II-VI Semiconductor Nanocrystals as Isolated Quantum Dots and in Complex Structures

Abstract

Semiconductor crystallites which are 10's of Angstroms show a striking evolution of electronic properties with size.1 These particles (quantum dots) are large enough to exhibit a crystalline core, but small enough that solid state electronic and vibrational band structure is not yet developed. We use a recently developed synthetic method for the fabrication of high quality nanometer size (1-10 nm) II- VI semiconductor crystallites with narrow size distributions (σ<5%), emphasizing CdSe.2 Optical characterization of their electronic structure reveals both molecular and bulk-like characteristics as well as properties which are unique to nanometer size crystallites. We observe a number of discrete electronic transitions, assign them as coming from the creation of delocalized "particle-in-a- sphere" states using the theory of Ref. 3, and study their dependence on crystallite diameter.4