Structure evolution, bandgap, and dielectric function in La-doped hafnium oxide thin layer subjected to swift Xe ion irradiation

Abstract

High-resolution transmission electron microscopy, electron diffraction, and electron energy-loss spectroscopy provide information on the structural evolution, dielectric function, and bandgap values of nanocrystalline 10 nm thick lanthanum doped hafnia (La:HfO2) layers in TiN/La:HfO2/TiN/SiO2/Si irradiated with 24, 46, 72, and 160 MeV (0.2–1.2 MeV/u) Xe ions. Swift heavy Xe ions were expected to create significant atomic rearrangements when passed through a solid losing energy mainly through electronic excitation and ionization of the target atoms. Local heating and subsequent rapid cooling in the region around the ion track can lead to re-solidification with the formation of a new stable crystalline phase, and direct crystal-to-crystal transformations are possible. The structure evolution of hafnia nanocrystals from the orthorhombic Pbcm in the pristine layer to the tetragonal P42/nmc phase in the 160 MeV Xe ion irradiated layer was observed. The mixture of tetragonal and orthorhombic phases was found in samples irradiated with ions of intermediate energies. Textured hafnia layers were formed as a result of ion irradiation. The changes in plasmon line shape and the blueshift of the plasmon energy-loss peak from 14.9 eV in the pristine layer to 15.4 eV in 46 MeV and 15.9 eV in 160 MeV Xe ion irradiated hafnia reflect structural transformations, the increase in the Hf coordination number, and crystal orientations. Valence-electron energy-loss spectroscopy measurements showed a slight increase in the bandgap value from 6.1 eV in the pristine sample to 6.2 eV and 6.3 eV in irradiated samples with 46 and 160 MeV Xe ions, respectively, and dielectric functions changed insignificantly in irradiated hafnia layers.

Structure, Oxygen Content and Electric Properties of Titanium Nitride Electrodes in TiNx/La:HfO2/TiNx Stacks Grown by PEALD on SiO2/Si

“…Since the FWHM is related to the lifetime of the plasma oscillations [ 57 ], the damping coefficient is relatively isotropic for both titanium oxynitride layers despite the small difference in oxygen content. Figure 8 also shows the low loss spectrum attributed to pure La:HfO 2 , which exhibits the following two characteristic features: (i) a bulk plasmon peak at 14.9 nm and (ii) single-particle interband transitions that contribute to the oscillator strength at about 24.9–25.0 eV, which has already been observed [ 33 , 58 ].…”

“…Accurate element quantification requires an estimate of sample thickness for X-Ray absorption correction. Assuming this thickness is constant over the whole area of interest, it was estimated by matching JEMS simulations to HRTEM images when available [ 33 ] or trial and error until the Cliff–Lorimer quantification was matching the HfO 2 or HfO 0 . 5 Zr 0 .…”

Pulse Laser Deposition of HfO2 Nanoporous-Like Structure, Physical Properties for Device Fabrication

“…This shows that the temperature of the substrate has an influence on the HfO 2 films. The transition to the crystalline phase was predicted, as previously stated [7,8,29]. The following equations were used to compute the structural characteristics of HfO 2 films [30-32]:…”

Structural and Electrical Response of Emerging Memories Exposed to Heavy Ion Radiation

“… 56 Regarding such effects occurring on a microstructural scale, especially transmission electron microscopy (TEM) has been proven to be a very powerful tool to investigate structural changes on a micrometer or nanometer scale. 54 , 57 − 59 Structural changes become especially relevant in ferroelectric and phase-change memory, as their information storage is based on the crystallinity of the active layer. Its evolution is essential for memory cell functionality.…”

“…In contrast to the radiation-induced phase transition from the monoclinic to the tetragonal structure, we recently identified the oxygen-deficient HfO x phase as a defect-stabilized variant of the monoclinic structure with a slightly rhombohedral distorted cubic symmetry (low-temperature phase of cubic HfO x , named LTP c -HfO 2– x ) in as-grown hafnium oxide films . Regarding such effects occurring on a microstructural scale, especially transmission electron microscopy (TEM) has been proven to be a very powerful tool to investigate structural changes on a micrometer or nanometer scale. ,− Structural changes become especially relevant in ferroelectric and phase-change memory, as their information storage is based on the crystallinity of the active layer. Its evolution is essential for memory cell functionality.…”