Anisotropy of the carrier effective masses in bulk α-PbO

Abstract

The electronic properties of an individual α-PbO layer and bulk material consisting of stacked interacting layers are studied with the first-principle calculations. It was found that while for an individual layer the top of the valence band is extremely flat, for stacked layers it becomes dispersive due to the interlayer interaction. As a result, an effective mass of holes drops from m*h = 38m0 in a single layer to m*h = 2.44m0 in bulk α-PbO. In contrast, the conduction band is almost independent of the layer interaction: for both individual layer and bulk material the bottom of the conduction band is characterized by sharp dispersion. The electron effective mass is practically unchanged and is about m*e = 0.4m0. The calculation of the electron density distribution suggests that heavy holes are a result of a strong localization of lone pair p electrons on the oxygen atom which form the top of the valence band. A similar effect of heavy holes is observed for another photoconductor like amorphous Se (Gobrecht H. and Tausend A., in Proceedings of the International Conference on the Physics of Semiconductor, Paris, 1964 (Academic Press Inc., New York) 1965, p. 1189) for which the lone pairs of the valence electrons play an important role in photo-generation.