New Optical Models for the Accurate Description of the Electrical Permittivity in Direct and Indirect Semiconductors

TL;DR

This paper introduces new optical models based on the Tauc-Lorentz and band-fluctuations approaches to accurately describe the electrical permittivity in various semiconductors, covering absorption and high-energy regions.

Contribution

The paper presents a novel 5-parameter model that self-consistently captures Urbach tails, Tauc regions, and Lorentz oscillator features in semiconductors' permittivity spectra.

Findings

Accurately fits optical data of multiple semiconductor types.

Effectively models Urbach tail and bandgap features.

Provides comparison with existing models for validation.

Abstract

We propose new models to describe the imaginary part of the electrical permittivity of dielectric and semiconductor materials in the fundamental absorption region. We work out our procedure based on the well-known structure of the Tauc-Lorentz model and the band-fluctuations approach to derive a 5-parameter formula that describes the Urbach, Tauc and high-absorption regions of direct and indirect semiconductors. Main features of the models are the self-consistent generation of the exponential Urbach tail below the bandgap and the incorporation of the Lorentz oscillator behaviour due to electronic transitions above the fundamental region. We apply and test our models on optical data of direct (MAPbI$_{3}$, GaAs and InP), indirect (GaP and c-Si), and amorphous (a-Si) semiconductors, accurately describing the spectra of the imaginary part of the electrical permittivity. Lastly, we compare our models with other similarly inspired models to assess the optical bandgap, Urbach tail and oscillator central resonance energy.