Effect of free carriers and impurities on density of states and optical spectra of two-dimensional magneto-excitons

TL;DR

This study investigates how free carriers and impurities influence the density of states and optical spectra of two-dimensional magneto-excitons in quantum wells under high magnetic fields, combining theoretical calculations with experimental data.

Contribution

It provides a detailed analysis of the effects of free carriers and impurities on magneto-excitons, highlighting the formation of bound trion states and their spectral signatures.

Findings

DOS gaps are filled by exciton-electron interactions, creating discrete peaks.

Additional peaks in absorption spectra are linked to bound trions.

Experimental photoluminescence confirms theoretical predictions.

Abstract

Density of states (DOS) and absorption spectrum of weakly doped, narrow quantum wells in high magnetic fields are calculated by realistic exact diagonalization. The systems containing an electron--hole pair with and without an additional, second electron are compared. In DOS, the exciton--electron interaction is shown to fill the gaps between Landau levels and to yield additional discrete peaks corresponding to bound trion states. In absorption, interaction with the additional free electron causes no shift or renormalization of main, excitonic peaks. However, it results in additional, weaker peaks associated with bound trions in the lowest or higher Landau levels. The calculation is supplemented with experimental photoluminescence and photoluminescence-excitation studies of two-dimensional holes and electrons in high magnetic fields.