Estimating complete band diagrams of non-ideal heterointerfaces by combining ellipsometry and photoemission spectroscopy

In this work, we show that spectroscopic ellipsometry can he combined with photoemission spectroscopy to obtain complete interface band diagrams of non-ideal semiconductor heterointerfaces, such as interfaces between thin-film polycrystalline materials. The non-destructive ellipsometry measurement probes the near-interface bandgap of the two semiconductors (including the buried semiconductor) after the interface has formed. This is important in the non-ideal case where chemical processes during interface growth modify the electronic properties of the two separated surfaces. Knowledge of near-interface bandgaps improves accuracy in conduction band offset measurements of non-ideal interfaces, and it sheds light on their device physics. Both of those positive outcomes are demonstrated in the Cu2ZnSnS4/CdS interface used here as a case study, where the bandgap of both materials decreases by up to 200 meV from the bulk to the near-interface region. This finding reveals a preferential electron-hole recombination channel near the interface, and it yields corrected values for the interfacial conduction hand offset. Published by AIP Publishing.