Localized states evolution and nitrides separation before crystallization in nitrogen incorporated GeTe: Evidence from ellipsometric spectra

The evolutions of localized states, dielectric functions, and electronic band structure for nitrogen (N) incorporated GeTe (NGT) as functions of temperature (210-660 K) and N concentration (0%-18%) have been investigated with the aid of temperature dependent spectroscopic ellipsometry experiments. The increased Urbach absorption energy, caused by band-tail localized states, can be attributed to the increment of structure defects with N concentration, which is generated from the N atoms bonding with Ge. Besides, the details of the dynamic crystallization process and the role of nitrogen in NGT films have been elucidated by the abnormal behavior of interband transition energy and the evolutions of surface morphology, namely, the nitrides separation before crystallization and the inhibition on GT crystallization. The dynamic crystallization process and the nitrogen behavior in NGT are of great significance for further study on the reliability and endurance of the NGT-based data storage devices.