Sub-gap states in Ge2Sb2Te5 phase change films

Abstract Sub-gap absorption spectra of as-deposited and thermal annealed Ge 2 Sb 2 Te 5 films have been investigated using extended photothermal deflection spectroscopy from 0.31 to 2.5 eV (500 to 4000 nm). We found sub-gap absorption peak at 0.41 eV in the spectra of annealed samples. The intensity of the absorption peak increased with annealing temperature above 140 °C. This result implies that intrinsic structural defect in fcc-Ge 2 Sb 2 Te 5 is related to forming sub-gap states. Vacancies in fcc-Ge 2 Sb 2 Te 5 form gap states above the valence band edge, leading to p -type conduction.