Temperature dependent optical constants of amorphous Ge 2Sb 2Te 5 thin films

Abstract

This study focuses on the temperature dependent optical band gap changes in the amorphous Ge 2Sb 2Te 5 (GST) films. The behavior of the amorphous GST thin films at low temperatures has been studied. The band gap increment of around 0.2 eV is observed at low temperature (4.2 K) compared to room temperature (300 K). The band gap changes associated with the temperature are completely reversible. The other optical parameters like Urbach energy and Tauc parameter (B 1/2) are studied for different temperatures and discussed. The observed changes in optical band gap (E g) are fitting to Fan's one phonon approximation. Phonon energy (ћω) corresponding to a frequency of 3.59 THz is derived from Fan's approximation, which is close to the reported value of 3.66 THz.