Study on the crystallization by an electrical resistance measurement in Ge2 Sb2 Te5 and N-doped Ge2 Sb2 Te5 films

An electric resistance measurement was used to study the crystallization process of Ge2 Sb2 Te5 (GST) and N-doped Ge2 Sb2 Te5 (N-GST) films. The relation between conductivity and annealing time was investigated and the crystallization parameters were determined directly by resistance measurement during isothermal crystallization process in the amorphous GST and the N-GST films. The results show that the crystallization processes in both GST and N-GST films are layer by layer. Their conductivities satisfy the equation = c - (c - a) exp (-k tn), at t>τ, where τ is a temperature-dependent time in the process of crystallization. The activation energy for crystallization of amorphous GST films was 2.11±0.18 eV and the Avrami coefficient was between 2 to 4, in close agreement with previous studies using different techniques. After N doping the Avrami coefficient decreased, while the activation energy increased. The formation of a strain induced by the distortion of unit cell after N doping was used to explain the observed results.