator(GeOI) wafers have been characterized using Fourier
transformed infrared spectroscopy at oblique incidence, attenuated total
reflectance, laser Raman scattering, linear and nonlinear optical transmission.
In n-type Ge, in addition to vibrational modes observed in intrinsic(i) Ge, a
band at 535cm-1 which is likely due to carbon and a strong peak at 668 cm-1
were observed at non-normal incidence. Despite the strong heavy hole to light
hole absorption band at low energies, the 668 cm-1 peak was also observed in
p-Ge. The appearance of new bands and the enhancement in band strength are in
general observed in both type of wafers at oblique incidence. GeOI exhibits a
strong disorder induced LO-TO coupling mode which can only be observed at
non-normal incidence. Optical absorption at the near bang 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. Different nonlinear optical
absorption behavior was observed in n-Ge, p-Ge and GeOI wafers. The p-Ge
becomes transparent to CO2 laser line at 10.6 micrometer, while transmitted
power decreases in n-Ge with increasing UV-VIS pump power.
