Mineral semiconductors from group III-V have been vastly used for fabrication of optoelectronic devices for long times. However, the use of organic materials as another category of semiconductors has been considered during the last decades. Comparing both category of semiconductors shows that even though the fabrication process of organic devices has lower costs, devices based on mineral (inorganic) semiconductors usually benefit from higher speeds. The use of both types of semiconductors alongside of each other provides the possibility of utilization of both types’ merits; so that this idea has been considered for developing of photodetectors. Recent vast use of organic semiconductors in optoelectronics devices has intensified the need for precise analysis and understanding the physical governing phenomena in organic devises. In this research, the operation principle of silicon/organic hybrid photodetectors with type II of heterojunction has been analyzed in the infrared spectrum. In hybrid silicon/organic photodetectors, the effective light absorption occurs at the heterojunction interface even though the semiconductors which are used in the detector are traarent in that spectrum. The absorption occurs due to the deference of energy levels at the interface silicon/organic heterojunction. Thus, in this thesis the device has been fully analyzed and modeled based on the involving physical phenomena. The model has been implemented with the aid of the COMSOL software. Furthermore, a prototype of the device was fabricated by exploiting available equipment in the lab. The simulation results have also been verified by comparing with the experimental reported data and with the measurements obtained from the fabricated prototype. This simulation model was used for device optimization regarding the dark current, responsivity and bandwidth. The results of this research show that the speed and the responsivity are increased by reducing the organic layer thickness. However, to avoid the short circuit within organic layer and depends on the fabrication process there is a limit in the thickness reduction. Another key parameter is the value of the LUMO energy level in the organic material that must be appropriately engineered. In fact, increasing the LUMO level in the organic semiconductor gives rise an absorption improvement in the infrared spectrum while degrades the dark current. According to the simulation results and the fabricated prototype device, the LUMO energy level of 4.4 eV for the organic semiconductor alongside a p-type silicon can be an appropriate choice for reducing the thermionic dark current and improving the infrared absorption. Keywords , organic semiconductors, silicon/organic hybrid photodetectors, type II of heterojunction.
