Theory of multiexciton generation in semiconductor nanocrystals

TL;DR

This paper presents a comprehensive theoretical framework for understanding multiexciton generation in semiconductor nanocrystals, unifying existing mechanisms and introducing new limits to improve predictive accuracy.

Contribution

It develops a Green's function based theory that unifies and extends existing models, introducing weak Coulomb coupling and semi-wide band limits for better understanding.

Findings

Multiexciton generation can be modeled as an incoherent process.

Scaling of multiexciton generation depends on photon energy and nanocrystal size.

The theory is illustrated with CdSe, InAs, and silicon quantum dots.

Abstract

We develop a generalized framework based on a Green's function formalism to calculate the efficiency of multiexciton gen-eration in nanocrystal quantum dots. The direct/indirect absorption and coherent/incoherent impact ionization mechanisms, often used to describe multiexciton generation in nanocrystals, are reviewed and rederived from the unified theory as certain approximations. In addition, two new limits are described systematically - the weak Coulomb coupling limit and the semi-wide band limit. We show that the description of multiexciton generation in nanocrystals can be described as incoherent process and we discuss the scaling of multiexciton generation with respect to the photon energy and nanocrystal size. Illustrations are given for three prototype systems: CdSe, InAs and silicon quantum dots.