Influence of the alkalis (KOH, NaOH), acids (HNO3, HCl, H3PO4, H2SO4) and solvents (C3H7NO, deionized water) on the Ge2Sb2Te5 thin films was investigated. Most possible etching mechanism of GST225 thin films by HNO3 solution was proposed.
Process of reactive ion etching of Ge2Sb2Te5 thin film was studied in the work. It was found that Ar+O2 gas mixture has a minimum etching rate (7.4 nm/min) and Ar+SF6 (37.0 nm/min) mixtures have highest etching rate. Surface roughness decreased from ~0.8 nm before etching to the value of ~0.5 nm after etching. EDXRA showed the absence of the contamination by the components of the gas mixtures after the etching.
The influence of Bi doping on the charge carrier transport mechanism in GST225 thin films was investigated. The three regions with different current-voltage dependencies were established. The energy diagrams for Bi doped GST225 thin films for different regions were analyzed. Analysis of experimental data showed that space charge limited current is the most possible explanation for the nonlinear I-V dependence in the middle electrical field strength (103 < E < 104 V/cm). Position of the trap levels (Et) controlling transport mechanism, and density of traps (Nt) were estimated with using of Rose and Lampert theories. It was established that Bi doping can significantly change I-V characteristic, resistivity, mobility gap, Urbach energy, density distribution of localized states, and activation energy of conductivity. The most pronounced modification of current-voltage characteristic and parameters of the thin films was established for GST225 + 0,5 wt. % Bi. Thus, doping of Ge2Sb2Te5 by Bi expands the range of material properties, which is important for the optimization of PCM technology.