Electrical properties of metallophthalocyanine thin films

Sandwich structures devices of type M-t/MePc/M-2 have been fabricated by successive vacuum deposition of M-1 (Ohmic hole injections contact: Au), MePc (ZnPc, NiPc) and M-2 (electrode with low work function: Al) thin films were thermally evaporate on glass substrates maintained at room temperatures under high vacuum (10(-6)torr). The DC electrical parameters and conduction processes in MePc (Phi(ZnPc)=4.7 ev) films were investigated by studying the J (V) characteristics for two contacts such Au (Phi(Au)=5.1 ev) and Al (Phi(Al)=4.28 ev). The charge transport phenomenon in the MePc films seems to depend highly on the electrode material and the temperature. The transport parameters, derived at room temperature are consistent with the values reported for some other authors on MePc's. The results indicate that the electrical properties of ZnPc films are affected by oxygen molecules where play the role of acceptor dopant. The addition of O-2 increases the conductivity of MePc thin films by several orders of magnitude. The measurement of the current according to the tension reveals the transition between Ohmic conduction for weak tensions applied (I-Omega alpha V) and space charge limited current (I-SCLC alpha V-n) for high tensions applied. Under forward bias and in the lower tension range structure exhibit an Ohmic conduction identified from current density-tension characteristics at room temperature. At high tension range, a transition from Ohmic comportment to space charge limited conduction (SCLC) has been observed. Also, a transition to exponential traps distribution mode is observed. The transport properties have been obtained from an analysis of the samples in the SCLC regime. The interaction of the charge injected with the localized states determines the behaviour of J (V).