Preface

French scientist P. Aigrain introduced the term "photonics" in 1967. This term encompasses light generation (lasers or light-emitting diodes [LEDs]), organic LEDs (OLEDs), light transmission (through free space or guided structures), processing (modulation, switching, etc.), and detection of both light and images. This book examines LEDs/OLEDs and photodetectors (PDs).

Section 1, "Light-Emitting Diodes and Organic Light-Emitting Diodes," includes three chapters discussing recent reviews and important modernizations in evaluating lighting systems. Chapter 1 discusses the operation and mechanisms of OLEDs. Chapter 2 presents an overview of LEDs, including information on their economic benefits and ratings of outdoor high-intensity discharge (HID) lights, smart control of road lighting, and intelligent design of indoor LED lights in industrial buildings. Chapter 3 evaluates LED driver circuits based on different supply sources and power requests.

Section 2, "Photodetectors," includes five chapters presenting recent developments in the photo-detection field. Photodetectors (PDs) are devices able to convert light into a measurable electrical signal, mainly taking advantage of two approaches: 1) the use of the incident photon flux to generate excitons within specific materials and 2) the use of materials characterised by strongly temperature-dependent properties. Chapter 4 reports on silicon (Si) PDs, which have been widely developed in the visible spectrum for the realisation of high-performance complementary metaloxide semiconductor (CMOS) sensors. Nowadays, Si is becoming an ideal platform for detecting the short-wavelength infrared (SWIR) spectral band thanks to the integration of Si with 2D materials. Chapter 5 discusses 2D materials like transition metal dichalcogenides (TMDs), black phosphorous, silicene, and graphene. It also presents the advances of PDs based on 2D materials and the main heterostructures. Chapter 6 introduces a new type of group-10 noble TMDs (NTMDs) that demonstrate the capability to realize PDs characterized by ultra-broad detection waveband (200 nm to 10.6 μm), fast response time, high responsivity and detectivity, and polarization sensitivity. Chapter 7 describes the evolution in the field of III-nitride semiconductors and their employment to the realization of structures for next-generation PDs. Finally, Chapter 8 presents a comparative study of a long-wavelength vertical cavity surface-emitting laser (LW-VCSEL) adapted to work as a PD and the standard PIN PDs.

This book provides readers with a detailed overview of the most recent advances in the fascinating world of both LEDs and PDs as well as explores some possible future directions in the field. This book is for students and scientists working in the field of photonics and advanced technologies.

We thank all the contributors to this book as well as Anja Filipovic and Mia Vulovic at IntechOpen for their valuable assistance during the preparation and publication of this book.

Dr. Maurizio Casalino wishes to thank his wonderful family for all the joy they bring to his life and for their constant support, in particular his wife Carla and his children Matteo and Irene.

> **Dr. Maurizio Casalino** Institute of Applied Science and Intelligent Systems "Eduardo Caianiello", National Research Council, Italy
