Change in electrical resistance and thermal stability of nitrogen incorporated Ge₂Sb₂Te₅ films

Changes in the electrical resistance of nitrogen incorporated Ge2 Sb2 Te5 (NGST) films were investigated as a function of nitrogen content by four-point probe and ac two-point probe methods. Some nitrogen is initially located inside the cubic structure, resulting in a significant increase in crystalline temperature and electrical resistance. As the amount of incorporated nitrogen increases, excess nitrogen accumulates in the grain boundaries, which does not contribute substantially to the increase in electrical resistance and the crystallization temperature. The supersaturated nitrogen distorts the Ge2 Sb2 Te5 structure, resulting in a NGST film with a structure that is different from the metastable fcc structure. X-ray absorption spectroscopy revealed that Ge-N and N2 molecular states were present in the film and gradually increased in proportion to the amount of incorporated nitrogen. Moreover, the nitrogen states were very stably maintained even during the phase transition process.