Study on the radiation detector using new semiconductor materials.

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The silicon semiconductor detector plays an indispensable role as the vertex detector at current and possibly also in future high energy physics experiments. However, the physical dimensions of such detectors are limited to small sizes because the silicon crystal is very expensive. In order to make cheaper and larger detectors, the possibility of utilizing the organic semiconductor as a radiation detector is being investigated.A study of new radiation detectors using organic semiconductors as sensors has been made. An amplifier is connected to an organic semiconductor sensor. When laser light is injected to the sensor, an output signal was measured with ADC and Flash ADC by using a NIM and CAMAC online data acquisition system. By analysis of the experimental data, we could obtain bias voltage dependence of pulse height, S/N ratio, and response time (rise time of the signal). Pulse height and S/N ratio showed plateau above 300V for the polythiophene sensor having an electrode gap of 5 mm.For the polyaniline sensor, for which the bias voltage was fed across the film thickness (several tens of microns), no plateau appeared up to 300V. Signal rise times are about 10 us and less than 100 ns for the polythiophene sensor and the polyaniline sensor, respectively.Judging from the result of our study, we think that the best organic semiconductors suitable to be used as radiation sensors are polythiophene and polyaniline.