Amorphous-to-crystalline phase transition in Ge-rich Ge-Te-Zn films with high thermal stability

• Zn16.1Ge57Te26.9 thin film has better thermal stability.
• Zn16.1Ge57Te26.9 thin film has higher crystalline resistance.
• Zn16.1Ge57Te26.9 has a high amorphous/crystalline resistance ratio of about 105.
• No phase separation is observed in Zn16.1Ge57Te26.9 film.

Ge-rich Ge-Te-Zn thin films were investigated for phase change memory application. The crystallization behavior is improved by adding Zn into the Ge2Te material. The crystallization temperature of the Zn16.1Ge57Te26.9 film is 297 °C and the crystalline activation energy is about 4.02 eV. The 10-years’ failure temperature for Zn16.1Ge57Te26.9 film is about 202.4 °C, implying high thermal stability. In addition, the sheet resistances of amorphous Zn16.1Ge57Te26.9 film decreases with increasing temperature until an abrupt drop at the crystallization temperature with about 5 orders-of-magnitude resistance change. The precipitated crystals are confirmed to be single Ge2Te phases and the obtained optical band gap decreases from 0.75 eV to 0.29 eV as it transforms from amorphous phase to crystalline phase. The Zn-doped Ge-rich Zn-Ge-Te films with a moderate Zn content (16.1 at.%) is preferable for phase-change memory applications.