Optical characterization of dislocation free Ge and GeOI wafers

TL;DR

This study comprehensively characterizes the optical properties of dislocation-free Ge and GeOI wafers using various spectroscopic techniques, revealing new vibrational modes, disorder effects, and nonlinear optical behaviors.

Contribution

It provides novel insights into the optical characteristics of high-quality Ge and GeOI wafers, including the observation of new vibrational bands and nonlinear absorption phenomena.

Findings

Observation of new vibrational bands at oblique incidence.

Detection of disorder-induced LO-TO coupling in GeOI.

Different nonlinear optical absorption behaviors in n-Ge, p-Ge, and GeOI.

Abstract

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.