Infrared optical constants of orthorhombic IV-VI lamellar semiconductors refined by a combined study using optical and electronic spectroscopies

Cleaved surfaces of the IV-VI lamellar semiconducting compounds GeS, GeSe, SnS, and SnSe have been studied by high-resolution electron-energy-loss spectroscopy (HREELS). The infrared optical constants of the materials were obtained by using the dielectric theory taking into account the resonance frequencies published from infrared reflectivity (IRS) data. The limitations of the HREELS and IRS measurements in the case of these materials are discussed in detail. It is shown that, by combining the information from both spectroscopies, it is possible to determine better some of the oscillator strengths of these materials. In addition to a linear relationship between the phonon frequencies of GeSe and GeS, and SnSe and SnS, a similar relationship was also found between their oscillator strengths, which may provide an improved understanding of the lattice properties of these lamellar compounds.