Temperature dependent optical constants of amorphous Ge2Sb2Te5 thin films

This study focuses on the temperature dependent optical band gap changes in the amorphous Ge2Sb2Te5 (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 (B1/2) are studied for different temperatures and discussed. The observed changes in optical band gap (Eg) are fitting to Fanʹs one phonon approximation. Phonon energy (ћω) corresponding to a frequency of 3.59 THz is derived from Fanʹs approximation, which is close to the reported value of 3.66 THz.