Abstract
This study was divided into two sections. Section 1 explored the equilibrium phase relations of the (Ge4SbTe5)1-xBix (x = 0~0.5) pseudo-binary alloy system. And section 2 studied the thin film properties of compositions Ge4SbTe5 and Ge4Sb0.5Bi0.5Te5. Four constituents were found in the as-cast (Ge4SbTe5)1-xBix system, that were GeTe, BiTe, Ge, and Bi. The GeTe constituent possesses rhombohedral structure except the Ge4SbTe5 composition, which was identified as FCC structure; and the BiTe constituent belongs to hexagonal structure except at x= 0.5. After 400℃ annealing for 2 weeks, the solubility of Sb and Bi in GeTe constituent increases as a result of atomic diffusion between GeTe and BiTe constituents, besides Ge precipitation appears at the same time. The annealed GeTe constituent at x= 0.1 shows stable FCC structure; and the BiTe constituent changes from hexagonal structure to longer periodicity rhombohedral structure as increasing Bi content. Thin films of compositions Ge4SbTe5 and Ge4Sb0.5Bi0.5Te5 were prepared by RF magnetron sputtering. The Ge contents of thin films were much lower than expected, this was caused by the appearance of low sputtering yield Ge phase in the target. The structure of crystallized films is both FCC, with lattice expansion found in Bi containing film. The DSC results showed that Bi addition can decreases the crystallization temperature and activation energy, which were measured as 202℃and 2.7 eV respectively in the case of 5% Bi substitution. Both Ge4SbTe5 and Ge4Sb0.5Bi0.5Te5 films have high optical contrast above 30%, this phenomena was related to the increase in k value and decrease in n value in the crystalline state.