Auger recombination and carrier multiplication in embedded silicon and germanium nanocrystals

TL;DR

This paper calculates Auger recombination and carrier multiplication lifetimes in silicon and germanium nanocrystals, revealing their potential to enhance photovoltaic efficiency through hot-electron-induced carrier multiplication.

Contribution

It provides exact lifetime calculations using empirical pseudopotential wave functions and introduces simple Auger constants for nanocrystals, supporting and extending recent experimental findings.

Findings

Both Si and Ge nanocrystals can improve photovoltaic efficiency via carrier multiplication.

Carrier multiplication is especially efficient for hot electrons with ~1 eV excess energy.

The study offers new predictions and supports recent experimental data.

Abstract

For Si and Ge nanocrystals (NCs) embedded in wide band-gap matrices, Auger recombination (AR) and carrier multiplication (CM) lifetimes are computed exactly in a three-dimensional real space grid using empirical pseudopotential wave functions. Our results in support of recent experimental data offer new predictions. We extract simple Auger constants valid for NCs. We show that both Si and Ge NCs can benefit from photovoltaic efficiency improvement via CM due to the fact that under an optical excitation exceeding twice the band gap energy, the electrons gain lion's share from the total excess energy and can cause a CM. We predict that CM becomes especially efficient for hot electrons with an excess energy of about 1 eV above the CM threshold.