Temperature-dependent electrical transport mechanism in amorphous Ge2Sb2Te5films

Abstract

We study the electrical transport mechanism of amorphous Ge2Sb2Te5 (GST) phase-change memory material. Amorphous GST films with 10–100 nm thicknesses were fabricated in trilayer geometry by using metal top and bottom electrodes. The temperature and voltage bias dependences of the electrical conductance were measured and analyzed using different models. Thermally activated conductance was observed at high temperatures. The estimated activation energy Ea and carrier density n were 0.36–0.45 eV and ∼1018cm−3, respectively. With a decrease in temperature, variable-range-hopping (VRH) conductivity was induced in moderate temperature range (150–250 K), which was associated with the diffusive regime. At low temperatures (T<50K), electrical transport occurred predominantly by inelastic hopping through directed chains of localized states. The localized electronic states of amorphous GST were observed experimentally by our tunneling density-of-states (DOS) measurements.