Quantum Dots

Authored by: Stanko Tomić , Nenad Vukmirović

Handbook of Optoelectronic Device Modeling and Simulation

Print publication date:  October  2017
Online publication date:  October  2017

Print ISBN: 9781498749466
eBook ISBN: 9781315152301
Adobe ISBN:

10.1201/9781315152301-13

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Abstract

Semiconductor nanocrystals or quantum dots (QDs) are the subject of intensive research due to a number of novel properties, which make them attractive for both fundamental studies and technological applications [16]. QDs are of particular interest for solar cell applications due to their ability to increase efficiency via the generation of multiexcitons from a single photon [79]. QDs can be synthesized with a high degree of control using colloidal chemistry [10, 11]. Much research effort has been directed toward studying QDs grown from more than one semiconductor, e.g., core/shell heterostructures [1214]. Such core/shell nanostructures provide means to control the optical properties by tuning the electron–hole wave function overlap, which is affected by the alignment of the conduction band (CB) and valence band (VB) edges, as well as the QD shape and size [1517]. In addition, such core/shell structures can provide for type-II alignments with staggered CB and VB edges so the lowest energy states for electrons and holes lie in different spatial regions, leading to charge separation between the carriers. Such staggered band alignments have several useful physical consequences, including longer radiative recombination times for more efficient charge extraction in photovoltaic applications [18, 19], optical gaps that can be made smaller than the bulk values of constituent materials [12, 20, 21] and control of the electron–hole wave function overlap that determines the exchange interaction energy [22]. Charge separation in type-II QDs can also be used to increase the repulsion between like-sign charges in biexciton states [23, 24], leading to the possibility of lasing in the single exciton regime [6, 25, 26].

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