Simulations of Infrared Reflectivity and Transmission Phonon Spectra for Undoped and Doped GeC/Si (001)

Exploring the phonon characteristics of novel group-IV binary XC (X = Si, Ge, Sn) carbides and their polymorphs has recently gained considerable scientific/technological interest as promising alternatives to Si for high-temperature, high-power, optoelectronic, gas-sensing, and photovoltaic applications. Historically, the effects of phonons on materials were considered to be a hindrance. However, modern research has confirmed that the coupling of phonons in solids initiates excitations, causing several impacts on their thermal, dielectric, and electronic properties. These studies have motivated many scientists to design low-dimensional heterostructures and investigate their lattice dynamical properties. Proper simulation/characterization of phonons in XC materials and ultrathin epilayers has been challenging. Achieving the high crystalline quality of heteroepitaxial multilayer films on different substrates with flat surfaces, intra-wafer, and wafer-to-wafer uniformity is not only inspiring but crucial for their use as functional components to boost the performance of different nano-optoelectronic devices. Despite many efforts in growing strained zinc-blende (zb) GeC/Si (001) epifilms, no IR measurements exist to monitor the effects of surface roughness on spectral interference fringes. Here, we emphasize the importance of infrared reflectivity Rω and transmission Tω spectroscopy at near normal θ<i>_i</i> = 0 and oblique θ<i>_i</i> ≠ 0 incidence (Berreman effect) for comprehending the phonon characteristics of both undoped and doped GeC/Si (001) epilayers. Methodical simulations of Rω and Tω revealing atypical fringe contrasts in ultrathin GeC/Si are linked to the conducting transition layer and/or surface roughness. This research provided strong perspectives that the Berreman effect can complement Raman scattering spectroscopy for allowing the identification of longitudinal optical ωLO phonons, transverse optical ωTO phonons, and LO-phonon-plasmon coupled ωLPP+ modes, respectively.