Theoretical and Experimental Investigations of the Optical Properties of Ge2Sb2Te5 for Multi-State Optical Data Storage

Abstract

Ge2Sb2Te5 (GST) is widely used as an excellent data recording material based on its fast and reversible amorphous-to-crystalline phase transformation that is accompanied by changes in the optical re ectivity and the electrical conductivity. It was demonstrated that GST can be transformed reversibly between the amorphous and the cubic phases, and, under certain conditions, it can be transformed between the cubic and the hexagonal phases as well. Thus, if we can take advantage of the di erences in the optical and the electrical properties among the amorphous, the cubic, and the hexagonal states, we could use GST as a multi-state storage material, and its storage density would be improved remarkably. In this study, we investigate the electronic and the optical properties of crystalline GST by using both ab-initio and experimental analyses. The results show that the cubic GST is semi-conductive while the hexagonal GST may exhibit much higher conductivity. The re ectivity contrast of the two crystalline states is above 8 % in the range from 400 nm to 700 nm, indicating a potential for applications of GST in multi-state optical data storage.