Accurate model including Coulomb-enhanced and Urbach-broadened absorption spectrum of direct-gap semiconductors

Abstract

An accurate absorption model including Coulomb interaction and Urbach-broadened band edge has been demonstrated for direct bandgap semiconductors. We propose a steep-edged compound Lorentzian line-shape function for modeling the Urbach tail and the line broadening of exciton absorptions. The results of applying this fitting procedure to room-temperature and low-temperature absorption spectra of GaAs, InP, and InAs are presented, and a consistent set of band parameters are extracted. The analytical absorption model is suitable for a complete closed-form Kramers-Kronig transform of the absorption spectrum to obtain the refractive-index spectrum.