Abstract
Phase-change chalcogenide semiconductor films are widely used in non-volatile phase-change memory devices, and their properties can be controlled through nitrogen doping. Films with high nitrogen doping levels are of particular interest. In this work, the composition, structure, laser-induced structural transformations, and current–voltage characteristics of highly nitrogen-doped phase-change Ge₂Sb₂Te₅ (GST) thin films (NGST) were investigated. Amorphous NGST films with a nitrogen concentration of 22 at.% were deposited by ion-plasma reactive RF magnetron sputtering in an Ar+N₂ atmosphere. The highly nitrogen-doped NGST films in the temperature range from 25 to 330°C exhibit a single phase transition at 169°C, and, after crystallization, form a stable heterophase structure with a high degree of crystallinity (76%), comprising Sb₂Te₃, β-Ge₃N₄, and fcc-GST phases. The formation of the nitride phase results in a nanostructured composite (with crystallite sizes ranging from 11 to 21 nm, depending on the annealing temperature) that exhibits enhanced thermal stability of the matrix. Therefore, when GST films are doped with nitrogen to a concentration of 22 at.%, the crystallization temperature increases from 153 to 169°C, the threshold energy for laser-induced crystallization increases from 6.6 to 10.2 mJ, and the threshold voltage for the electrically induced transition from the high-resistance amorphous state to the low-resistance crystalline state increases from 1.20 to 3.20 V. The resulting NGST heterophase films constitute a structurally and chemically coherent system in which, upon laser irradiation, a sequence of stable states with varying degrees of crystallinity is realized.