Investigation of Current Carrier Drift in Organic Substances (Tetracene)

The pulses of hole conduction current induced by pulse electron bombardment in a thin sublimed film of tetracene are studied. It is shown that electrons produced by ionization cannot be extracted into the bulk of the sample by an external electric field. The hole mobility is estimated as μ ≧ 0.5 cm2/Vs. The integral of hole current per pulse is shown to rise with the applied voltage U, though special experiments demonstrate that no trapping occurs in the sample. The linear increase of the hole current integral is explained by competition between extraction of holes from the electrode‐adjacent layer and recombination of holes with electrons injected into the tetracene from the Al electrode. This conclusion is confirmed by the rectifying properties of the Al‐tetracene contact and by photovoltage. The hole current integral in the admixture containing samples is shown to be proportional to U2. This is due to a combination of two processes: the hole extraction probability increases linearly with U and also the hole displacement before trapping in the sample increases linearly with U.