INVESTIGATION OF ENERGY BAND DIAGRAM OF ORGANIC ULTRA-THIN FILM BY SIMULTANEOUS MEASUREMENT OF TUNNELING AND DISPLACEMENT CURRENTS

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The purpose of this investigation was to clarify the energy band diagram of organic ultra-thin film by simultaneous measurement of tunneling and displacement currents. This investigation has been carried out on the basis of the idea of simultaneous measuring method of tunneling and displacement currents proposed by the investigator. As a first step, the investigator has succeeded to measure the tunneling and displacement currents on semiconductor simultaneously by vibrating the scanning probe to the semiconductor surface The theoretical displacement current versus voltage curve was analyzed and was fitted to the experimental results., The theoretical displacement current curves are in good agreement with the measurement. Then, the investigator has developed the determination methods of local carrier concentration and trapped surface charge density of semiconductor. To clarify the relationship between the conduction current and space charge of organic ultra-thin film, polyimide film was … More spin-coated onto the thermally oxidized silicon substrate. The tunneling and displacement current of polyimide (3 nm in thickness) / SiO2 (1 nm in thickness) / silicon structure have been measured. The space charge density in polyimide film has been determined by displacement current curves. The density of state dependence was estimated by differential tunneling current spectroscopy and was found to be originated to the silicon. These results indicate that the polyimide film act as a insulator with space charges and that the density of states and space charges of conductive ultra-thin organic films can be determined by this method. The results were summarized as follows: (1) Measurement of semiconductor local carrier concentration from displacement current-voltage curves with a scanning vibrating probe. (2) Wave form separation of displacement and tunneling currents using a scanning vibrating probe. (3) Determination of surface space charge density on semiconductor from displacement current-voltage curve using a scanning vibrating probe. (4) Measurements of scanning tunneling spectroscopy of polyimide / SiO2 / silicon structure by using the scanning vibrating probe. Less