Correlation between optical absorption redshift and carrier density in phase change materials

Abstract

Here, we report an optical absorption redshift map for GeTe-Sb 2 Te 3 pseudo-binary alloys. We found that, with phase change from amorphous to crystalline, the observed redshift increases with Ge concentration along pseudo-line of compositions, which directly reflects the enhanced electron delocalization/resonant bonding and increased carrier concentrations in the respective crystal compounds. The measured valence band maximum shift towards the Fermi energy from amorphous to crystalline phase supports the observed similar trend in redshift and carrier density. We show that the correlation between optical redshift and carrier density, attributed to the resonant bonding, can be rationalized by calculating the valence electron concentration, the ionicity, and hybridization. V

Topological Phase Buried in a Chalcogenide Superlattice Monitored by Helicity-Dependent Kerr Measurement

“…Optical measurements were carried out using a reflection geometry pump− probe setup (see Figure 1), which consisted of a Ti:sapphire laser system that generated a train of <20 fs pulses at a wavelength of 830 nm (≈1.5 eV) at an 80 MHz repetition rate. The optical penetration depth at 830 nm was calculated to be ∼20 nm, 28 which is greater than the sample thickness up to the moderate GeTe layer thickness sample (4.3 nm). Thus, the effects of the optical penetration depth do not play an important role due to the presence of homogeneous optical excitation over the entire sample thickness, except for the thickest sample (GeTe layer thickness of 8.6 nm).…”

Investigation of amorphous-crystalline transformation induced optical and electronic properties change in annealed As50Se50 thin films

“…5 T and R spectra of the studied films decreased for the 423 K annealed film. As the film structure was converted into a crystalline one, the α value increased than that of the amorphous one (Ho et al 2013).…”

Disorder and compositional dependences in Urbach-Martienssen tails in amorphous (GeTe)x(Sb2Te3)1−x alloys

“…1). The obtained results revealed the compositional dependence in the E g , as studied GST are mixtures of parent binary compounds, they inherit their properties in the corresponding proportion 27 . The values of the dielectric constant and the optical bandgap of Ge 1 Sb 2 Te 4 , Ge 2 Sb 2 Te 5 , and GeTe are in the quantitative consistency with data previously reported in 3 , where the samples have been prepared in the same manner using magnetron sputtering method.…”