On the band gaps and electronic structure of thin single crystalline praseodymium oxide layers on Si(111)

Abstract

The influence of stoichiometry and crystal structure on the electronic properties of single crystalline cubic PrO2(111), cubic Pr2O3(111), and hexagonal Pr2O3(0001) thin film heterostructures on Si(111) was investigated by synchrotron radiation based photoemission electron spectroscopy (PES) and x-ray absorption spectroscopy (XAS). A detailed analysis of the complex satellite structures of PES Pr 3d lines of the various Pr oxide phases is given. PES was in addition applied to study the O 2p derived valence band structure and the positions of the occupied Pr 4f state density. It is found by a combined PES-XAS study that especially the band gap values strongly depend on the stoichiometry and crystal structure of the single crystalline Pr oxide layer. Furthermore, the close structure relationship between cubic Pr2O3(111) and PrO2(111) films is probably the reason for the detection of nonstoichiometric behavior, an effect which is far less pronounced in case of hexagonal Pr2O3(0001) layers. A possible origin of this effect is given by a surface modified valence change and therefore of importance to understand in future the epitaxial overgrowth of these oxide buffer heterostructures by alternative semiconductors such as germanium.