Effect of Nitrogen Implantation with Low Dose on Thermomechanical Properties and Microstructure of Ge₂Sb₂Te₅ Films

Abstract

Ge 2 Sb 2 Te 5 (GST) films with a thickness of 300 nm, in which the nitrogen (N) implant dose was 0, 10 13 , or 10 15 ions/cm 2 , were prepared by RF magnetron sputtering on Si and glass substrates. The thermomechanical properties of the GST films, viz., the biaxial modulus and coefficient of thermal expansion (CTE), were determined using the substrate curvature method for the two different substrates. The biaxial modulus of the GST films decreased with increasing N dose, whereas the CTE varied only slightly. The dependence of the microstructure on the N implantation dose was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy (FE-SEM). The lattice parameter of the crystalline structure increased with increasing N dose, which indicated the distortion of the lattice by the implanted N atoms. Because the crystallite size increased with increasing N dose, grain growth refinement caused by the formation of nitrides did not occur. Also, the presence of nitrides in the N-implanted GST film was not observed in the binding energy spectra of 1s for the N element.

Reduction of Rocksalt Phase in Ag -Doped Ge2Sb2Te5 : A Potential Material for Reversible Near-Infrared Window

“…This suggested that the nitrogen atoms occupy either vacancies or tetrahedral interstitial sites, causing a shift in the characteristic peaks and increase of the lattice parameter. Direct phase transition to the hcp phase was also verified with nitrogen implantation [24,25]. A nitrogen implantation dose higher than 4.51 × 10 16 cm −2 resulted in direct transition from the amorphous phase to the hcp phase, with suppression of the fcc phase [24].…”

“…Many researchers are also interested in suppressing the rocksalt phase or the hexagonal-close-packed (hcp) phase of GST by doping it with an appropriate element to make it a potential candidate in various applications. The suppression of these phases of GST was reported by various researchers using different doping materials [21][22][23][24][25][26][27]. Seo et al [21] found that addition of 10% Al to Ge 2 Sb 2 Te 5 served as a center for the suppression of fcc-to-hcp transition, which led to a single-step crystallization process (i.e., amorphous to fcc phase).…”

“…Seo et al [21] found that addition of 10% Al to Ge 2 Sb 2 Te 5 served as a center for the suppression of fcc-to-hcp transition, which led to a single-step crystallization process (i.e., amorphous to fcc phase). Similarly, addition of nitrogen [22][23][24][25], oxygen [26], or selenium [27] to GST played a role in suppressing the fcc phase and led to direct transition from the amorphous phase to the hcp phase. Jeong et al [22] studied the effect of nitrogen addition from 2 to 31 at.% and suggested that addition of 31 at.% nitrogen in GST thin films leads to the hcp phase.…”