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A new method is proposed to improve the response time of organic photodetectors by using displacement current. By inserting a transparent organic dielectric layer between the organic semiconductor active layer and the electrode the displacement current will be produced and replace the conduction current for current propagation, which will overcome the disadvantage of low carrier mobility of organic semiconductors. Under the irradiation of nanosecond pulse laser the rise time and fall time of the organic photodetector based on displacement current decrease 10% and 86%, respectively comparing to the conventional organic photodetector based on conduction current, which indicates the displacement current could renew the operation principle for high-speed organic photodetectors.

Iron–phthalocyanine (FePc) organic photoconductive detector was fabricated using pulsed laser deposition (PLD) technique to work in ultraviolet (UV) and visible regions. The organic semiconductor material (iron phthalocyanine) was deposited on n-type silicon wafer (Si) substrates at different thicknesses (100, 200 and 300) nm. FePc organic photoconductive detector has been improved by two methods: the first is to manufacture the detector on PSi substrates, and the second is by coating the detector with polyamide–nylon polymer to enhance the photoconductivity of the FePc detector. The current–voltage (I–V) characteristics, responsivity, photocurrent gain, response time and the quantum efficiency of the fabricated photoconductive detector were measured. The performance of the fabricated detector was taken under dark and illumination using two types of light sources: UV LED with wavelength (365nm), power of (10W) and Tungsten lamp with wavelength range between (500–800) nm and the optical power of (250W). The photoresponse enhancement was improved by coating the FePc films with 200nm of polyamide nylon polymer. This type of coating, which can be considered as a surface treatment, highly increased the photoresponse of the fabricated FePc UV detector. The results show that the responsivity increased four orders of magnitudes more than the responsivity of the uncoated FePc film. The effects of the coated polymers on the responsivity and the response time of the detector were investigated.