Influence of the local structure in phase-change materials on their dielectric permittivity

Abstract

Ge-Sb-Te alloys, which belong to the phase-change materials, are promising materials for data storage and display and data visualization applications due to their unique properties. This includes a remarkable difference of their electrical and optical properties in the amorphous and crystalline state. Pronounced change of optical properties for Ge-Sb-Te alloys is linked to the different bonding types and different atomic arrangements in amorphous and crystalline states. The dielectric function of phase-change materials has been investigated in the far infrared (FIR) range. Phonons have been detected by FTIR spectroscopy. Difference of the dispersion of the dielectric permittivity of amorphous and crystalline samples is caused by different structures in different states which contribute to the dielectric permittivity.

Evidence for resonant bonding in phase-change materials studied by IR spectroscopy

“…The difference in the profile of ε 2 is shown in Fig. 4 can be attributed to different local atomic arrangement in the amorphous and crystalline states of PCM [16]; larger coordination number, longer bond length and larger coefficient of thermal expansion explain softening the phonon modes in the crystalline states of PCM [17]. These two phenomena provide evidence that the bonding type in the crystalline state of PCM is not the same as that inherent to the amorphous state, i.e., covalent bonding.…”