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

The change in the coefficient β pf for the Poole-Frenkel effect and the change in the conductivity in anodized Ta 2 O 5 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 10 4 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 β pf changed from that of an anomalous Poole-Frenkel effect into the normal one. These chances may be caused by the change in the ratio N d (donor density)/ N t (trap density) and in the energy of the donor levels.