Pergamon Solid State Communications, Vol. 97, No. 12, pp. 1059-1062, 1996 Copyright ~) 1996 Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/96 $12.00 + 0.00 0038-1098(95)00794-6 ON TUNNELING THROUGH LANGMUIR-BLODGETT-FILM BASED HETEROSTRUCTURES Yu. A. Klimenko Glushkov Institute of Cybernetics, Kiev, 252207, Ukraine Alexander I. Onipko Bogolyubov Institute for Theoretical Physics, Kiev, 252143, Ukraine (Received 2 May 1995; accepted 20 October 1995 by PH. Dederichs) The 1-d model of resonant tunneling through a weakly coupled guest molecule in quan- tum wires, which has been proposed earlier, is extended on the 3-d case, to examine the role of intermolecular electron-transfer parameters in determining the I-V characteristic of metal-LB-film-metal heterostrutures. It is shown that with a reasonable choice of pa- rameters theoretical curve perfectly fits the structure discovered recently in the through- LB-film-current dependence on the applied voltage. This suggests an explanation (al- ternative to the original version) of the step-like current structure observed in terms of linear resonant tunneling. The key experimental test of our conclusions is also indicated. Keywords: A. quantum wells, D. tunneling. THE PERSPECTIVE to obtain novel electrical and optical properties in electronic devices based on or- ganic materials has stimulated a number of attempts to employ molecular aggregates as basic functional units in tunneling junctions [1], quantum wells [2], rec- tifiers [3, 4], etc. As in the case of semiconductor het- erostructures, functioning of the molecular electronic devices is basically determined by tunneling involved processes participated by charge carriers. These pro- cesses must be strongly influenced by specific arrange- ment of molecular energy levels (or narrow conduction bands), by essentially discrete character of molecular functional unites, and by some other factors which are absent or less important in conventional electronic de- vices. Generally speaking, just distinctions in the en- ergy spectrum and in parameters of the interaction re- sponsible for the electron dynamics give rise to specific behavior of molecular electronic devices in compari- son with their semiconductor counterparts. In a very recent publication [4], the creation of a highly reproducible rectifying device based on the Langmuir-Blodgett (LB) film heterostructure has been reported. Two sets of experiments have been performed with asymmetric and symmetric LB films sandwiched between gold electrodes. In these exper- iments, the rectifying behavior is revealed only by asymmetric heterostructures. In addition, for both types of investigated LB films two effects have been observed: a well pronounced step-like structure in the I-V dependence and an abrupt increase in the current above a certain (threshold) voltage value. In this com- munication, we centre our attention on the manifes- tation of these effects in a symmetric metal-LB-film- metal heterostructure, to show that they can receive a reasonable explanation within the picture of linear resonance tunneling through a sequence of monolay- ers. In the original work [4], the step-like structure has been tentatively attributed to the Coulomb charging effect in tunneling through molecular electron levels in the LB film. However, as is shown below the form of the I-V characteristic observed in [4] may reflect, in fact, quite general properties of linear resonant tunneling through a highly ordered molecular system. Before presenting the strict quantitative description, it is instructive to consider a qualitative picture of the tunneling process through a film consisting of one type of monolayers. This picture is addressed to vertical heterostructures, where the film is placed between the bottom and top electrodes of identical metals. The properties of this structure are supposed to vary only in one (z) direction and to be uniform in transverse (_1.) directions. It is also supposed that the film-to-metal electronic coupling is weak, i.e., that the resonance integral, which determine the electron transfer from 1059