Carrier dynamics, optical nonlinearities, and optical gain in nanocrystal quantum dots

Abstract

Nanoscale semiconductor particles in which carrier motion is restricted in all three dimensions are often referred to as semiconductor quantum dots (QDs). While the crystalline structure of the bulk solid is maintained in QDs, the three-dimensional (3D) quantum confinement imparted by the nanoscale size causes the bulk energy bands to collapse into discrete, atomic-like levels that exhibit strong size dependence.1,2 One of the approaches to fabricating sub-10 nm semiconductor nanoparticles is through chemical synthesis. Chemically synthesized QDs are also called nanocrystals or nanocrystal QDs. Synthetic methods are particularly well developed for QDs of II–VI semiconductors. The two principle chemical routes for fabrication of these QDs are high-temperature precipitation in molten glasses3,4 and colloidal synthesis using, e.g., organometallic reactions.5 Glass samples provide rigidity and environmental stability; however, they have a broad QD size distribution (typically greater than 20%) and a large number of surface defects. A much higher level of synthetic flexibility and control is provided by colloidal QDs that can be chemically manipulated in a variety of ways including size-selective precipitation5 (resulting in less than 5% size variations), surface modification by exchange of the passivation layer,6,7 formation of layered core-shell heterostructures,8,9 immobilization in sol-gel10 and polymer11 matrices, and self-assembly into 3D superlattices.12,13 KeywordsTransient AbsorptionAmplify Spontaneous EmissionHole StateAuger RecombinationOptical GainThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.