Fundamental Study of a Organic Semiconductor Device for Radiation Distribution Measurement

半导体辐射检测器的优点在于其从由辐射沉积的能量到电荷的高转换效率。然而，由于它们由无机材料组成，因此存在难以以经济的方式制造它们的问题。本研究尝试利用已开发并应用于多个领域的有机材料制作辐射传感器，在ITO电极上制作了α-NPD（500 A）/td-PTC（500 A）/A1（700 A）结构的有机光电二极管（PD）器件。在4.5 X 104 [Torr]的真空下将材料气相沉积在基板上<-6>。阳极和阴极电极的尺寸为2 mm宽，因此有效面积为4 mm^2。为了估计它对可见光的反应，我们用1[kW/cm^2]的可见光照射它。通过对器件施加反向电压，感应电流变为暗电流的10^5倍，用这种器件进行了X射线发生器实验。在每个器件上施加反向偏压，以约710[mSv/h]的剂量率对其照射X射线。用静电计测量暗电流和感应电流，当用X射线照射时，电流比暗电流增加约40[pA]至50[pA]。感应电流随偏压的增加而增加。这可以解释为增加的电压导致器件内部更大的耗尽层。此外，当加速电压增加时，感应电流增加。可以说，这些结果表明，有机PD可以作为辐射探测器工作。由于存在偏置电压和暗电流之间的关系不稳定的问题，需要优化制造工艺和器件结构。我们将研究用有机PD制造辐射成像器件的可能性。

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 detectorAs 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.