Photoemission signature of excitons

TL;DR

This paper develops a theoretical framework to analyze the photoemission spectrum of excitons, revealing how spectral features relate to exciton properties and semiconductor characteristics, aiding experimental identification.

Contribution

It introduces a new expression for the angle-resolved photoemission spectrum of excitons, linking spectral features to exciton and band structure properties.

Findings

Spectrum reveals direct/indirect band gap nature

Spectrum is located below conduction band minimum by binding energy

Energy integrated spectrum estimates exciton Bohr radius

Abstract

Excitons - the particle-hole bound states - composed of localized electron-hole states in semiconducting systems are crucial to explaining the optical spectrum. Spectroscopic measurements can contain signatures of these two particle bound states and can be particularly useful in determining the characteristics of these excitons. We formulate an expression for evaluating the angle-resolved photoemission spectrum arising from the ionization of excitons given their steady-state distribution in a semiconductor. We show that the spectrum contains information about the direct/indirect band gap nature of the semiconductor and is located below the conduction band minimum displaced by the binding energy. The dispersive features of the spectrum contains remnants of the valence band while additional interesting features arise from different exciton distributions. Our results indicate that for most exciton probability distributions, the energy integrated photoemission spectrum provides an estimate of the exciton Bohr radius.