Effect of annealing on carrier concentration in Ge2Sb2Te5 films

Abstract

Carrier concentration of phase change materials is a critical parameter that determines electrical resistivity in amorphous and crystalline states. To obtain insights into carrier concentration of amorphous and face centered cubic (fcc) crystalline Ge2Sb2Te5, the Seebeck coefficients of as-deposited and thermal annealed Ge2Sb2Te5 films were evaluated from thermopower measurements. All the samples show p-type conduction. The Seebeck coefficients of amorphous and fcc crystalline phase were +0.89 and +0.028 mV/K, which correspond to carrier concentrations of ∼1016 and ∼1020 cm−3, respectively. Carrier mobility was also estimated to be in the range 0.02–0.6 cm2/Vs in both amorphous and fcc crystalline phases. High contrast in electrical resistivity between amorphous and fcc crystalline Ge2Sb2Te5 is originated from the difference of carrier concentration.