Effect of Heat Treatment on the Coefficient β_pffor the Poole-Frenkel Effect and the Conductivity in Ta₂O₅Films

Abstract

The change in the coefficient βpf for the Poole-Frenkel effect and the change in the conductivity in anodized Ta2O5 films by heat treatment have been observed. Untreated films (dried at room temperature) include only neutral traps, so that the film does not exhibit the Poole-Frenkel effect and has very low conductivity. When these films are heat-treated for a few minutes in oxygen or in a vacuum, donor levels are created in the films. These films increase in conductivity by about 104 times and exhibit the Poole-Frenkel effect. When the films are heat-treated for over 10 minutes in oxygen, the conductivity decreased again. In this decreasing process, the value of βpf changed from that of an anomalous Poole-Frenkel effect into the normal one. These chances may be caused by the change in the ratio Nd (donor density)/Nt (trap density) and in the energy of the donor levels.