Xin Tong - Quantum Dot Photodetectors

Lecture Notes in Nanoscale Science and Technology (LNNST) aims to report latest developments in nanoscale science and technology research and teaching quickly, informally and at a high level. Through publication, LNNST commits to serve the open communication of scientific and technological advances in the creation and use of objects at the nanometer scale, crossing the boundaries of physics, materials science, biology, chemistry, and engineering. Certainly, while historically the mysteries in each of the sciences have been very different, they have all required a relentless step-by-step pursuit to uncover the answer to a challenging scientific question, but recently many of the answers have brought questions that lie at the boundaries between the life sciences and the physical sciences and between what is fundamental and what is application. This is no accident since recent research in the physical and life sciences have each independently cut a path to the edge of their disciplines. As both paths intersect one may ask if transport of material in a cell is biology or is it physics? This intersection of curiosity makes us realize that nanoscience and technology crosses many if not all disciplines. It is this market that the proposed series of lecture notes targets.

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Photodetectors are optoelectronic devices that enable conversion of photons into charge carriers to generate electric signals; they have seen widespread use in modern militaries as well as civilian life, which includes night-vision, imaging technique, optical communication, surveillance system and environment monitoring. Photodetectors can be generally classified as X-ray, ultraviolet (UV), visible and infrared (IR) photodetectors based on the detection wavelength, which can be achieved by employing various photo-active semiconductor materials with different band gaps during device fabrication. Nowadays, the majority of the commercial photodetectors used in electronic devices consist of inorganic semiconductors such as silicon and IIIV compounds, showing relatively high cost, complicated fabrication processes and limited mechanical flexibility. Thus, it is of significant importance to develop large-area and flexible photodetectors with a reduction in the size, weight, power and cost (SWaP-C) for applications in a new generation of optoelectronics.

Quantum dots (QDs) are small-sized semiconductor nanoparticles synthesized by top-down methods such as epitaxial self-assembly growth and chemical colloidal synthesis, showing outstanding light harvesting and emitting properties, which are promising for the fabrication of various optoelectronic devices including photodetectors. Generally, QDs possess a physical size smaller than the Bohr radius of bulk materials, resulting in unique quantum confinement effect that enables the size-dependent band gaps for broad absorption and tunable optical detection. Over the past few decades, several types of QDs including self-assembled QDs, colloidal II-VI/IV-VI/I-III-VI QDs, perovskite QDs, carbon QDs and their hybrids of zero dimensional QDs/two-dimensional (2D) materials with improved optical and electrical properties were developed and employed to achieve high-performance QD photodetectors, representing an exciting field that has a strong impact in terms of both physics and devices, thus paving the way for the developments of next-generation photodetectors.

This book consists of the latest advances in QD-based photodetectors including the rational synthesis of QDs, the device structure design and fabrication as well as novel optical engineering/manipulating technologies of QD photodetectors. Specifically, QD photodetectors for infrared photodetection is the major topic of the chapter , QDs preparation, fundamental properties, device types of various QD infrared photodetectors based on self-assembled QDs (e.g., InAs, GaAs) and colloidal QDs (e.g., HgTe, PbS) are reviewed. The imaging arrays techniques of QD infrared photodetectors and the comparison of colloidal QD photodetectors and HgCdTe photodiodes are discussed as well.

Chapters aims to introduce and compare the lead-based and lead-free perovskite QDs by summarizing their synthesis processes, bandgap engineering, modification methods, optoelectronic properties and photoconductor devices applications. The major challenges that need to be addressed in the future and the outlooks of perovskite QDs/NCs photodetectors were presented.

In the chapter , the application of carbon and graphene QDs (C/GQDs) in high-performance photodetectors are presented. The controlled synthesis of QDs, device structures, working mechanisms and the use of C/GQDs in hybrid structures with 2D materials for improved photodetectors performance are reviewed.