Influence of Cu-Zn disorder in Cu_2ZnSnSe_4 absorbers on optical transitions: A spectroscopic ellipsometry study

摘要

Spectroscopic ellipsometry is applied to investigate the effect of Cu/Zn disorder in a Cu2ZnSnSe4 crystal on the optical transitions. We observe that the degree of order has an impact not only on the first optical transition E-0 at the gamma point, which is the commonly discussed direct band gap in kesterites. It also varies the further optical transition E-1 away from the gamma point. While E-0 shows an increasing trend with higher degree of order, the transition E-1 shows an opposite behavior, indicating a fundamental impact of disorder on the shape of the electronic bands of kesterite material.