Irreversible altering of crystalline phase of phase-change Ge-Sb thin films

The stability of the crystalline phase of binary phase-change Gex Sb1-x films is investigated over a wide range of Ge content. From Raman spectroscopy we find the Ge-Sb crystalline structure irreversibly altered after exposure to a laser beam. We show that with increasing beam intensity/temperature Ge agglomerates and precipitates out in the amount growing with x. A simple empirical relation links Ge precipitation temperature T Ge p to the rate of change d Tcryst /dx of crystallization, with the precipitation easiest on the mid-range x plateau, where Tcryst is nearly constant. Our findings point to a preferable 15%≤x≤50% window, that may achieve the desired cycling/archival properties of a phase-change cell. © 2010 American Institute of Physics.