Absorption spectrum of doped highly mismatched alloys

TL;DR

This paper predicts the unique absorption spectrum of doped highly mismatched alloys, revealing their unusual electronic structure and transition behaviors, especially near the absorption edge, through analytical models.

Contribution

It provides the first detailed prediction of the absorption spectrum in HMAs considering conduction band anticrossing effects and transition suppression.

Findings

Peak near the absorption edge due to transition suppression

Distinct spectral features from standard semiconductors

Dominance of indirect transitions away from the absorption edge

Abstract

Highly mismatched alloys (HMA's) are a class of semiconductor alloys with large electronegativity differences between the alloying elements. We predict the absorption spectrum due to transitions between the split bands of a doped highly mismatched alloy with a conduction band anticrossing. We analyze the joint densities of states for both direct and indirect transitions between the split bands. The resulting spectrum has features that reveal the unusual state distribution that is characteristic of HMAs, hence providing valuable insight into their electronic structure. In particular, we predict a peak near the absorption edge, which arises due to the suppression of direct transitions at large momenta. We present analytic forms for the near-absorption-edge and large-energy spectra, showing that they are qualitatively different from those in standard parabolic semiconductors. In particular, as a result of suppressed direct transitions, indirect transitions dominate the spectrum away from the edge of absorption.