W. M. de Azevedo,

We report the development and characterization of high quality polyaniline-silicon heterojunction diodes appropriated for use as gas and/or ionizing radiation sensors. Polyaniline thin lms 40 nm thick are an active part of the junction structure, that presents excellent electrical characteristics, with rectifying ratio of 50,000 at 1.0 Volt bias. The devices are very sensitive to -radiation up to 6,000 Gy and to gas moistures such ammonia, nitric acid and trichloroethylene. The sensitivity of the diodes is observed through shifts of the current-voltage (I-V) curves which can be easily monitored to provide a calibration curve of the sensor either as a radiation dosimeter or as a gas sensor for use in applications in environments demanding gas monitoring or radiation dosimetry. In the last two decades conducting polymers emerged as a new class of material for use in advanced electronic device technologies[1, 2, 3, 4]. Their electrical conductivity can be changed from isolating to metallic by chemical or electrochemical doping. The electronic conductivity related to the redox state (doping level) of these polymers can be modulated by the interactio