Lecture
This lecture covers the principles and applications of phototransistors, specifically focusing on BJT vertical phototransistors. It begins with an overview of the BJT structure and its operation under different conditions, including reset and illumination. The Ebers-Moll model is introduced to explain the behavior of npn phototransistors, highlighting the significance of the floating base and the sensitive base-collector junction. The lecture also discusses the characteristics of homostructure and heterostructure phototransistors, providing insights into their design and performance. Various I/V characteristics are presented, illustrating the relationship between collector light current and collector-emitter voltage. The linearity of phototransistors is analyzed, comparing their output current with that of photodiodes. Additionally, the lecture explores the use of phototransistors as optical switches and presents practical application examples, including opto-isolators and Darlington configurations. Overall, this lecture provides a comprehensive understanding of phototransistor technology and its relevance in optical detection systems.