Effect of annealing on carrier concentration in Ge_2Sb_2Te_5 films

摘要

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 Ge_2Sb_2Te_5, the Seebeck coefficients of as-deposited and thermal annealed Ge_2Sb_2Te_5 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 ~10~(16) and ~10~(20) cm~(-3), respectively. Carrier mobility was also estimated to be in the range 0.02-0.6 cm~2/Vs in both amorphous and fcc crystalline phases. High contrast in electrical resistivity between amorphous and fcc crystalline Ge_2Sb_2Te_5 is originated from the difference of carrier concentration.