Anisotropic optical properties of highly doped rutile SnO2: Valence band contributions to the Burstein-Moss shift

Martin Feneberg,Zbigniew Galazka,Mark E White,Christian Lidig,James S Speck,Rüdiger Goldhahn,Min Y Tsai,Oliver Bierwagen

doi:10.1063/1.5054351

Abstract

The interband absorption of the transparent conducting semiconductor rutile stannic oxide (SnO2) is investigated as a function of increasing free electron concentration. The anisotropic dielectric functions of SnO2:Sb are determined by spectroscopic ellipsometry. The onsets of strong interband absorption found at different positions shift to higher photon energies with increasing free carrier concentration. For the electric field vector parallel to the optic axis, a low energy shoulder increases in prominence with increasing free electron concentration. We analyze the influence of different many-body effects and can model the behavior by taking into account bandgap renormalization and the Burstein-Moss effect. The latter consists of contributions from the conduction and the valence bands which can be distinguished because the nonparabolic conduction band dispersion of SnO2 is known already with high accuracy. The possible originsof the shoulder are discussed. The most likely mechanism is identified to be interband transitions at |k| &gt; 0 from a dipole forbidden valence band.

Highlights

There is a lack of systematic experimental studies about the optical properties of crystalline rutile SnO2 as a function of free carrier concentration in the literature
We employ state-of-the-art spectroscopic ellipsometry on a bulk SnO2 crystal and high-quality molecular beam epitaxy grown thin films doped with antimony
Generalized spectroscopic ellipsometry23 was performed on all samples in the photon energy range from 0.5 to 6.5 eV for at least three angles of incidence (θ = 60◦, 67◦, 74◦)

Summary

Introduction

There is a lack of systematic experimental studies about the optical properties of crystalline rutile SnO2 as a function of free carrier concentration in the literature. The thin-film samples have been investigated in the infrared spectral range earlier.21 Key results to be used in this study include an increase of both effective electron masses m∗⊥ and m∗ with increasing free carrier concentration, to a different extent.

Results

Conclusion