Investigation of Phase Segregation Dynamics in Ge-rich GST Thin Films by In-situ X-ray Fluorescence Mapping

Abstract

Ge-rich Ge-Sb-Te alloy is a good candidate for future automotive applications due to its high crystallisation temperature, which allows good data retention at elevated temperatures. Crystallization in this material is governed by elemental segregation which is key to thermal stability and device performance. In this work elemental (Ge, Sb, Te) segregation is studied in situ during thermal annealing of Ge-rich Ge-Sb-Te thin films using X-ray fluorescence microscopy at ID16B beamline of ESRF with a beam size of 50 nm. Spatially resolved maps of Ge, Te and Sb fluorescence yield are monitored and statistically analysed as function of temperature/time. In all investigated samples Sb appears to segregate much less than Te and Ge, indicating a lower mobility of this element. In situ fluorescence mapping of samples doped with different amounts of carbon by ion implantation shows that carbon delays Ge and Te segregation to higher temperatures. Comparison with crystallization kinetics monitored by X-ray diffraction shows a good correlation between the occurrence of spatially resolved chemical inhomogeneities and the appearance of crystallised phases.