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

The stability of the crystalline phase of binary phase-change GexSb1-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 TGep to the rate of change dTcryst/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% < or approx. x < 50% window, that may achieve the desired cycling/archival properties of a phase-change cell.