Theory of the linear and nonlinear optical properties of semiconductor microcrystallites

TLDR

The small quantum dot limit is more readily achieved with narrow‑band‑gap semiconductors. The study theoretically analyzes the optical properties of ideal semiconductor quantum dots that exhibit full quantum confinement. The authors model the linear spectrum of quantum dots smaller than the bulk exciton size as discrete lines broadened by phonons. The lowest interband transition behaves as a two‑level system, and phonon‑broadened absorption can be large enough to induce optical bistability via strong local‑field effects.

Abstract

We analyze theoretically the optical properties of ideal semiconductor crystallites so small that they show quantum confinement in all three dimensions [quantum dots (QD's)]. In the limit of a QD much smaller than the bulk exciton size, the linear spectrum will be a series of lines, and we consider the phonon broadening of these lines. The lowest interband transition will saturate like a two-level system, without exchange and Coulomb screening. Depending on the broadening, the absorption and the changes in absorption and refractive index resulting from saturation can become very large, and the local-field effects can become so strong as to give optical bistability without external feedback. The small QD limit is more readily achieved with narrow-band-gap semiconductors.