Isfahan University of Technology

Department of Electrical and Computer Engineering

Issue date: January 10, 2015

Degree: MSc

Language: Farsi

Contributor: Fatemeh Jahangard

Supervisor: Dr. Asghar Gholami

Counselor: Dr. Masood Omoomi

Keywords: Organic material, Photodetector, Exciton, Carrier drift and diffusion, Sensivity, Bandwidth.

Abstract

Organic photodetectors have unique properties such as mechanical flexibility, light weight, easy and low cost fabrication processes that have no need for lithography. These devices are widely used in sensors, scanners and other fields such as industry, medicine, military and astronomy which indicate the importance of these components.

The development of optimized OPDs has attracted great attention recently. To improve the performance of such devices, the knowledge of their physical behavior and an accurate model are necessary. Thus, this research is devoted to exact modeling of organic photodetectors. To verify and evaluate its ability for providing reliable results and consistent with reality, the results of simulations have been compared with the experimental data extracted from one of the references. After verifying the model accuracy, we have used the results of prepared simulator to improve the device performance. Optimization of the desired structure has been achieved from two perspectives by changing materials and layers thickness. These factors increase the amount of absorbed optical power and consequently lead to increase of the output photocurrent. Analyzing the results show that there are a trade-off between the optimized bandwidth and the high sensitivity. In most cases, increasing the thickness of active layers leads to decrease the system bandwidth, but its effect on the sensitivity isn’t easily predictable. This is due to presence of thin layers i.e. comparable with illuminated optical wavelength, which have direct influence on optical electric field within the OPD structure. Adjustment the peak of optical intensity in absorbent areas by selecting the layers thicknesses, gives rise to increase the device sensitivity while having a few influence on reducing the bandwidth.

Finally, the optimized structure is proposed by selecting materials and appropriate thickness of layers while considering the criteria of bandwidth and sensitivity. This optimization increase device sensitivity by 42.33 % however its bandwidth is decreased by 46.68 %.