Local atomic order and optical properties in amorphous and laser-crystallized GeTe

In this work we study the role of short-range order changes upon amorphization on the optical properties of GeTe \textendash a prototype phase change material employed for optical data storage. It is found that the profound change in the absorption is due to changes in the matrix elements of the optical transitions. The importance of the local distortions in the crystalline phase for the optical absorption are revealed as well. Modifying the degree of the distortions has a significant impact on the optical properties of the crystalline state and should therefore become a promising instrument to improve material properties for storage applications. Furthermore we study the effect of electron\textendashelectron and electron\textendashhole interactions on the optical properties. This is achieved by evaluating many-body effects in the crystalline phase through a GW correction of eigenvalues and the solution of the Bethe\textendashSalpeter equation.