Detection of N-Te bonds in the as-deposited amorphous nitrogen-doped GeTe-based phase change alloys using N K-edge XANES spectroscopy and their impact on crystallization

Using N K-edge XANES studies, we demonstrate a noticeable difference in local structure around the nitrogen atoms in as-deposited amorphous and annealed N-doped GeTe-based phase change alloys. The pronounced changes appear as a ≈ 2 eV shift in the absorption edge to higher photon energies and the overall shape of the XANES spectrum. Comparison of the experimental XANES spectrum of the as-deposited amorphous phase with ab-initio XANES simulations discloses that the as-deposited phase mainly consists of the NGe₃and the NTe₃pyramidal units in approximately equal concentration. When annealed, NTe₃units gradually rebond to the NGe₃units and at the same time N atoms diffuse through the amorphous phase to form the Ge_xN_yaggregates. Upon long-standing annealing at 400^∘C a compact interlayer of Ge₃N₄is formed in the crystalline phase.