Nature of gap states in GeSbTe phase change memory materials

Abstract

We have calculated the states associated with valence alternation pair defects in a Te-rich amorphous GeTe random network. Two-fold Te sites and four-fold Ge sites are found to introduce states that are resonant with the valence and conduction bands, respectively. The system has a band gap, but these defect states are in the same energy range as those found by modulated photocurrent experiments. The absence of electron spin resonance signals is still not explained.