Crystallization of Amorphous N-Doped Ge-Rich GST Layers Deposited on a Polycrystalline GST Template

Herein, a detailed experimental study of the crystallization of amorphous N-doped Ge-rich GeSbTe layers (GGSTN) when in contact with a polycrystalline GeSbTe (GST template is reported on. By combining in situ annealing in the transmission electron microscope and ex situ chemical analysis, it is shown that, as observed in many materials, the layer in contact with the crystalline template crystallizes at a lower temperature than needed for bulk crystallization. At surprise, this characteristic is not due to the solid-phase epitaxy of the GGSTN on the crystalline GST template but to a decrease of the Ge content in the GGSTN layer. Indeed, during annealing, Ge diffuses from the amorphous layer into the crystalline GST layer where it gets trapped and forms grains which grow, eventually leading to the formation of a pure crystalline Ge layer. As a result of this Ge depletion, the thermal budget necessary to drive the phase separation limiting the crystallization of the remaining GGSTN alloy is smaller. In situ transmission electron microscopy and ex situ chemical analysis reveal that a nitrogen-doped Ge-rich GeSbTe (GGSTN) layer, in contact with a crystalline GeSbTe template, crystallizes at a lower temperature than needed for bulk crystallization. Contrary to expectations, the phenomenon is not attributed to solid-phase epitaxy but rather to a reduction in Ge content within the GGSTN layer.image (c) 2024 WILEY-VCH GmbH