Fundamental Study of a Organic Semiconductor Device for Radiation Distribution Measurement

2007 Fiscal Year Final Research Report Summary

• Project/Area Number: 18560804
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Nuclear engineering
• Research Institution: Toyama National College of Technology
• Principal Investigator: TAKADA Eiji Toyama National College of Technology, Department of Electrical Engineering, Associate Professor (00270885)
• Co-Investigator(Kenkyū-buntansha): KARABAYASHI Jun Nagoya University, Graduate School of Engineering, Associate Professor (80283414) ; KURODA Hirofumi Toyama National College of Technology, Department of Chemical and Biochemical Engineering, Associate Professor (10290735) ; OKADA Hiroyuki University of Toyama, Faculty of Engineering, Professor (80233344)
• Project Period (FY): 2006 – 2007
• Keywords: Organic Semiconductor / Radiation / Measurement / Current / X-ray

Research Abstract

Semiconductor radiation detectors are advantageous in their high transforming efficiency from energy deposited by radiation to electrical charges. However, as they are composed of inorganic materials, there has been a problem that it is difficult to fabricate them in economical ways. In this study, we tried to fabricate radiation sensors using organic materials which have been developed and applied to various areas.
We fabricated a organic photodiode (PD) device with a structure of α-NPD (500A)/td-PTC (500A)/A1 (700A) on a ITO electrode. The materials were vapor deposited on the substrate at vacuum of 4.5x10^<-6>[Torr]. The anode and cathode electrodes had a dimension of 2mm-width and, consequently, the effective area was 4mm^2. In order to estimate its response to visual light, we irradiated it with visible light of 1[kW/cm^2]. By applying inverse voltage to the device, induced current became 10^5 times larger than the dark current.
Experiments with an X-ray generator have been carried out with this type of devices. With inverse bias voltage on each device, X-ray was irradiated on it with the dose rate of about 710[mSv/h]. Dark and induced current was measured with an electrometer.
When irradiated with X-rays, the current increased with about 40[pA] to 50[pA] compared with the dark current. The induced current increased with increasing the bias voltage. This can be explained that the increased voltage resulted in larger depleted layer inside the device. Also when the acceleration voltage was increased, the induced current increased. It can be said that these results have demonstrated that the organic PD can work as radiation detector
As there is a problem that the relation between bias voltage and dark current is unstable, fabrication process and device structure should be optimized. We are going to examine the possibility of fabricating radiation imaging device with organic PDs.