Effect of N-implantation on the structural and electrical characteristics of Ge2Sb2Te5 phase change film

In this paper, the effect of nitrogen implantation on the structure and sheet resistance of Ge2Sb2Te5 film was studied in details. It is indicated that the phase transition of Ge2Sb2Te5 film from face-centered-cubic (FCC) to hexagonal (HEX) structure was suppressed by nitrogen implantation. From the results of X-ray diffraction, Raman spectra, and X-ray photoelectron spectroscopy measurements, more Te atom bonds to Sb-Sb bond and N atom bonds to Ge atom forming Ge3N4 in the nitrogen-doped Ge2Sb2Te5 film with the increase of implant dose. The sheet resistance of Ge2Sb2Te5-N film decreases with the increase of implant dose at low annealing temperature because the unit cell of crystalline Ge2Sb2Te5 film with FCC structure was distorted due to nitrogen atom occupying the tetrahedral interstitial site and the defects in film increased, which results in larger number of current carrier. On the contrary, the sheet resistance of Ge2Sb2Te5-N film increases slightly with the increase of implant dose at high annealing temperature. The two major reasons may be that the grain refinement, which results in being scattered of current carrier by grain boundary, and the suppression of phase transition from FCC to HEX structure.