Relation between exciton splittings, magnetic circular dichroism, and magnetization in wurtzite (Ga,Fe)N

TL;DR

This study investigates the relationship between magnetization, exciton splittings, and magnetic circular dichroism in wurtzite Ga(Fe)N, revealing that accurate modeling is essential for correct interpretation of MCD data in dilute magnetic semiconductors.

Contribution

It demonstrates the limitations of MCD in estimating exciton splittings and proposes a method to accurately evaluate magnetization from MCD spectra in (Ga,Fe)N.

Findings

MCD can overestimate exciton splittings by more than a factor of 2.

Magnetization influences exciton linewidth and oscillator strength.

Proposed method allows for accurate determination of magnetization from MCD spectra.

Abstract

The question of the correlation between magnetization, band splittings, and magnetic circular dichroism (MCD) in the fundamental gap region of dilute magnetic semiconductors is examined experimentally and theoretically taking the case of wurtzite Ga(1-x)FexN as an example. Magnetization and polarization-resolved reflectivity measurements have been performed down to 2K and up to 7T for x = 0.2%. Optical transitions originating from all three free excitons A, B and C, specific to the wurtzite structure, have been observed and their evolution with the magnetic field determined. It is demonstrated that the magnitude of the exciton splittings evaluated from reflectivity-MCD data can be overestimated by more than a factor of 2, as compared to the values obtained by describing the polarization-resolved reflectivity spectra with appropriate dielectric functions. A series of model calculations shows that the quantitative inaccuracy of MCD originates from a substantial influence of the magnetization-dependent exchange interactions not only on the spin splittings of excitons but also upon their linewidth and oscillator strength. At the same time, a method is proposed that allows to evaluate the field and temperature dependencies of the magnetization from MCD spectra. The accurate values of the excitonic splittings and of the magnetization reported here substantiate the magnitudes of the apparent $sp-d$ exchange integrals in (Ga,Fe)N previously determined.