Influence of Partial Substitution of Te by Se and Ge by Sn on the Properties of the Blu-ray Phase-Change Material Ge₈Sb₂Te₁₁

The opto-electronic properties of the Blu-ray phase-change material Ge 8 Sb 2 Te 11 were investigated and compared to partially substituted compounds. Investigations were performed on Ge 8 Sb 2 Te 6 Se 5 ( I ) and SnGe 7 Sb 2 Te 7 Se 4 ( II ). To monitor the influence of substitution on both cation and anion sites onto the properties, in Ge 8 Sb 2 Te 6 Se 5, only Te was substituted by Se, while in SnGe 7 Sb 2 Te 7 Se 4, Ge also was partially replaced by Sn, yielding an equivalent degree of substitution. The crystallization of the amorphous compound to a rhombohedral phase was observed. The first transition temperature ( T c1 ) is 210 °C for I and 185 °C for II, while the second transition temperature ( T c2 ) cannot be clearly determined, because of the coexistence of both phases. Thin-film properties were examined and an increase of density and roughness was observed for both materials upon crystallization. In situ electrical resistance measurements show a huge electrical contrast between the amorphous samples and the crystalline samples, which amounts to 4 orders of magnitude for II and 5 orders of magnitude for I . Optical properties were characterized with variable incident-angle spectroscopic ellipsometry (VASE) and Fourier Transform infrared (FTIR) spectroscopy. Substitution leads to an enormous increase of the reflectivity contrast for blue light: The reflectivity contrast between the different phases increases from 20% to 50% for I and from 20% to 74% for II .