Abstract
AbstractColloidal quantum dots (QDs) have unique optical and electrical properties with promising applications in next‐generation semiconductor technologies, including displays, lighting, solar cells, photodetectors, and image sensors. Advanced analytical tools to probe the optical, morphological, structural, compositional, and electrical properties of QDs and their ensemble solid films are of paramount importance for the understanding of their device performance. In this review, comprehensive studies on the state‐of‐the‐art metrology approaches used in QD research are introduced, with particular focus on time‐resolved (TR) and spatially resolved (SR) spectroscopy and microscopy. Through discussing these analysis techniques in different QD system, such as various compositions, sizes, and shell structures, the critical roles of these TR‐spectroscopic and SR‐microscopic techniques are highlighted, which provide the structural, morphological, compositional, optical, and electrical information to precisely design QDs and QD solid films. The employment of TR and SR analysis in integrated QD device systems is also discussed, which can offer detailed microstructural information for achieving high performance in specific applications. In the end, the current limitations of these analytical tools are discussed, and the future development of the possibility of interdisciplinary research in both QD fundamental and applied fields is prospected.
Highlights
Quantum dots (QDs) have gained broad including displays, lighting, solar cells, photodetectors, and image sensors
As a consequence of quantum confinement in QD semiconductors, the continuous energy band alters to discrete energy, and it is more pronounced in QDs whose size is smaller than Bohr exciton radius
The lowest energy transition is 1S3/2(h)–1S(e) and the hole in the valence band (VB) and electron in the conduction band (CB) forms a pair termed as “exciton.” Exciton is characterized by their lifetime, and the path followed by the exciton during recombination crucially determines the efficiency of QD-based devices
Summary
Upon excitation with light or voltage, an electron in the VB is promoted to the energy levels of the CB leaving a hole in VB to form an exciton. If the incident energy is large, the electron and hole occupy levels higher than the lowest level, 1S and these hot excitons follow an intraband transition to release its excess energy. Electron and hole can be recombined to emit a photon known as band edge emission or make the nonradiative transition that produces heat.[32] In an ideal QD, the primary recombination will be radiative, and the quantum yield is very high, and the excitons have a lifetime of the order of nanoseconds (ns). In a typical QD, the density of trap states is high, and the nonradiative transition to these trap state is significant, and these processes occur in a timescale of few picosecond (ps) to few tens of ps. Depending on the nature of trap states, the trapped electron follows radiative or nonradiative transition.
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