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In this talk we present some recent theoretical results on the study of tunneling and current-voltage (I-V) characteristics of metallic cat whisker point-contact diodes. These point-contact devices, which currently have the fastest response times (∼< 2 orders of magnitude) of all infrared and optical detectors (e.g., Josephson tunneling devices, Schottky barrier diodes, etc.) [1], have applications to precision frequency measurements [1-3] as well as in quantum electronics and solid-state physics [4], including infrared studies of superconductivity [5]. The structure is made of an ultra-fine metal tip, comparable to those used in field emission (i.e., ∼10− 2 - 1 μm radius) in contact with a flat metal anode. A fundamental application of these devices has been the most precise and accurate determination of the velocity of light [1-3,6,7].

In this paper we wish to report some recent theoretical results on the effect of the image and multiple image interactions on the tunneling and rectification characteristics of metallic cat-whisker diodes used in precision determinations of infrared laser frequencies [1-3]. The structure is an ultra fine metal tip (< 1 μm radius) in contact with a flat metal anode separated by a distance of the order of 10-40 A. It has been suggested that the diode configuration can be considered a MOM planar tunneling junction described by Simmons theory [1,4]. The authors have questioned the applicability of the Simmons MOM model, based upon planar geometry, to the cat-whisker diode configuration and refined the model, using somewhat different solid state mechanisms [5-7]. This new model includes a thermally enhanced field induced tunneling process to explain the nonlinearity of the devices and a new rectification mechanism, independent of material asymmetry, which takes into account explictly the geometrical shape of the electrodes [8-10]. That is, the actual curvature of the tip gives rise to a nonuniform electric field across the metal-vacuum-metal (MVM) or metal-oxide-metal junction. As a consequence of the nonuniform field distribution, there is a different tunneling barrier for forward and reverse bias which leads to rectification [9].